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authorKevin Smith <git@kismith.co.uk>2012-08-17 19:46:39 (GMT)
committerKevin Smith <git@kismith.co.uk>2012-09-01 19:16:16 (GMT)
commit9bc48bf7e580a2a0962e9f62069f061315f1b3f2 (patch)
tree5b3f8769e41347e833001dca8a71ea0c22ae6050 /3rdParty/SQLite/sqlite3async.c
parenta5115d977029a8e3f4fd92c16f25208222c73b7e (diff)
downloadswift-contrib-9bc48bf7e580a2a0962e9f62069f061315f1b3f2.zip
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Add asynchronous sqlite interface
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+/*
+** 2005 December 14
+**
+** The author disclaims copyright to this source code. In place of
+** a legal notice, here is a blessing:
+**
+** May you do good and not evil.
+** May you find forgiveness for yourself and forgive others.
+** May you share freely, never taking more than you give.
+**
+*************************************************************************
+**
+** $Id: sqlite3async.c,v 1.7 2009/07/18 11:52:04 danielk1977 Exp $
+**
+** This file contains the implementation of an asynchronous IO backend
+** for SQLite.
+*/
+
+#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_ASYNCIO)
+
+#include "sqlite3async.h"
+#include "sqlite3.h"
+#include <stdarg.h>
+#include <string.h>
+#include <assert.h>
+
+/* Useful macros used in several places */
+#define MIN(x,y) ((x)<(y)?(x):(y))
+#define MAX(x,y) ((x)>(y)?(x):(y))
+
+#ifndef SQLITE_AMALGAMATION
+/* Macro to mark parameters as unused and silence compiler warnings. */
+#define UNUSED_PARAMETER(x) (void)(x)
+#endif
+
+/* Forward references */
+typedef struct AsyncWrite AsyncWrite;
+typedef struct AsyncFile AsyncFile;
+typedef struct AsyncFileData AsyncFileData;
+typedef struct AsyncFileLock AsyncFileLock;
+typedef struct AsyncLock AsyncLock;
+
+/* Enable for debugging */
+#ifndef NDEBUG
+#include <stdio.h>
+static int sqlite3async_trace = 0;
+# define ASYNC_TRACE(X) if( sqlite3async_trace ) asyncTrace X
+static void asyncTrace(const char *zFormat, ...){
+ char *z;
+ va_list ap;
+ va_start(ap, zFormat);
+ z = sqlite3_vmprintf(zFormat, ap);
+ va_end(ap);
+ fprintf(stderr, "[%d] %s", 0 /* (int)pthread_self() */, z);
+ sqlite3_free(z);
+}
+#else
+# define ASYNC_TRACE(X)
+#endif
+
+/*
+** THREAD SAFETY NOTES
+**
+** Basic rules:
+**
+** * Both read and write access to the global write-op queue must be
+** protected by the async.queueMutex. As are the async.ioError and
+** async.nFile variables.
+**
+** * The async.pLock list and all AsyncLock and AsyncFileLock
+** structures must be protected by the async.lockMutex mutex.
+**
+** * The file handles from the underlying system are not assumed to
+** be thread safe.
+**
+** * See the last two paragraphs under "The Writer Thread" for
+** an assumption to do with file-handle synchronization by the Os.
+**
+** Deadlock prevention:
+**
+** There are three mutex used by the system: the "writer" mutex,
+** the "queue" mutex and the "lock" mutex. Rules are:
+**
+** * It is illegal to block on the writer mutex when any other mutex
+** are held, and
+**
+** * It is illegal to block on the queue mutex when the lock mutex
+** is held.
+**
+** i.e. mutex's must be grabbed in the order "writer", "queue", "lock".
+**
+** File system operations (invoked by SQLite thread):
+**
+** xOpen
+** xDelete
+** xFileExists
+**
+** File handle operations (invoked by SQLite thread):
+**
+** asyncWrite, asyncClose, asyncTruncate, asyncSync
+**
+** The operations above add an entry to the global write-op list. They
+** prepare the entry, acquire the async.queueMutex momentarily while
+** list pointers are manipulated to insert the new entry, then release
+** the mutex and signal the writer thread to wake up in case it happens
+** to be asleep.
+**
+**
+** asyncRead, asyncFileSize.
+**
+** Read operations. Both of these read from both the underlying file
+** first then adjust their result based on pending writes in the
+** write-op queue. So async.queueMutex is held for the duration
+** of these operations to prevent other threads from changing the
+** queue in mid operation.
+**
+**
+** asyncLock, asyncUnlock, asyncCheckReservedLock
+**
+** These primitives implement in-process locking using a hash table
+** on the file name. Files are locked correctly for connections coming
+** from the same process. But other processes cannot see these locks
+** and will therefore not honor them.
+**
+**
+** The writer thread:
+**
+** The async.writerMutex is used to make sure only there is only
+** a single writer thread running at a time.
+**
+** Inside the writer thread is a loop that works like this:
+**
+** WHILE (write-op list is not empty)
+** Do IO operation at head of write-op list
+** Remove entry from head of write-op list
+** END WHILE
+**
+** The async.queueMutex is always held during the <write-op list is
+** not empty> test, and when the entry is removed from the head
+** of the write-op list. Sometimes it is held for the interim
+** period (while the IO is performed), and sometimes it is
+** relinquished. It is relinquished if (a) the IO op is an
+** ASYNC_CLOSE or (b) when the file handle was opened, two of
+** the underlying systems handles were opened on the same
+** file-system entry.
+**
+** If condition (b) above is true, then one file-handle
+** (AsyncFile.pBaseRead) is used exclusively by sqlite threads to read the
+** file, the other (AsyncFile.pBaseWrite) by sqlite3_async_flush()
+** threads to perform write() operations. This means that read
+** operations are not blocked by asynchronous writes (although
+** asynchronous writes may still be blocked by reads).
+**
+** This assumes that the OS keeps two handles open on the same file
+** properly in sync. That is, any read operation that starts after a
+** write operation on the same file system entry has completed returns
+** data consistent with the write. We also assume that if one thread
+** reads a file while another is writing it all bytes other than the
+** ones actually being written contain valid data.
+**
+** If the above assumptions are not true, set the preprocessor symbol
+** SQLITE_ASYNC_TWO_FILEHANDLES to 0.
+*/
+
+
+#ifndef NDEBUG
+# define TESTONLY( X ) X
+#else
+# define TESTONLY( X )
+#endif
+
+/*
+** PORTING FUNCTIONS
+**
+** There are two definitions of the following functions. One for pthreads
+** compatible systems and one for Win32. These functions isolate the OS
+** specific code required by each platform.
+**
+** The system uses three mutexes and a single condition variable. To
+** block on a mutex, async_mutex_enter() is called. The parameter passed
+** to async_mutex_enter(), which must be one of ASYNC_MUTEX_LOCK,
+** ASYNC_MUTEX_QUEUE or ASYNC_MUTEX_WRITER, identifies which of the three
+** mutexes to lock. Similarly, to unlock a mutex, async_mutex_leave() is
+** called with a parameter identifying the mutex being unlocked. Mutexes
+** are not recursive - it is an error to call async_mutex_enter() to
+** lock a mutex that is already locked, or to call async_mutex_leave()
+** to unlock a mutex that is not currently locked.
+**
+** The async_cond_wait() and async_cond_signal() functions are modelled
+** on the pthreads functions with similar names. The first parameter to
+** both functions is always ASYNC_COND_QUEUE. When async_cond_wait()
+** is called the mutex identified by the second parameter must be held.
+** The mutex is unlocked, and the calling thread simultaneously begins
+** waiting for the condition variable to be signalled by another thread.
+** After another thread signals the condition variable, the calling
+** thread stops waiting, locks mutex eMutex and returns. The
+** async_cond_signal() function is used to signal the condition variable.
+** It is assumed that the mutex used by the thread calling async_cond_wait()
+** is held by the caller of async_cond_signal() (otherwise there would be
+** a race condition).
+**
+** It is guaranteed that no other thread will call async_cond_wait() when
+** there is already a thread waiting on the condition variable.
+**
+** The async_sched_yield() function is called to suggest to the operating
+** system that it would be a good time to shift the current thread off the
+** CPU. The system will still work if this function is not implemented
+** (it is not currently implemented for win32), but it might be marginally
+** more efficient if it is.
