--- /dev/null
+/*
+** 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.
+**
+*************************************************************************
+**
+** This file contains an example implementation of an asynchronous IO
+** backend for SQLite. It is used to test that the concept of asynchronous
+** IO in SQLite is valid.
+*/
+
+#include "sqliteInt.h"
+#include "os.h"
+#include <tcl.h>
+
+#ifndef THREADSAFE
+# define THREADSAFE 0
+#endif
+
+/*
+** This test uses pthreads and hence only works on unix and with
+** a threadsafe build of SQLite.
+*/
+#if OS_UNIX && THREADSAFE && defined(SQLITE_ENABLE_REDEF_IO)
+
+#include <pthread.h>
+#include <sched.h>
+
+#define MIN(x,y) ((x)<(y)?(x):(y))
+#define MAX(x,y) ((x)>(y)?(x):(y))
+
+typedef struct AsyncWrite AsyncWrite;
+typedef struct AsyncFile AsyncFile;
+
+#if 0
+# define TRACE(X,Y) \
+ fprintf(stderr,"THRD=%d: ", (int)pthread_self()); \
+ fprintf(stderr,X,Y);
+#else
+# define TRACE(X,Y) /* noop */
+#endif
+
+/*
+** TODO:
+** * File locks...
+*/
+
+/*
+** THREAD SAFETY NOTES
+**
+** Basic rules:
+**
+** * Both read and write access to the global write-op queue must be
+** protected by the async.queueMutex.
+**
+** * The file handles from the underlying system are assumed not to
+** be thread safe.
+**
+** * See the last paragraph under "sqlite3_async_flush() Threads" for
+** an assumption to do with file-handle synchronization by the Os.
+**
+** File system operations (invoked by SQLite thread):
+**
+** xOpenXXX (three versions)
+** xDelete
+** xFileExists
+** xSyncDirectory
+**
+** File handle operations (invoked by SQLite thread):
+**
+** The following operations add an entry to the global write-op list. They
+** prepare the entry, acquire the mutex momentarily while list pointers are
+** manipulated to insert the new entry, and release the mutex.
+**
+** asyncWrite, asyncClose, asyncTruncate, asyncSync,
+** asyncSetFullSync, asyncOpenDirectory.
+**
+** Read operations. Both of these read from both the underlying file and
+** the write-op list. So we grab the mutex for the whole call (even
+** while performing a blocking read on the file).
+**
+** asyncRead, asyncFileSize.
+**
+** These locking primitives become no-ops. Files are always opened for
+** exclusive access when using this IO backend:
+**
+** asyncLock, asyncUnlock, asyncLockState, asyncCheckReservedLock
+**
+** The sqlite3OsFileHandle() function is currently only used when
+** debugging the pager module. Unless sqlite3OsClose() is called on the
+** file (shouldn't be possible for other reasons), the underlying
+** implementations are safe to call without grabbing any mutex. So we just
+** go ahead and call it no matter what any other thread is doing.
+**
+** asyncFileHandle.
+**
+** Calling this method just manipulates the AsyncFile.iOffset variable.
+** Since this variable is never accessed by writer thread, this
+** function does not require the mutex. Actual calls to OsSeek() take
+** place just before OsWrite() or OsRead(), which are always protected by
+** the mutex.
+**
+** asyncSeek.
+**
+** 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 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 follows:
+*/
+static struct TestAsyncStaticData {
+ pthread_mutex_t queueMutex; /* Mutex for access to write operation queue */
+ pthread_mutex_t writerMutex; /* Prevents multiple writer threads */
+ pthread_cond_t queueSignal; /* For waking up sleeping writer thread */
+ pthread_cond_t emptySignal; /* Notify when the write queue is empty */
+ AsyncWrite *pQueueFirst; /* Next write operation to be processed */
+ AsyncWrite *pQueueLast; /* Last write operation on the list */
+ volatile int ioDelay; /* Extra delay between write operations */
+ volatile int writerHaltWhenIdle; /* Writer thread halts when queue empty */
+ volatile int writerHaltNow; /* Writer thread halts after next op */
+} async = {
+ PTHREAD_MUTEX_INITIALIZER,
+ PTHREAD_MUTEX_INITIALIZER,
+ PTHREAD_COND_INITIALIZER,
+ PTHREAD_COND_INITIALIZER,
+};
+
+/* Possible values of AsyncWrite.op */
+#define ASYNC_WRITE 1
+#define ASYNC_SYNC 2
+#define ASYNC_TRUNCATE 3
+#define ASYNC_CLOSE 4
+#define ASYNC_OPENDIRECTORY 5
+#define ASYNC_SETFULLSYNC 6
+
+#define ASYNC_DELETE 7
+#define ASYNC_OPENEXCLUSIVE 8
+#define ASYNC_SYNCDIRECTORY 9
+
+/*
+** The interpretation of the iOffset and nByte variables varies depending
+** on the value of AsyncWrite.op:
+**
+** ASYNC_WRITE:
+** iOffset -> Offset in file to write to.