+*/
+static void async_mutex_enter(int eMutex);
+static void async_mutex_leave(int eMutex);
+static void async_cond_wait(int eCond, int eMutex);
+static void async_cond_signal(int eCond);
+static void async_sched_yield(void);
+
+/*
+** There are also two definitions of the following. async_os_initialize()
+** is called when the asynchronous VFS is first installed, and os_shutdown()
+** is called when it is uninstalled (from within sqlite3async_shutdown()).
+**
+** For pthreads builds, both of these functions are no-ops. For win32,
+** they provide an opportunity to initialize and finalize the required
+** mutex and condition variables.
+**
+** If async_os_initialize() returns other than zero, then the initialization
+** fails and SQLITE_ERROR is returned to the user.
+*/
+static int async_os_initialize(void);
+static void async_os_shutdown(void);
+
+/* Values for use as the 'eMutex' argument of the above functions. The
+** integer values assigned to these constants are important for assert()
+** statements that verify that mutexes are locked in the correct order.
+** Specifically, it is unsafe to try to lock mutex N while holding a lock
+** on mutex M if (M<=N).
+*/
+#define ASYNC_MUTEX_LOCK 0
+#define ASYNC_MUTEX_QUEUE 1
+#define ASYNC_MUTEX_WRITER 2
+
+/* Values for use as the 'eCond' argument of the above functions. */
+#define ASYNC_COND_QUEUE 0
+
+/*************************************************************************
+** Start of OS specific code.
+*/
+#if SQLITE_OS_WIN || defined(_WIN32) || defined(WIN32) || defined(__CYGWIN__) || defined(__MINGW32__) || defined(__BORLANDC__)
+
+#include <windows.h>
+
+/* The following block contains the win32 specific code. */
+
+#define mutex_held(X) (GetCurrentThreadId()==primitives.aHolder[X])
+
+static struct AsyncPrimitives {
+ int isInit;
+ DWORD aHolder[3];
+ CRITICAL_SECTION aMutex[3];
+ HANDLE aCond[1];
+} primitives = { 0 };
+
+static int async_os_initialize(void){
+ if( !primitives.isInit ){
+ primitives.aCond[0] = CreateEvent(NULL, TRUE, FALSE, 0);
+ if( primitives.aCond[0]==NULL ){
+ return 1;
+ }
+ InitializeCriticalSection(&primitives.aMutex[0]);
+ InitializeCriticalSection(&primitives.aMutex[1]);
+ InitializeCriticalSection(&primitives.aMutex[2]);
+ primitives.isInit = 1;
+ }
+ return 0;
+}
+static void async_os_shutdown(void){
+ if( primitives.isInit ){
+ DeleteCriticalSection(&primitives.aMutex[0]);
+ DeleteCriticalSection(&primitives.aMutex[1]);
+ DeleteCriticalSection(&primitives.aMutex[2]);
+ CloseHandle(primitives.aCond[0]);
+ primitives.isInit = 0;
+ }
+}
+
+/* The following block contains the Win32 specific code. */
+static void async_mutex_enter(int eMutex){
+ assert( eMutex==0 || eMutex==1 || eMutex==2 );
+ assert( eMutex!=2 || (!mutex_held(0) && !mutex_held(1) && !mutex_held(2)) );
+ assert( eMutex!=1 || (!mutex_held(0) && !mutex_held(1)) );
+ assert( eMutex!=0 || (!mutex_held(0)) );
+ EnterCriticalSection(&primitives.aMutex[eMutex]);
+ TESTONLY( primitives.aHolder[eMutex] = GetCurrentThreadId(); )
+}
+static void async_mutex_leave(int eMutex){
+ assert( eMutex==0 || eMutex==1 || eMutex==2 );
+ assert( mutex_held(eMutex) );
+ TESTONLY( primitives.aHolder[eMutex] = 0; )
+ LeaveCriticalSection(&primitives.aMutex[eMutex]);
+}
+static void async_cond_wait(int eCond, int eMutex){
+ ResetEvent(primitives.aCond[eCond]);
+ async_mutex_leave(eMutex);
+ WaitForSingleObject(primitives.aCond[eCond], INFINITE);
+ async_mutex_enter(eMutex);
+}
+static void async_cond_signal(int eCond){
+ assert( mutex_held(ASYNC_MUTEX_QUEUE) );
+ SetEvent(primitives.aCond[eCond]);
+}
+static void async_sched_yield(void){
+ Sleep(0);
+}
+#else
+
+/* The following block contains the pthreads specific code. */
+#include <pthread.h>
+#include <sched.h>
+
+#define mutex_held(X) pthread_equal(primitives.aHolder[X], pthread_self())
+
+static int async_os_initialize(void) {return 0;}
+static void async_os_shutdown(void) {}
+
+static struct AsyncPrimitives {
+ pthread_mutex_t aMutex[3];
+ pthread_cond_t aCond[1];
+ pthread_t aHolder[3];
+} primitives = {
+ { PTHREAD_MUTEX_INITIALIZER,
+ PTHREAD_MUTEX_INITIALIZER,
+ PTHREAD_MUTEX_INITIALIZER
+ } , {
+ PTHREAD_COND_INITIALIZER
+ } , { 0, 0, 0 }
+};
+
+static void async_mutex_enter(int eMutex){
+ assert( eMutex==0 || eMutex==1 || eMutex==2 );
+ assert( eMutex!=2 || (!mutex_held(0) && !mutex_held(1) && !mutex_held(2)) );
+ assert( eMutex!=1 || (!mutex_held(0) && !mutex_held(1)) );
+ assert( eMutex!=0 || (!mutex_held(0)) );
+ pthread_mutex_lock(&primitives.aMutex[eMutex]);
+ TESTONLY( primitives.aHolder[eMutex] = pthread_self(); )
+}
+static void async_mutex_leave(int eMutex){
+ assert( eMutex==0 || eMutex==1 || eMutex==2 );
+ assert( mutex_held(eMutex) );
+ TESTONLY( primitives.aHolder[eMutex] = 0; )
+ pthread_mutex_unlock(&primitives.aMutex[eMutex]);
+}
+static void async_cond_wait(int eCond, int eMutex){
+ assert( eMutex==0 || eMutex==1 || eMutex==2 );
+ assert( mutex_held(eMutex) );
+ TESTONLY( primitives.aHolder[eMutex] = 0; )
+ pthread_cond_wait(&primitives.aCond[eCond], &primitives.aMutex[eMutex]);
+ TESTONLY( primitives.aHolder[eMutex] = pthread_self(); )
+}
+static void async_cond_signal(int eCond){
+ assert( mutex_held(ASYNC_MUTEX_QUEUE) );
+ pthread_cond_signal(&primitives.aCond[eCond]);
+}
+static void async_sched_yield(void){
+ sched_yield();
+}
+#endif
+/*
+** End of OS specific code.
+*************************************************************************/
+
+#define assert_mutex_is_held(X) assert( mutex_held(X) )
+
+
+#ifndef SQLITE_ASYNC_TWO_FILEHANDLES
+/* #define SQLITE_ASYNC_TWO_FILEHANDLES 0 */
+#define SQLITE_ASYNC_TWO_FILEHANDLES 1
+#endif
+
+/*
+** State information is held in the static variable "async" defined
+** as the following structure.
+**
+** Both async.ioError and async.nFile are protected by async.queueMutex.
+*/
+static struct TestAsyncStaticData {
+ AsyncWrite *pQueueFirst; /* Next write operation to be processed */
+ AsyncWrite *pQueueLast; /* Last write operation on the list */
+ AsyncLock *pLock; /* Linked list of all AsyncLock structures */
+ volatile int ioDelay; /* Extra delay between write operations */
+ volatile int eHalt; /* One of the SQLITEASYNC_HALT_XXX values */
+ volatile int bLockFiles; /* Current value of "lockfiles" parameter */
+ int ioError; /* True if an IO error has occurred */
+ int nFile; /* Number of open files (from sqlite pov) */
+} async = { 0,0,0,0,0,1,0,0 };
+
+/* Possible values of AsyncWrite.op */
+#define ASYNC_NOOP 0
+#define ASYNC_WRITE 1
+#define ASYNC_SYNC 2
+#define ASYNC_TRUNCATE 3
+#define ASYNC_CLOSE 4
+#define ASYNC_DELETE 5
+#define ASYNC_OPENEXCLUSIVE 6
+#define ASYNC_UNLOCK 7
+
+/* Names of opcodes. Used for debugging only.