+** nByte -> Number of bytes of data to write (pointed to by zBuf).
+**
+** ASYNC_SYNC:
+** iOffset -> Unused.
+** nByte -> Value of "fullsync" flag to pass to sqlite3OsSync().
+**
+** ASYNC_TRUNCATE:
+** iOffset -> Size to truncate file to.
+** nByte -> Unused.
+**
+** ASYNC_CLOSE:
+** iOffset -> Unused.
+** nByte -> Unused.
+**
+** ASYNC_OPENDIRECTORY:
+** iOffset -> Unused.
+** nByte -> Number of bytes of zBuf points to (directory name).
+**
+** ASYNC_SETFULLSYNC:
+** iOffset -> Unused.
+** nByte -> New value for the full-sync flag.
+**
+**
+** ASYNC_DELETE:
+** iOffset -> Unused.
+** 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).
+**
+** For an ASYNC_WRITE operation, zBuf points to the data to write to the file.
+** This space is sqliteMalloc()d along with the AsyncWrite structure in a
+** single blob, so is deleted when sqliteFree() is called on the parent
+** structure.
+*/
+struct AsyncWrite {
+ AsyncFile *pFile; /* File to write data to or sync */
+ int op; /* One of ASYNC_xxx etc. */
+ i64 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) */
+};
+
+/*
+** The AsyncFile structure is a subclass of OsFile used for asynchronous IO.
+*/
+struct AsyncFile {
+ IoMethod *pMethod; /* Must be first */
+ i64 iOffset; /* Current seek() offset in file */
+ OsFile *pBaseRead; /* Read handle to the underlying Os file */
+ OsFile *pBaseWrite; /* Write handle to the underlying Os file */
+};
+
+/*
+** Add an entry to the end of the global write-op list. pWrite should point
+** to an AsyncWrite structure allocated using sqliteMalloc(). A future call
+** to sqlite3_async_flush() is responsible for calling sqliteFree().
+**
+** Once an AsyncWrite structure has been added to the list, it must not be
+** read or modified by the caller (in case another thread calls
+** sqlite3_async_flush() ).
+*/
+static void addAsyncWrite(AsyncWrite *pWrite){
+ pthread_mutex_lock(&async.queueMutex);
+ assert( !pWrite->pNext );
+ if( async.pQueueLast ){
+ assert( async.pQueueFirst );
+ async.pQueueLast->pNext = pWrite;
+ }else{
+ async.pQueueFirst = pWrite;
+ }
+ async.pQueueLast = pWrite;
+ TRACE("PUSH %p\n", pWrite);
+ pthread_mutex_unlock(&async.queueMutex);
+ pthread_cond_signal(&async.queueSignal);
+}
+
+/*
+** 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(
+ AsyncFile *pFile,
+ int op,
+ i64 iOffset,
+ int nByte,
+ const char *zByte
+){
+ AsyncWrite *p = sqlite3OsMalloc(sizeof(AsyncWrite) + (zByte?nByte:0));
+ if( !p ){
+ return SQLITE_NOMEM;
+ }
+ p->op = op;
+ p->iOffset = iOffset;
+ p->nByte = nByte;
+ p->pFile = pFile;
+ 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(OsFile **pId){
+ return addNewAsyncWrite((AsyncFile *)*pId, ASYNC_CLOSE, 0, 0, 0);
+}
+
+/*
+** 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(OsFile *id, const void *pBuf, int amt){
+ AsyncFile *pFile = (AsyncFile *)id;
+ int rc = addNewAsyncWrite(pFile, ASYNC_WRITE, pFile->iOffset, amt, pBuf);
+ pFile->iOffset += (i64)amt;
+ 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(OsFile *id, i64 nByte){
+ return addNewAsyncWrite((AsyncFile *)id, ASYNC_TRUNCATE, nByte, 0, 0);
+}
+
+/*
+** Open the directory identified by zName and associate it with the
+** specified file. This just adds an entry to the write-op list, the
+** directory is opened later by sqlite3_async_flush().