+** Make sure these stay in sync with the macros above!
+*/
+static const char *azOpcodeName[] = {
+ "NOOP", "WRITE", "SYNC", "TRUNCATE", "CLOSE", "DELETE", "OPENEX", "UNLOCK"
+};
+
+/*
+** Entries on the write-op queue are instances of the AsyncWrite
+** structure, defined here.
+**
+** The interpretation of the iOffset and nByte variables varies depending
+** on the value of AsyncWrite.op:
+**
+** ASYNC_NOOP:
+** No values used.
+**
+** ASYNC_WRITE:
+** iOffset -> Offset in file to write to.
+** nByte -> Number of bytes of data to write (pointed to by zBuf).
+**
+** ASYNC_SYNC:
+** nByte -> flags to pass to sqlite3OsSync().
+**
+** ASYNC_TRUNCATE:
+** iOffset -> Size to truncate file to.
+** nByte -> Unused.
+**
+** ASYNC_CLOSE:
+** iOffset -> Unused.
+** nByte -> Unused.
+**
+** ASYNC_DELETE:
+** iOffset -> Contains the "syncDir" flag.
+** nByte -> Number of bytes of zBuf points to (file name).
+**
+** ASYNC_OPENEXCLUSIVE:
+** iOffset -> Value of "delflag".
+** nByte -> Number of bytes of zBuf points to (file name).
+**
+** ASYNC_UNLOCK:
+** nByte -> Argument to sqlite3OsUnlock().
+**
+**
+** For an ASYNC_WRITE operation, zBuf points to the data to write to the file.
+** This space is sqlite3_malloc()d along with the AsyncWrite structure in a
+** single blob, so is deleted when sqlite3_free() is called on the parent
+** structure.
+*/
+struct AsyncWrite {
+ AsyncFileData *pFileData; /* File to write data to or sync */
+ int op; /* One of ASYNC_xxx etc. */
+ sqlite_int64 iOffset; /* See above */
+ int nByte; /* See above */
+ char *zBuf; /* Data to write to file (or NULL if op!=ASYNC_WRITE) */
+ AsyncWrite *pNext; /* Next write operation (to any file) */
+};
+
+/*
+** An instance of this structure is created for each distinct open file
+** (i.e. if two handles are opened on the one file, only one of these
+** structures is allocated) and stored in the async.aLock hash table. The
+** keys for async.aLock are the full pathnames of the opened files.
+**
+** AsyncLock.pList points to the head of a linked list of AsyncFileLock
+** structures, one for each handle currently open on the file.
+**
+** If the opened file is not a main-database (the SQLITE_OPEN_MAIN_DB is
+** not passed to the sqlite3OsOpen() call), or if async.bLockFiles is
+** false, variables AsyncLock.pFile and AsyncLock.eLock are never used.
+** Otherwise, pFile is a file handle opened on the file in question and
+** used to obtain the file-system locks required by database connections
+** within this process.
+**
+** See comments above the asyncLock() function for more details on
+** the implementation of database locking used by this backend.
+*/
+struct AsyncLock {
+ char *zFile;
+ int nFile;
+ sqlite3_file *pFile;
+ int eLock;
+ AsyncFileLock *pList;
+ AsyncLock *pNext; /* Next in linked list headed by async.pLock */
+};
+
+/*
+** An instance of the following structure is allocated along with each
+** AsyncFileData structure (see AsyncFileData.lock), but is only used if the
+** file was opened with the SQLITE_OPEN_MAIN_DB.
+*/
+struct AsyncFileLock {
+ int eLock; /* Internally visible lock state (sqlite pov) */
+ int eAsyncLock; /* Lock-state with write-queue unlock */
+ AsyncFileLock *pNext;
+};
+
+/*
+** The AsyncFile structure is a subclass of sqlite3_file used for
+** asynchronous IO.
+**
+** All of the actual data for the structure is stored in the structure
+** pointed to by AsyncFile.pData, which is allocated as part of the
+** sqlite3OsOpen() using sqlite3_malloc(). The reason for this is that the
+** lifetime of the AsyncFile structure is ended by the caller after OsClose()
+** is called, but the data in AsyncFileData may be required by the
+** writer thread after that point.
+*/
+struct AsyncFile {
+ sqlite3_io_methods *pMethod;
+ AsyncFileData *pData;
+};
+struct AsyncFileData {
+ char *zName; /* Underlying OS filename - used for debugging */
+ int nName; /* Number of characters in zName */
+ sqlite3_file *pBaseRead; /* Read handle to the underlying Os file */
+ sqlite3_file *pBaseWrite; /* Write handle to the underlying Os file */
+ AsyncFileLock lock; /* Lock state for this handle */
+ AsyncLock *pLock; /* AsyncLock object for this file system entry */
+ AsyncWrite closeOp; /* Preallocated close operation */
+};
+
+/*
+** Add an entry to the end of the global write-op list. pWrite should point
+** to an AsyncWrite structure allocated using sqlite3_malloc(). The writer
+** thread will call sqlite3_free() to free the structure after the specified
+** operation has been completed.
+**
+** Once an AsyncWrite structure has been added to the list, it becomes the
+** property of the writer thread and must not be read or modified by the
+** caller.
+*/
+static void addAsyncWrite(AsyncWrite *pWrite){
+ /* We must hold the queue mutex in order to modify the queue pointers */
+ if( pWrite->op!=ASYNC_UNLOCK ){
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+ }
+
+ /* Add the record to the end of the write-op queue */
+ assert( !pWrite->pNext );
+ if( async.pQueueLast ){
+ assert( async.pQueueFirst );
+ async.pQueueLast->pNext = pWrite;
+ }else{
+ async.pQueueFirst = pWrite;
+ }
+ async.pQueueLast = pWrite;
+ ASYNC_TRACE(("PUSH %p (%s %s %d)\n", pWrite, azOpcodeName[pWrite->op],
+ pWrite->pFileData ? pWrite->pFileData->zName : "-", pWrite->iOffset));
+
+ if( pWrite->op==ASYNC_CLOSE ){
+ async.nFile--;
+ }
+
+ /* The writer thread might have been idle because there was nothing
+ ** on the write-op queue for it to do. So wake it up. */
+ async_cond_signal(ASYNC_COND_QUEUE);
+
+ /* Drop the queue mutex */
+ if( pWrite->op!=ASYNC_UNLOCK ){
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+ }
+}
+
+/*
+** Increment async.nFile in a thread-safe manner.
+*/
+static void incrOpenFileCount(void){
+ /* We must hold the queue mutex in order to modify async.nFile */
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+ if( async.nFile==0 ){
+ async.ioError = SQLITE_OK;
+ }
+ async.nFile++;
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+}
+
+/*
+** This is a utility function to allocate and populate a new AsyncWrite
+** structure and insert it (via addAsyncWrite() ) into the global list.
+*/
+static int addNewAsyncWrite(
+ AsyncFileData *pFileData,
+ int op,
+ sqlite3_int64 iOffset,
+ int nByte,
+ const char *zByte
+){
+ AsyncWrite *p;
+ if( op!=ASYNC_CLOSE && async.ioError ){
+ return async.ioError;
+ }
+ p = sqlite3_malloc(sizeof(AsyncWrite) + (zByte?nByte:0));
+ if( !p ){
+ /* The upper layer does not expect operations like OsWrite() to
+ ** return SQLITE_NOMEM. This is partly because under normal conditions
+ ** SQLite is required to do rollback without calling malloc(). So
+ ** if malloc() fails here, treat it as an I/O error. The above
+ ** layer knows how to handle that.
+ */
+ return SQLITE_IOERR;
+ }
+ p->op = op;
+ p->iOffset = iOffset;
+ p->nByte = nByte;
+ p->pFileData = pFileData;
+ p->pNext = 0;
+ if( zByte ){
+ p->zBuf = (char *)&p[1];
+ memcpy(p->zBuf, zByte, nByte);
+ }else{
+ p->zBuf = 0;
+ }
+ addAsyncWrite(p);
+ return SQLITE_OK;
+}
+
+/*
+** Close the file. This just adds an entry to the write-op list, the file is
+** not actually closed.
+*/
+static int asyncClose(sqlite3_file *pFile){
+ AsyncFileData *p = ((AsyncFile *)pFile)->pData;
+
+ /* Unlock the file, if it is locked */
+ async_mutex_enter(ASYNC_MUTEX_LOCK);
+ p->lock.eLock = 0;
+ async_mutex_leave(ASYNC_MUTEX_LOCK);
+
+ addAsyncWrite(&p->closeOp);
+ return SQLITE_OK;
+}
+
+/*
+** Implementation of sqlite3OsWrite() for asynchronous files. Instead of
+** writing to the underlying file, this function adds an entry to the end of
+** the global AsyncWrite list. Either SQLITE_OK or SQLITE_NOMEM may be
+** returned.
+*/
+static int asyncWrite(
+ sqlite3_file *pFile,
+ const void *pBuf,
+ int amt,
+ sqlite3_int64 iOff
+){
+ AsyncFileData *p = ((AsyncFile *)pFile)->pData;
+ return addNewAsyncWrite(p, ASYNC_WRITE, iOff, amt, pBuf);
+}
+
+/*
+** Read data from the file. First we read from the filesystem, then adjust
+** the contents of the buffer based on ASYNC_WRITE operations in the
+** write-op queue.
+**
+** This method holds the mutex from start to finish.
+*/
+static int asyncRead(
+ sqlite3_file *pFile,
+ void *zOut,
+ int iAmt,
+ sqlite3_int64 iOffset
+){
+ AsyncFileData *p = ((AsyncFile *)pFile)->pData;
+ int rc = SQLITE_OK;
+ sqlite3_int64 filesize = 0;
+ sqlite3_file *pBase = p->pBaseRead;
+ sqlite3_int64 iAmt64 = (sqlite3_int64)iAmt;
+
+ /* Grab the write queue mutex for the duration of the call */
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+
+ /* If an I/O error has previously occurred in this virtual file
+ ** system, then all subsequent operations fail.
+ */
+ if( async.ioError!=SQLITE_OK ){
+ rc = async.ioError;
+ goto asyncread_out;
+ }
+
+ if( pBase->pMethods ){
+ sqlite3_int64 nRead;
+ rc = pBase->pMethods->xFileSize(pBase, &filesize);
+ if( rc!=SQLITE_OK ){
+ goto asyncread_out;
+ }
+ nRead = MIN(filesize - iOffset, iAmt64);
+ if( nRead>0 ){
+ rc = pBase->pMethods->xRead(pBase, zOut, (int)nRead, iOffset);
+ ASYNC_TRACE(("READ %s %d bytes at %d\n", p->zName, nRead, iOffset));
+ }
+ }
+
+ if( rc==SQLITE_OK ){
+ AsyncWrite *pWrite;
+ char *zName = p->zName;
+
+ for(pWrite=async.pQueueFirst; pWrite; pWrite = pWrite->pNext){
+ if( pWrite->op==ASYNC_WRITE && (
+ (pWrite->pFileData==p) ||
+ (zName && pWrite->pFileData->zName==zName)
+ )){
+ sqlite3_int64 nCopy;
+ sqlite3_int64 nByte64 = (sqlite3_int64)pWrite->nByte;
+
+ /* Set variable iBeginIn to the offset in buffer pWrite->zBuf[] from
+ ** which data should be copied. Set iBeginOut to the offset within
+ ** the output buffer to which data should be copied. If either of
+ ** these offsets is a negative number, set them to 0.
+ */
+ sqlite3_int64 iBeginOut = (pWrite->iOffset-iOffset);
+ sqlite3_int64 iBeginIn = -iBeginOut;
+ if( iBeginIn<0 ) iBeginIn = 0;
+ if( iBeginOut<0 ) iBeginOut = 0;
+
+ filesize = MAX(filesize, pWrite->iOffset+nByte64);
+
+ nCopy = MIN(nByte64-iBeginIn, iAmt64-iBeginOut);
+ if( nCopy>0 ){
+ memcpy(&((char *)zOut)[iBeginOut], &pWrite->zBuf[iBeginIn], (size_t)nCopy);
+ ASYNC_TRACE(("OVERREAD %d bytes at %d\n", nCopy, iBeginOut+iOffset));
+ }
+ }
+ }
+ }
+
+asyncread_out:
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+ if( rc==SQLITE_OK && filesize<(iOffset+iAmt) ){
+ rc = SQLITE_IOERR_SHORT_READ;
+ }
+ return rc;
+}
+
+/*
+** Truncate the file to nByte bytes in length. This just adds an entry to
+** the write-op list, no IO actually takes place.
+*/
+static int asyncTruncate(sqlite3_file *pFile, sqlite3_int64 nByte){
+ AsyncFileData *p = ((AsyncFile *)pFile)->pData;
+ return addNewAsyncWrite(p, ASYNC_TRUNCATE, nByte, 0, 0);
+}
+
+/*
+** Sync the file. This just adds an entry to the write-op list, the
+** sync() is done later by sqlite3_async_flush().
+*/
+static int asyncSync(sqlite3_file *pFile, int flags){
+ AsyncFileData *p = ((AsyncFile *)pFile)->pData;
+ return addNewAsyncWrite(p, ASYNC_SYNC, 0, flags, 0);
+}
+
+/*
+** Read the size of the file. First we read the size of the file system
+** entry, then adjust for any ASYNC_WRITE or ASYNC_TRUNCATE operations
+** currently in the write-op list.
+**
+** This method holds the mutex from start to finish.
+*/
+int asyncFileSize(sqlite3_file *pFile, sqlite3_int64 *piSize){
+ AsyncFileData *p = ((AsyncFile *)pFile)->pData;
+ int rc = SQLITE_OK;
+ sqlite3_int64 s = 0;
+ sqlite3_file *pBase;
+
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+
+ /* Read the filesystem size from the base file. If pMethods is NULL, this
+ ** means the file hasn't been opened yet. In this case all relevant data
+ ** must be in the write-op queue anyway, so we can omit reading from the
+ ** file-system.
+ */
+ pBase = p->pBaseRead;
+ if( pBase->pMethods ){
+ rc = pBase->pMethods->xFileSize(pBase, &s);
+ }
+
+ if( rc==SQLITE_OK ){
+ AsyncWrite *pWrite;
+ for(pWrite=async.pQueueFirst; pWrite; pWrite = pWrite->pNext){
+ if( pWrite->op==ASYNC_DELETE
+ && p->zName
+ && strcmp(p->zName, pWrite->zBuf)==0
+ ){
+ s = 0;
+ }else if( pWrite->pFileData && (
+ (pWrite->pFileData==p)
+ || (p->zName && pWrite->pFileData->zName==p->zName)
+ )){
+ switch( pWrite->op ){
+ case ASYNC_WRITE:
+ s = MAX(pWrite->iOffset + (sqlite3_int64)(pWrite->nByte), s);
+ break;
+ case ASYNC_TRUNCATE:
+ s = MIN(s, pWrite->iOffset);
+ break;
+ }
+ }
+ }
+ *piSize = s;
+ }
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+ return rc;
+}
+
+/*
+** Lock or unlock the actual file-system entry.
+*/
+static int getFileLock(AsyncLock *pLock){
+ int rc = SQLITE_OK;
+ AsyncFileLock *pIter;
+ int eRequired = 0;
+
+ if( pLock->pFile ){
+ for(pIter=pLock->pList; pIter; pIter=pIter->pNext){
+ assert(pIter->eAsyncLock>=pIter->eLock);
+ if( pIter->eAsyncLock>eRequired ){
+ eRequired = pIter->eAsyncLock;
+ assert(eRequired>=0 && eRequired<=SQLITE_LOCK_EXCLUSIVE);
+ }
+ }
+
+ if( eRequired>pLock->eLock ){
+ rc = pLock->pFile->pMethods->xLock(pLock->pFile, eRequired);
+ if( rc==SQLITE_OK ){
+ pLock->eLock = eRequired;
+ }
+ }
+ else if( eRequired<pLock->eLock && eRequired<=SQLITE_LOCK_SHARED ){
+ rc = pLock->pFile->pMethods->xUnlock(pLock->pFile, eRequired);
+ if( rc==SQLITE_OK ){
+ pLock->eLock = eRequired;
+ }
+ }
+ }
+
+ return rc;
+}
+
+/*
+** Return the AsyncLock structure from the global async.pLock list
+** associated with the file-system entry identified by path zName
+** (a string of nName bytes). If no such structure exists, return 0.