+*/
+static int asyncOpenDirectory(OsFile *id, const char *zName){
+ AsyncFile *pFile = (AsyncFile *)id;
+ return addNewAsyncWrite(pFile, ASYNC_OPENDIRECTORY, 0, strlen(zName)+1,zName);
+}
+
+/*
+** 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(OsFile *id, int fullsync){
+ return addNewAsyncWrite((AsyncFile *)id, ASYNC_SYNC, 0, fullsync, 0);
+}
+
+/*
+** Set (or clear) the full-sync flag on the underlying file. This operation
+** is queued and performed later by sqlite3_async_flush().
+*/
+static void asyncSetFullSync(OsFile *id, int value){
+ addNewAsyncWrite((AsyncFile *)id, ASYNC_SETFULLSYNC, 0, value, 0);
+}
+
+/*
+** 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. Todo: Do we need to think about ASYNC_TRUNCATE in
+** this method as well?
+**
+** This method holds the mutex from start to finish.
+*/
+static int asyncRead(OsFile *id, void *obuf, int amt){
+ int rc = SQLITE_OK;
+ i64 filesize;
+ int nRead;
+ AsyncFile *pFile = (AsyncFile *)id;
+
+ /* Grab the write queue mutex for the duration of the call */
+ pthread_mutex_lock(&async.queueMutex);
+
+ if( pFile->pBaseRead ){
+ rc = sqlite3OsFileSize(pFile->pBaseRead, &filesize);
+ if( rc!=SQLITE_OK ){
+ goto asyncread_out;
+ }
+ rc = sqlite3OsSeek(pFile->pBaseRead, pFile->iOffset);
+ if( rc!=SQLITE_OK ){
+ goto asyncread_out;
+ }
+ nRead = MIN(filesize - pFile->iOffset, amt);
+ if( nRead>0 ){
+ rc = sqlite3OsRead(((AsyncFile *)id)->pBaseRead, obuf, nRead);
+ }
+ }
+
+ if( rc==SQLITE_OK ){
+ AsyncWrite *p;
+ i64 iOffset = pFile->iOffset; /* Current seek offset */
+
+ for(p=async.pQueueFirst; p; p = p->pNext){
+ if( p->pFile==pFile && p->op==ASYNC_WRITE ){
+ int iBeginIn = (p->iOffset - iOffset);
+ int iBeginOut = (iOffset - p->iOffset);
+ int nCopy;
+
+ if( iBeginIn<0 ) iBeginIn = 0;
+ if( iBeginOut<0 ) iBeginOut = 0;
+ nCopy = MIN(p->nByte-iBeginIn, amt-iBeginOut);
+
+ if( nCopy>0 ){
+ memcpy(&((char *)obuf)[iBeginOut], &p->zBuf[iBeginIn], nCopy);
+ }
+ }
+ }
+
+ pFile->iOffset += (i64)amt;
+ }
+
+asyncread_out:
+ pthread_mutex_unlock(&async.queueMutex);
+ return rc;
+}
+
+/*
+** Seek to the specified offset. This just adjusts the AsyncFile.iOffset
+** variable - calling seek() on the underlying file is defered until the
+** next read() or write() operation.
+*/
+static int asyncSeek(OsFile *id, i64 offset){
+ AsyncFile *pFile = (AsyncFile *)id;
+ pFile->iOffset = offset;
+ return SQLITE_OK;
+}
+
+/*
+** 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(OsFile *id, i64 *pSize){
+ int rc = SQLITE_OK;
+ i64 s = 0;
+ OsFile *pBase;
+
+ pthread_mutex_lock(&async.queueMutex);
+
+ /* Read the filesystem size from the base file. If pBaseRead 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 = ((AsyncFile *)id)->pBaseRead;
+ if( pBase ){
+ rc = sqlite3OsFileSize(pBase, &s);
+ }
+
+ if( rc==SQLITE_OK ){
+ AsyncWrite *p;
+ for(p=async.pQueueFirst; p; p = p->pNext){
+ if( p->pFile==(AsyncFile *)id ){
+ switch( p->op ){
+ case ASYNC_WRITE:
+ s = MAX(p->iOffset + (i64)(p->nByte), s);
+ break;
+ case ASYNC_TRUNCATE:
+ s = MIN(s, p->nByte);
+ break;
+ }
+ }
+ }
+ *pSize = s;
+ }
+ pthread_mutex_unlock(&async.queueMutex);
+ return rc;
+}
+
+/*
+** Return the operating system file handle. This is only used for debugging
+** at the moment anyway.