+*/
+static AsyncLock *findLock(const char *zName, int nName){
+ AsyncLock *p = async.pLock;
+ while( p && (p->nFile!=nName || memcmp(p->zFile, zName, nName)) ){
+ p = p->pNext;
+ }
+ return p;
+}
+
+/*
+** The following two methods - asyncLock() and asyncUnlock() - are used
+** to obtain and release locks on database files opened with the
+** asynchronous backend.
+*/
+static int asyncLock(sqlite3_file *pFile, int eLock){
+ int rc = SQLITE_OK;
+ AsyncFileData *p = ((AsyncFile *)pFile)->pData;
+
+ if( p->zName ){
+ async_mutex_enter(ASYNC_MUTEX_LOCK);
+ if( p->lock.eLock<eLock ){
+ AsyncLock *pLock = p->pLock;
+ AsyncFileLock *pIter;
+ assert(pLock && pLock->pList);
+ for(pIter=pLock->pList; pIter; pIter=pIter->pNext){
+ if( pIter!=&p->lock && (
+ (eLock==SQLITE_LOCK_EXCLUSIVE && pIter->eLock>=SQLITE_LOCK_SHARED) ||
+ (eLock==SQLITE_LOCK_PENDING && pIter->eLock>=SQLITE_LOCK_RESERVED) ||
+ (eLock==SQLITE_LOCK_RESERVED && pIter->eLock>=SQLITE_LOCK_RESERVED) ||
+ (eLock==SQLITE_LOCK_SHARED && pIter->eLock>=SQLITE_LOCK_PENDING)
+ )){
+ rc = SQLITE_BUSY;
+ }
+ }
+ if( rc==SQLITE_OK ){
+ p->lock.eLock = eLock;
+ p->lock.eAsyncLock = MAX(p->lock.eAsyncLock, eLock);
+ }
+ assert(p->lock.eAsyncLock>=p->lock.eLock);
+ if( rc==SQLITE_OK ){
+ rc = getFileLock(pLock);
+ }
+ }
+ async_mutex_leave(ASYNC_MUTEX_LOCK);
+ }
+
+ ASYNC_TRACE(("LOCK %d (%s) rc=%d\n", eLock, p->zName, rc));
+ return rc;
+}
+static int asyncUnlock(sqlite3_file *pFile, int eLock){
+ int rc = SQLITE_OK;
+ AsyncFileData *p = ((AsyncFile *)pFile)->pData;
+ if( p->zName ){
+ AsyncFileLock *pLock = &p->lock;
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+ async_mutex_enter(ASYNC_MUTEX_LOCK);
+ pLock->eLock = MIN(pLock->eLock, eLock);
+ rc = addNewAsyncWrite(p, ASYNC_UNLOCK, 0, eLock, 0);
+ async_mutex_leave(ASYNC_MUTEX_LOCK);
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+ }
+ return rc;
+}
+
+/*
+** This function is called when the pager layer first opens a database file
+** and is checking for a hot-journal.
+*/
+static int asyncCheckReservedLock(sqlite3_file *pFile, int *pResOut){
+ int ret = 0;
+ AsyncFileLock *pIter;
+ AsyncFileData *p = ((AsyncFile *)pFile)->pData;
+
+ async_mutex_enter(ASYNC_MUTEX_LOCK);
+ for(pIter=p->pLock->pList; pIter; pIter=pIter->pNext){
+ if( pIter->eLock>=SQLITE_LOCK_RESERVED ){
+ ret = 1;
+ break;
+ }
+ }
+ async_mutex_leave(ASYNC_MUTEX_LOCK);
+
+ ASYNC_TRACE(("CHECK-LOCK %d (%s)\n", ret, p->zName));
+ *pResOut = ret;
+ return SQLITE_OK;
+}
+
+/*
+** sqlite3_file_control() implementation.
+*/
+static int asyncFileControl(sqlite3_file *id, int op, void *pArg){
+ switch( op ){
+ case SQLITE_FCNTL_LOCKSTATE: {
+ async_mutex_enter(ASYNC_MUTEX_LOCK);
+ *(int*)pArg = ((AsyncFile*)id)->pData->lock.eLock;
+ async_mutex_leave(ASYNC_MUTEX_LOCK);
+ return SQLITE_OK;
+ }
+ }
+ return SQLITE_NOTFOUND;
+}
+
+/*
+** Return the device characteristics and sector-size of the device. It
+** is tricky to implement these correctly, as this backend might
+** not have an open file handle at this point.
+*/
+static int asyncSectorSize(sqlite3_file *pFile){
+ UNUSED_PARAMETER(pFile);
+ return 512;
+}
+static int asyncDeviceCharacteristics(sqlite3_file *pFile){
+ UNUSED_PARAMETER(pFile);
+ return 0;
+}
+
+static int unlinkAsyncFile(AsyncFileData *pData){
+ AsyncFileLock **ppIter;
+ int rc = SQLITE_OK;
+
+ if( pData->zName ){
+ AsyncLock *pLock = pData->pLock;
+ for(ppIter=&pLock->pList; *ppIter; ppIter=&((*ppIter)->pNext)){
+ if( (*ppIter)==&pData->lock ){
+ *ppIter = pData->lock.pNext;
+ break;
+ }
+ }
+ if( !pLock->pList ){
+ AsyncLock **pp;
+ if( pLock->pFile ){
+ pLock->pFile->pMethods->xClose(pLock->pFile);
+ }
+ for(pp=&async.pLock; *pp!=pLock; pp=&((*pp)->pNext));
+ *pp = pLock->pNext;
+ sqlite3_free(pLock);
+ }else{
+ rc = getFileLock(pLock);
+ }
+ }
+
+ return rc;
+}
+
+/*
+** The parameter passed to this function is a copy of a 'flags' parameter
+** passed to this modules xOpen() method. This function returns true
+** if the file should be opened asynchronously, or false if it should
+** be opened immediately.
+**
+** If the file is to be opened asynchronously, then asyncOpen() will add
+** an entry to the event queue and the file will not actually be opened
+** until the event is processed. Otherwise, the file is opened directly
+** by the caller.
+*/
+static int doAsynchronousOpen(int flags){
+ return (flags&SQLITE_OPEN_CREATE) && (
+ (flags&SQLITE_OPEN_MAIN_JOURNAL) ||
+ (flags&SQLITE_OPEN_TEMP_JOURNAL) ||
+ (flags&SQLITE_OPEN_DELETEONCLOSE)
+ );
+}
+
+/*
+** Open a file.
+*/
+static int asyncOpen(
+ sqlite3_vfs *pAsyncVfs,
+ const char *zName,
+ sqlite3_file *pFile,
+ int flags,
+ int *pOutFlags
+){
+ static sqlite3_io_methods async_methods = {
+ 1, /* iVersion */
+ asyncClose, /* xClose */
+ asyncRead, /* xRead */
+ asyncWrite, /* xWrite */
+ asyncTruncate, /* xTruncate */
+ asyncSync, /* xSync */
+ asyncFileSize, /* xFileSize */
+ asyncLock, /* xLock */
+ asyncUnlock, /* xUnlock */
+ asyncCheckReservedLock, /* xCheckReservedLock */
+ asyncFileControl, /* xFileControl */
+ asyncSectorSize, /* xSectorSize */
+ asyncDeviceCharacteristics /* xDeviceCharacteristics */
+ };
+
+ sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
+ AsyncFile *p = (AsyncFile *)pFile;
+ int nName = 0;
+ int rc = SQLITE_OK;
+ int nByte;
+ AsyncFileData *pData;
+ AsyncLock *pLock = 0;
+ char *z;
+ int isAsyncOpen = doAsynchronousOpen(flags);
+
+ /* If zName is NULL, then the upper layer is requesting an anonymous file.