+*/
+static int asyncFileHandle(OsFile *id){
+ return sqlite3OsFileHandle(((AsyncFile *)id)->pBaseRead);
+}
+
+static int asyncLock(OsFile *id, int lockType){
+ return SQLITE_OK;
+}
+static int asyncUnlock(OsFile *id, int lockType){
+ return SQLITE_OK;
+}
+
+/*
+** This function is called when the pager layer first opens a database file
+** and is checking for a hot-journal.
+*/
+static int asyncCheckReservedLock(OsFile *id){
+ return SQLITE_OK;
+}
+
+/*
+** This is broken. But sqlite3OsLockState() is only used for testing anyway.
+*/
+static int asyncLockState(OsFile *id){
+ return SQLITE_OK;
+}
+
+/*
+** The following variables hold pointers to the original versions of
+** certain OS-layer interface routines - routines that this module
+** overrides.
+*/
+static int (*xOrigOpenReadWrite)(const char*, OsFile**, int*) = 0;
+static int (*xOrigOpenExclusive)(const char*, OsFile**, int) = 0;
+static int (*xOrigOpenReadOnly)(const char*, OsFile**) = 0;
+static int (*xOrigDelete)(const char*) = 0;
+static int (*xOrigFileExists)(const char*) = 0;
+static int (*xOrigSyncDirectory)(const char*) = 0;
+
+
+static int asyncOpenFile(
+ const char *zName,
+ OsFile **pFile,
+ OsFile *pBaseRead,
+ int openSecondFile
+){
+ int rc;
+ AsyncFile *p;
+ OsFile *pBaseWrite = 0;
+
+ static IoMethod iomethod = {
+ asyncClose,
+ asyncOpenDirectory,
+ asyncRead,
+ asyncWrite,
+ asyncSeek,
+ asyncTruncate,
+ asyncSync,
+ asyncSetFullSync,
+ asyncFileHandle,
+ asyncFileSize,
+ asyncLock,
+ asyncUnlock,
+ asyncLockState,
+ asyncCheckReservedLock
+ };
+
+ if( openSecondFile && SQLITE_ASYNC_TWO_FILEHANDLES ){
+ int dummy;
+ rc = xOrigOpenReadWrite(zName, &pBaseWrite, &dummy);
+ if( rc!=SQLITE_OK ){
+ goto error_out;
+ }
+ }
+
+ p = (AsyncFile *)sqlite3OsMalloc(sizeof(AsyncFile));
+ if( !p ){
+ rc = SQLITE_NOMEM;
+ goto error_out;
+ }
+ memset(p, 0, sizeof(AsyncFile));
+
+ p->pMethod = &iomethod;
+ p->pBaseRead = pBaseRead;
+ p->pBaseWrite = pBaseWrite;
+
+ *pFile = (OsFile *)p;
+ return SQLITE_OK;
+
+error_out:
+ assert(!p);
+ sqlite3OsClose(&pBaseRead);
+ sqlite3OsClose(&pBaseWrite);
+ *pFile = 0;
+ return rc;
+}
+
+/*
+** The async-IO backends implementation of the three functions used to open
+** a file (xOpenExclusive, xOpenReadWrite and xOpenReadOnly). Most of the
+** work is done in function asyncOpenFile() - see above.