+ ** Otherwise, allocate enough space to make a copy of the file name (along
+ ** with the second nul-terminator byte required by xOpen).
+ */
+ if( zName ){
+ nName = (int)strlen(zName);
+ }
+
+ nByte = (
+ sizeof(AsyncFileData) + /* AsyncFileData structure */
+ 2 * pVfs->szOsFile + /* AsyncFileData.pBaseRead and pBaseWrite */
+ nName + 2 /* AsyncFileData.zName */
+ );
+ z = sqlite3_malloc(nByte);
+ if( !z ){
+ return SQLITE_NOMEM;
+ }
+ memset(z, 0, nByte);
+ pData = (AsyncFileData*)z;
+ z += sizeof(pData[0]);
+ pData->pBaseRead = (sqlite3_file*)z;
+ z += pVfs->szOsFile;
+ pData->pBaseWrite = (sqlite3_file*)z;
+ pData->closeOp.pFileData = pData;
+ pData->closeOp.op = ASYNC_CLOSE;
+
+ if( zName ){
+ z += pVfs->szOsFile;
+ pData->zName = z;
+ pData->nName = nName;
+ memcpy(pData->zName, zName, nName);
+ }
+
+ if( !isAsyncOpen ){
+ int flagsout;
+ rc = pVfs->xOpen(pVfs, pData->zName, pData->pBaseRead, flags, &flagsout);
+ if( rc==SQLITE_OK
+ && (flagsout&SQLITE_OPEN_READWRITE)
+ && (flags&SQLITE_OPEN_EXCLUSIVE)==0
+ ){
+ rc = pVfs->xOpen(pVfs, pData->zName, pData->pBaseWrite, flags, 0);
+ }
+ if( pOutFlags ){
+ *pOutFlags = flagsout;
+ }
+ }
+
+ async_mutex_enter(ASYNC_MUTEX_LOCK);
+
+ if( zName && rc==SQLITE_OK ){
+ pLock = findLock(pData->zName, pData->nName);
+ if( !pLock ){
+ int nByte = pVfs->szOsFile + sizeof(AsyncLock) + pData->nName + 1;
+ pLock = (AsyncLock *)sqlite3_malloc(nByte);
+ if( pLock ){
+ memset(pLock, 0, nByte);
+ if( async.bLockFiles && (flags&SQLITE_OPEN_MAIN_DB) ){
+ pLock->pFile = (sqlite3_file *)&pLock[1];
+ rc = pVfs->xOpen(pVfs, pData->zName, pLock->pFile, flags, 0);
+ if( rc!=SQLITE_OK ){
+ sqlite3_free(pLock);
+ pLock = 0;
+ }
+ }
+ if( pLock ){
+ pLock->nFile = pData->nName;
+ pLock->zFile = &((char *)(&pLock[1]))[pVfs->szOsFile];
+ memcpy(pLock->zFile, pData->zName, pLock->nFile);
+ pLock->pNext = async.pLock;
+ async.pLock = pLock;
+ }
+ }else{
+ rc = SQLITE_NOMEM;
+ }
+ }
+ }
+
+ if( rc==SQLITE_OK ){
+ p->pMethod = &async_methods;
+ p->pData = pData;
+
+ /* Link AsyncFileData.lock into the linked list of
+ ** AsyncFileLock structures for this file.
+ */
+ if( zName ){
+ pData->lock.pNext = pLock->pList;
+ pLock->pList = &pData->lock;
+ pData->zName = pLock->zFile;
+ }
+ }else{
+ if( pData->pBaseRead->pMethods ){
+ pData->pBaseRead->pMethods->xClose(pData->pBaseRead);
+ }
+ if( pData->pBaseWrite->pMethods ){
+ pData->pBaseWrite->pMethods->xClose(pData->pBaseWrite);
+ }
+ sqlite3_free(pData);
+ }
+
+ async_mutex_leave(ASYNC_MUTEX_LOCK);
+
+ if( rc==SQLITE_OK ){
+ pData->pLock = pLock;
+ }
+
+ if( rc==SQLITE_OK && isAsyncOpen ){
+ rc = addNewAsyncWrite(pData, ASYNC_OPENEXCLUSIVE, (sqlite3_int64)flags,0,0);
+ if( rc==SQLITE_OK ){
+ if( pOutFlags ) *pOutFlags = flags;
+ }else{
+ async_mutex_enter(ASYNC_MUTEX_LOCK);
+ unlinkAsyncFile(pData);
+ async_mutex_leave(ASYNC_MUTEX_LOCK);
+ sqlite3_free(pData);
+ }
+ }
+ if( rc!=SQLITE_OK ){
+ p->pMethod = 0;
+ }else{
+ incrOpenFileCount();
+ }
+
+ return rc;
+}
+
+/*
+** Implementation of sqlite3OsDelete. Add an entry to the end of the
+** write-op queue to perform the delete.
+*/
+static int asyncDelete(sqlite3_vfs *pAsyncVfs, const char *z, int syncDir){
+ UNUSED_PARAMETER(pAsyncVfs);
+ return addNewAsyncWrite(0, ASYNC_DELETE, syncDir, (int)strlen(z)+1, z);
+}
+
+/*
+** Implementation of sqlite3OsAccess. This method holds the mutex from
+** start to finish.
+*/
+static int asyncAccess(
+ sqlite3_vfs *pAsyncVfs,
+ const char *zName,
+ int flags,
+ int *pResOut
+){
+ int rc;
+ int ret;
+ AsyncWrite *p;
+ sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
+
+ assert(flags==SQLITE_ACCESS_READWRITE
+ || flags==SQLITE_ACCESS_READ
+ || flags==SQLITE_ACCESS_EXISTS
+ );
+
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+ rc = pVfs->xAccess(pVfs, zName, flags, &ret);
+ if( rc==SQLITE_OK && flags==SQLITE_ACCESS_EXISTS ){
+ for(p=async.pQueueFirst; p; p = p->pNext){
+ if( p->op==ASYNC_DELETE && 0==strcmp(p->zBuf, zName) ){
+ ret = 0;
+ }else if( p->op==ASYNC_OPENEXCLUSIVE
+ && p->pFileData->zName
+ && 0==strcmp(p->pFileData->zName, zName)
+ ){
+ ret = 1;
+ }
+ }
+ }
+ ASYNC_TRACE(("ACCESS(%s): %s = %d\n",
+ flags==SQLITE_ACCESS_READWRITE?"read-write":
+ flags==SQLITE_ACCESS_READ?"read":"exists"
+ , zName, ret)
+ );
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+ *pResOut = ret;
+ return rc;
+}
+
+/*
+** Fill in zPathOut with the full path to the file identified by zPath.
+*/
+static int asyncFullPathname(
+ sqlite3_vfs *pAsyncVfs,
+ const char *zPath,
+ int nPathOut,
+ char *zPathOut
+){
+ int rc;
+ sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
+ rc = pVfs->xFullPathname(pVfs, zPath, nPathOut, zPathOut);
+
+ /* Because of the way intra-process file locking works, this backend
+ ** needs to return a canonical path. The following block assumes the
+ ** file-system uses unix style paths.