+*/
+static int asyncOpenExclusive(const char *z, OsFile **ppFile, int delFlag){
+ int rc = asyncOpenFile(z, ppFile, 0, 0);
+ if( rc==SQLITE_OK ){
+ AsyncFile *pFile = (AsyncFile *)(*ppFile);
+ int nByte = strlen(z)+1;
+ i64 i = (i64)(delFlag);
+ rc = addNewAsyncWrite(pFile, ASYNC_OPENEXCLUSIVE, i, nByte, z);
+ if( rc!=SQLITE_OK ){
+ sqlite3OsFree(pFile);
+ *ppFile = 0;
+ }
+ }
+ return rc;
+}
+static int asyncOpenReadOnly(const char *z, OsFile **ppFile){
+ OsFile *pBase = 0;
+ int rc = xOrigOpenReadOnly(z, &pBase);
+ if( rc==SQLITE_OK ){
+ rc = asyncOpenFile(z, ppFile, pBase, 0);
+ }
+ return rc;
+}
+static int asyncOpenReadWrite(const char *z, OsFile **ppFile, int *pReadOnly){
+ OsFile *pBase = 0;
+ int rc = xOrigOpenReadWrite(z, &pBase, pReadOnly);
+ if( rc==SQLITE_OK ){
+ rc = asyncOpenFile(z, ppFile, pBase, (*pReadOnly ? 0 : 1));
+ }
+ return rc;
+}
+
+/*
+** Implementation of sqlite3OsDelete. Add an entry to the end of the
+** write-op queue to perform the delete.
+*/
+static int asyncDelete(const char *z){
+ return addNewAsyncWrite(0, ASYNC_DELETE, 0, strlen(z)+1, z);
+}
+
+/*
+** Implementation of sqlite3OsSyncDirectory. Add an entry to the end of the
+** write-op queue to perform the directory sync.
+*/
+static int asyncSyncDirectory(const char *z){
+ return addNewAsyncWrite(0, ASYNC_SYNCDIRECTORY, 0, strlen(z)+1, z);
+}
+
+/*
+** Implementation of sqlite3OsFileExists. Return true if file 'z' exists
+** in the file system.
+**
+** This method holds the mutex from start to finish.
+*/
+static int asyncFileExists(const char *z){
+ int ret;
+ AsyncWrite *p;
+
+ pthread_mutex_lock(&async.queueMutex);
+
+ /* See if the real file system contains the specified file. */
+ ret = xOrigFileExists(z);
+
+ for(p=async.pQueueFirst; p; p = p->pNext){
+ if( p->op==ASYNC_DELETE && 0==strcmp(p->zBuf, z) ){
+ ret = 0;
+ }else if( p->op==ASYNC_OPENEXCLUSIVE && 0==strcmp(p->zBuf, z) ){
+ ret = 1;
+ }
+ }
+
+ pthread_mutex_unlock(&async.queueMutex);
+ return ret;
+}
+
+/*
+** Call this routine to enable or disable the
+** asynchronous IO features implemented in this file.
+**
+** This routine is not even remotely threadsafe. Do not call
+** this routine while any SQLite database connections are open.
+*/
+static void asyncEnable(int enable){
+ if( enable && xOrigOpenReadWrite==0 ){
+ xOrigOpenReadWrite = sqlite3Os.xOpenReadWrite;
+ xOrigOpenReadOnly = sqlite3Os.xOpenReadOnly;
+ xOrigOpenExclusive = sqlite3Os.xOpenExclusive;
+ xOrigDelete = sqlite3Os.xDelete;
+ xOrigFileExists = sqlite3Os.xFileExists;
+ xOrigSyncDirectory = sqlite3Os.xSyncDirectory;
+
+ sqlite3Os.xOpenReadWrite = asyncOpenReadWrite;
+ sqlite3Os.xOpenReadOnly = asyncOpenReadOnly;
+ sqlite3Os.xOpenExclusive = asyncOpenExclusive;
+ sqlite3Os.xDelete = asyncDelete;
+ sqlite3Os.xFileExists = asyncFileExists;
+ sqlite3Os.xSyncDirectory = asyncSyncDirectory;
+ }
+ if( !enable && xOrigOpenReadWrite!=0 ){
+ sqlite3Os.xOpenReadWrite = xOrigOpenReadWrite;