+ */
+ if( rc==SQLITE_OK ){
+ int i, j;
+ char *z = zPathOut;
+ int n = (int)strlen(z);
+ while( n>1 && z[n-1]=='/' ){ n--; }
+ for(i=j=0; i<n; i++){
+ if( z[i]=='/' ){
+ if( z[i+1]=='/' ) continue;
+ if( z[i+1]=='.' && i+2<n && z[i+2]=='/' ){
+ i += 1;
+ continue;
+ }
+ if( z[i+1]=='.' && i+3<n && z[i+2]=='.' && z[i+3]=='/' ){
+ while( j>0 && z[j-1]!='/' ){ j--; }
+ if( j>0 ){ j--; }
+ i += 2;
+ continue;
+ }
+ }
+ z[j++] = z[i];
+ }
+ z[j] = 0;
+ }
+
+ return rc;
+}
+static void *asyncDlOpen(sqlite3_vfs *pAsyncVfs, const char *zPath){
+ sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
+ return pVfs->xDlOpen(pVfs, zPath);
+}
+static void asyncDlError(sqlite3_vfs *pAsyncVfs, int nByte, char *zErrMsg){
+ sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
+ pVfs->xDlError(pVfs, nByte, zErrMsg);
+}
+static void (*asyncDlSym(
+ sqlite3_vfs *pAsyncVfs,
+ void *pHandle,
+ const char *zSymbol
+))(void){
+ sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
+ return pVfs->xDlSym(pVfs, pHandle, zSymbol);
+}
+static void asyncDlClose(sqlite3_vfs *pAsyncVfs, void *pHandle){
+ sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
+ pVfs->xDlClose(pVfs, pHandle);
+}
+static int asyncRandomness(sqlite3_vfs *pAsyncVfs, int nByte, char *zBufOut){
+ sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
+ return pVfs->xRandomness(pVfs, nByte, zBufOut);
+}
+static int asyncSleep(sqlite3_vfs *pAsyncVfs, int nMicro){
+ sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
+ return pVfs->xSleep(pVfs, nMicro);
+}
+static int asyncCurrentTime(sqlite3_vfs *pAsyncVfs, double *pTimeOut){
+ sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
+ return pVfs->xCurrentTime(pVfs, pTimeOut);
+}
+
+static sqlite3_vfs async_vfs = {
+ 1, /* iVersion */
+ sizeof(AsyncFile), /* szOsFile */
+ 0, /* mxPathname */
+ 0, /* pNext */
+ SQLITEASYNC_VFSNAME, /* zName */
+ 0, /* pAppData */
+ asyncOpen, /* xOpen */
+ asyncDelete, /* xDelete */
+ asyncAccess, /* xAccess */
+ asyncFullPathname, /* xFullPathname */
+ asyncDlOpen, /* xDlOpen */
+ asyncDlError, /* xDlError */
+ asyncDlSym, /* xDlSym */
+ asyncDlClose, /* xDlClose */
+ asyncRandomness, /* xDlError */
+ asyncSleep, /* xDlSym */
+ asyncCurrentTime /* xDlClose */
+};
+
+/*
+** This procedure runs in a separate thread, reading messages off of the
+** write queue and processing them one by one.
+**
+** If async.writerHaltNow is true, then this procedure exits
+** after processing a single message.
+**
+** If async.writerHaltWhenIdle is true, then this procedure exits when
+** the write queue is empty.
+**
+** If both of the above variables are false, this procedure runs
+** indefinately, waiting for operations to be added to the write queue
+** and processing them in the order in which they arrive.
+**
+** An artifical delay of async.ioDelay milliseconds is inserted before
+** each write operation in order to simulate the effect of a slow disk.
+**
+** Only one instance of this procedure may be running at a time.
+*/
+static void asyncWriterThread(void){
+ sqlite3_vfs *pVfs = (sqlite3_vfs *)(async_vfs.pAppData);
+ AsyncWrite *p = 0;
+ int rc = SQLITE_OK;
+ int holdingMutex = 0;
+
+ async_mutex_enter(ASYNC_MUTEX_WRITER);
+
+ while( async.eHalt!=SQLITEASYNC_HALT_NOW ){
+ int doNotFree = 0;
+ sqlite3_file *pBase = 0;
+
+ if( !holdingMutex ){
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+ }
+ while( (p = async.pQueueFirst)==0 ){
+ if( async.eHalt!=SQLITEASYNC_HALT_NEVER ){
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+ break;
+ }else{
+ ASYNC_TRACE(("IDLE\n"));
+ async_cond_wait(ASYNC_COND_QUEUE, ASYNC_MUTEX_QUEUE);
+ ASYNC_TRACE(("WAKEUP\n"));
+ }
+ }
+ if( p==0 ) break;
+ holdingMutex = 1;
+
+ /* Right now this thread is holding the mutex on the write-op queue.
+ ** Variable 'p' points to the first entry in the write-op queue. In
+ ** the general case, we hold on to the mutex for the entire body of
+ ** the loop.
+ **
+ ** However in the cases enumerated below, we relinquish the mutex,
+ ** perform the IO, and then re-request the mutex before removing 'p' from
+ ** the head of the write-op queue. The idea is to increase concurrency with
+ ** sqlite threads.
+ **
+ ** * An ASYNC_CLOSE operation.
+ ** * An ASYNC_OPENEXCLUSIVE operation. For this one, we relinquish
+ ** the mutex, call the underlying xOpenExclusive() function, then
+ ** re-aquire the mutex before seting the AsyncFile.pBaseRead
+ ** variable.
+ ** * ASYNC_SYNC and ASYNC_WRITE operations, if
+ ** SQLITE_ASYNC_TWO_FILEHANDLES was set at compile time and two
+ ** file-handles are open for the particular file being "synced".
+ */
+ if( async.ioError!=SQLITE_OK && p->op!=ASYNC_CLOSE ){
+ p->op = ASYNC_NOOP;
+ }
+ if( p->pFileData ){
+ pBase = p->pFileData->pBaseWrite;
+ if(
+ p->op==ASYNC_CLOSE ||
+ p->op==ASYNC_OPENEXCLUSIVE ||
+ (pBase->pMethods && (p->op==ASYNC_SYNC || p->op==ASYNC_WRITE) )
+ ){
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+ holdingMutex = 0;
+ }
+ if( !pBase->pMethods ){
+ pBase = p->pFileData->pBaseRead;
+ }
+ }
+
+ switch( p->op ){
+ case ASYNC_NOOP:
+ break;
+
+ case ASYNC_WRITE:
+ assert( pBase );
+ ASYNC_TRACE(("WRITE %s %d bytes at %d\n",
+ p->pFileData->zName, p->nByte, p->iOffset));
+ rc = pBase->pMethods->xWrite(pBase, (void *)(p->zBuf), p->nByte, p->iOffset);
+ break;
+
+ case ASYNC_SYNC:
+ assert( pBase );
+ ASYNC_TRACE(("SYNC %s\n", p->pFileData->zName));
+ rc = pBase->pMethods->xSync(pBase, p->nByte);
+ break;
+
+ case ASYNC_TRUNCATE:
+ assert( pBase );
+ ASYNC_TRACE(("TRUNCATE %s to %d bytes\n",
+ p->pFileData->zName, p->iOffset));
+ rc = pBase->pMethods->xTruncate(pBase, p->iOffset);
+ break;
+
+ case ASYNC_CLOSE: {
+ AsyncFileData *pData = p->pFileData;
+ ASYNC_TRACE(("CLOSE %s\n", p->pFileData->zName));
+ if( pData->pBaseWrite->pMethods ){
+ pData->pBaseWrite->pMethods->xClose(pData->pBaseWrite);
+ }
+ if( pData->pBaseRead->pMethods ){
+ pData->pBaseRead->pMethods->xClose(pData->pBaseRead);
+ }
+
+ /* Unlink AsyncFileData.lock from the linked list of AsyncFileLock
+ ** structures for this file. Obtain the async.lockMutex mutex
+ ** before doing so.
+ */
+ async_mutex_enter(ASYNC_MUTEX_LOCK);
+ rc = unlinkAsyncFile(pData);
+ async_mutex_leave(ASYNC_MUTEX_LOCK);
+
+ if( !holdingMutex ){
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+ holdingMutex = 1;
+ }
+ assert_mutex_is_held(ASYNC_MUTEX_QUEUE);
+ async.pQueueFirst = p->pNext;
+ sqlite3_free(pData);
+ doNotFree = 1;
+ break;
+ }
+
+ case ASYNC_UNLOCK: {
+ AsyncWrite *pIter;
+ AsyncFileData *pData = p->pFileData;
+ int eLock = p->nByte;
+
+ /* When a file is locked by SQLite using the async backend, it is
+ ** locked within the 'real' file-system synchronously. When it is
+ ** unlocked, an ASYNC_UNLOCK event is added to the write-queue to
+ ** unlock the file asynchronously. The design of the async backend
+ ** requires that the 'real' file-system file be locked from the
+ ** time that SQLite first locks it (and probably reads from it)
+ ** until all asynchronous write events that were scheduled before
+ ** SQLite unlocked the file have been processed.
+ **
+ ** This is more complex if SQLite locks and unlocks the file multiple
+ ** times in quick succession. For example, if SQLite does:
+ **
+ ** lock, write, unlock, lock, write, unlock
+ **
+ ** Each "lock" operation locks the file immediately. Each "write"
+ ** and "unlock" operation adds an event to the event queue. If the
+ ** second "lock" operation is performed before the first "unlock"
+ ** operation has been processed asynchronously, then the first
+ ** "unlock" cannot be safely processed as is, since this would mean
+ ** the file was unlocked when the second "write" operation is
+ ** processed. To work around this, when processing an ASYNC_UNLOCK
+ ** operation, SQLite:
+ **
+ ** 1) Unlocks the file to the minimum of the argument passed to
+ ** the xUnlock() call and the current lock from SQLite's point
+ ** of view, and
+ **
+ ** 2) Only unlocks the file at all if this event is the last
+ ** ASYNC_UNLOCK event on this file in the write-queue.
+ */
+ assert( holdingMutex==1 );
+ assert( async.pQueueFirst==p );
+ for(pIter=async.pQueueFirst->pNext; pIter; pIter=pIter->pNext){
+ if( pIter->pFileData==pData && pIter->op==ASYNC_UNLOCK ) break;
+ }
+ if( !pIter ){
+ async_mutex_enter(ASYNC_MUTEX_LOCK);
+ pData->lock.eAsyncLock = MIN(
+ pData->lock.eAsyncLock, MAX(pData->lock.eLock, eLock)
+ );
+ assert(pData->lock.eAsyncLock>=pData->lock.eLock);
+ rc = getFileLock(pData->pLock);
+ async_mutex_leave(ASYNC_MUTEX_LOCK);
+ }
+ break;
+ }
+
+ case ASYNC_DELETE:
+ ASYNC_TRACE(("DELETE %s\n", p->zBuf));
+ rc = pVfs->xDelete(pVfs, p->zBuf, (int)p->iOffset);
+ break;
+
+ case ASYNC_OPENEXCLUSIVE: {
+ int flags = (int)p->iOffset;
+ AsyncFileData *pData = p->pFileData;
+ ASYNC_TRACE(("OPEN %s flags=%d\n", p->zBuf, (int)p->iOffset));
+ assert(pData->pBaseRead->pMethods==0 && pData->pBaseWrite->pMethods==0);
+ rc = pVfs->xOpen(pVfs, pData->zName, pData->pBaseRead, flags, 0);
+ assert( holdingMutex==0 );
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+ holdingMutex = 1;
+ break;
+ }
+
+ default: assert(!"Illegal value for AsyncWrite.op");
+ }
+
+ /* If we didn't hang on to the mutex during the IO op, obtain it now
+ ** so that the AsyncWrite structure can be safely removed from the
+ ** global write-op queue.
+ */
+ if( !holdingMutex ){
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+ holdingMutex = 1;
+ }
+ /* ASYNC_TRACE(("UNLINK %p\n", p)); */
+ if( p==async.pQueueLast ){
+ async.pQueueLast = 0;
+ }
+ if( !doNotFree ){
+ assert_mutex_is_held(ASYNC_MUTEX_QUEUE);
+ async.pQueueFirst = p->pNext;
+ sqlite3_free(p);
+ }
+ assert( holdingMutex );
+
+ /* An IO error has occurred. We cannot report the error back to the
+ ** connection that requested the I/O since the error happened
+ ** asynchronously. The connection has already moved on. There
+ ** really is nobody to report the error to.
+ **
+ ** The file for which the error occurred may have been a database or
+ ** journal file. Regardless, none of the currently queued operations
+ ** associated with the same database should now be performed. Nor should
+ ** any subsequently requested IO on either a database or journal file
+ ** handle for the same database be accepted until the main database
+ ** file handle has been closed and reopened.
+ **
+ ** Furthermore, no further IO should be queued or performed on any file
+ ** handle associated with a database that may have been part of a
+ ** multi-file transaction that included the database associated with
+ ** the IO error (i.e. a database ATTACHed to the same handle at some
+ ** point in time).
+ */
+ if( rc!=SQLITE_OK ){
+ async.ioError = rc;
+ }
+
+ if( async.ioError && !async.pQueueFirst ){
+ async_mutex_enter(ASYNC_MUTEX_LOCK);
+ if( 0==async.pLock ){
+ async.ioError = SQLITE_OK;
+ }
+ async_mutex_leave(ASYNC_MUTEX_LOCK);
+ }
+
+ /* Drop the queue mutex before continuing to the next write operation
+ ** in order to give other threads a chance to work with the write queue.
+ */
+ if( !async.pQueueFirst || !async.ioError ){
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+ holdingMutex = 0;
+ if( async.ioDelay>0 ){
+ pVfs->xSleep(pVfs, async.ioDelay*1000);
+ }else{
+ async_sched_yield();
+ }
+ }
+ }
+
+ async_mutex_leave(ASYNC_MUTEX_WRITER);
+ return;
+}
+
+/*
+** Install the asynchronous VFS.
+*/
+int sqlite3async_initialize(const char *zParent, int isDefault){
+ int rc = SQLITE_OK;
+ if( async_vfs.pAppData==0 ){
+ sqlite3_vfs *pParent = sqlite3_vfs_find(zParent);
+ if( !pParent || async_os_initialize() ){
+ rc = SQLITE_ERROR;
+ }else if( SQLITE_OK!=(rc = sqlite3_vfs_register(&async_vfs, isDefault)) ){
+ async_os_shutdown();
+ }else{
+ async_vfs.pAppData = (void *)pParent;
+ async_vfs.mxPathname = ((sqlite3_vfs *)async_vfs.pAppData)->mxPathname;
+ }
+ }
+ return rc;
+}
+
+/*
+** Uninstall the asynchronous VFS.
+*/
+void sqlite3async_shutdown(void){
+ if( async_vfs.pAppData ){
+ async_os_shutdown();
+ sqlite3_vfs_unregister((sqlite3_vfs *)&async_vfs);
+ async_vfs.pAppData = 0;
+ }
+}
+
+/*
+** Process events on the write-queue.
+*/
+void sqlite3async_run(void){
+ asyncWriterThread();
+}
+
+/*
+** Control/configure the asynchronous IO system.
+*/
+int sqlite3async_control(int op, ...){
+ va_list ap;
+ va_start(ap, op);
+ switch( op ){
+ case SQLITEASYNC_HALT: {
+ int eWhen = va_arg(ap, int);
+ if( eWhen!=SQLITEASYNC_HALT_NEVER
+ && eWhen!=SQLITEASYNC_HALT_NOW
+ && eWhen!=SQLITEASYNC_HALT_IDLE
+ ){
+ return SQLITE_MISUSE;
+ }
+ async.eHalt = eWhen;
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+ async_cond_signal(ASYNC_COND_QUEUE);
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+ break;
+ }
+
+ case SQLITEASYNC_DELAY: {
+ int iDelay = va_arg(ap, int);
+ if( iDelay<0 ){
+ return SQLITE_MISUSE;
+ }
+ async.ioDelay = iDelay;
+ break;
+ }
+
+ case SQLITEASYNC_LOCKFILES: {
+ int bLock = va_arg(ap, int);
+ async_mutex_enter(ASYNC_MUTEX_QUEUE);
+ if( async.nFile || async.pQueueFirst ){
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+ return SQLITE_MISUSE;
+ }
+ async.bLockFiles = bLock;
+ async_mutex_leave(ASYNC_MUTEX_QUEUE);
+ break;
+ }
+
+ case SQLITEASYNC_GET_HALT: {
+ int *peWhen = va_arg(ap, int *);
+ *peWhen = async.eHalt;
+ break;
+ }
+ case SQLITEASYNC_GET_DELAY: {
+ int *piDelay = va_arg(ap, int *);
+ *piDelay = async.ioDelay;
+ break;
+ }
+ case SQLITEASYNC_GET_LOCKFILES: {
+ int *piDelay = va_arg(ap, int *);
+ *piDelay = async.bLockFiles;
+ break;
+ }
+
+ default:
+ return SQLITE_ERROR;
+ }
+ return SQLITE_OK;
+}
+
+#endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_ASYNCIO) */
+