+ sqlite3Os.xOpenReadOnly = xOrigOpenReadOnly;
+ sqlite3Os.xOpenExclusive = xOrigOpenExclusive;
+ sqlite3Os.xDelete = xOrigDelete;
+ sqlite3Os.xFileExists = xOrigFileExists;
+ sqlite3Os.xSyncDirectory = xOrigSyncDirectory;
+
+ xOrigOpenReadWrite = 0;
+ xOrigOpenReadOnly = 0;
+ xOrigOpenExclusive = 0;
+ xOrigDelete = 0;
+ xOrigFileExists = 0;
+ xOrigSyncDirectory = 0;
+ }
+}
+
+/*
+** 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 *NotUsed){
+ AsyncWrite *p = 0;
+ int rc = SQLITE_OK;
+
+ if( pthread_mutex_trylock(&async.writerMutex) ){
+ return 0;
+ }
+ while( async.writerHaltNow==0 ){
+ int holdingMutex;
+ OsFile *pBase = 0;
+
+ pthread_mutex_lock(&async.queueMutex);
+ holdingMutex = 1;
+ while( (p = async.pQueueFirst)==0 ){
+ pthread_cond_broadcast(&async.emptySignal);
+ if( async.writerHaltWhenIdle ){
+ pthread_mutex_unlock(&async.queueMutex);
+ break;
+ }else{
+ TRACE("IDLE\n", 0);
+ pthread_cond_wait(&async.queueSignal, &async.queueMutex);
+ TRACE("WAKEUP\n", 0);
+ }
+ }
+ if( p==0 ) break;
+ TRACE("PROCESSING %p\n", p);
+
+ /* 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( p->pFile ){
+ pBase = p->pFile->pBaseWrite;
+ if(
+ p->op==ASYNC_CLOSE ||
+ p->op==ASYNC_OPENEXCLUSIVE ||
+ (pBase && (p->op==ASYNC_SYNC || p->op==ASYNC_WRITE) )
+ ){
+ pthread_mutex_unlock(&async.queueMutex);
+ holdingMutex = 0;
+ }
+ if( !pBase ){
+ pBase = p->pFile->pBaseRead;
+ }
+ }
+
+ switch( p->op ){
+ case ASYNC_WRITE:
+ assert( pBase );
+ rc = sqlite3OsSeek(pBase, p->iOffset);
+ if( rc==SQLITE_OK ){
+ rc = sqlite3OsWrite(pBase, (const void *)(p->zBuf), p->nByte);
+ }
+ break;
+
+ case ASYNC_SYNC:
+ assert( pBase );
+ rc = sqlite3OsSync(pBase, p->nByte);
+ break;
+
+ case ASYNC_TRUNCATE:
+ assert( pBase );
+ rc = sqlite3OsTruncate(pBase, p->nByte);
+ break;
+
+ case ASYNC_CLOSE:
+ sqlite3OsClose(&p->pFile->pBaseRead);
+ sqlite3OsClose(&p->pFile->pBaseWrite);
+ sqlite3OsFree(p->pFile);
+ break;
+
+ case ASYNC_OPENDIRECTORY:
+ assert( pBase );
+ sqlite3OsOpenDirectory(pBase, p->zBuf);
+ break;
+
+ case ASYNC_SETFULLSYNC:
+ assert( pBase );
+ sqlite3OsSetFullSync(pBase, p->nByte);
+ break;
+
+ case ASYNC_DELETE:
+ rc = xOrigDelete(p->zBuf);
+ break;
+
+ case ASYNC_SYNCDIRECTORY:
+ rc = xOrigSyncDirectory(p->zBuf);
+ break;
+
+ case ASYNC_OPENEXCLUSIVE: {
+ AsyncFile *pFile = p->pFile;
+ int delFlag = ((p->iOffset)?1:0);
+ OsFile *pBase = 0;
+ rc = xOrigOpenExclusive(p->zBuf, &pBase, delFlag);
+ assert( holdingMutex==0 );
+ pthread_mutex_lock(&async.queueMutex);
+ holdingMutex = 1;
+ if( rc==SQLITE_OK ){
+ pFile->pBaseRead = pBase;
+ }
+ 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 ){
+ pthread_mutex_lock(&async.queueMutex);
+ holdingMutex = 1;
+ }
+ TRACE("UNLINK %p\n", p);
+ if( rc==SQLITE_OK ){
+ if( p==async.pQueueLast ){
+ async.pQueueLast = 0;
+ }
+ async.pQueueFirst = p->pNext;
+ }
+ assert( holdingMutex );
+
+ /* 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.
+ */
+ pthread_mutex_unlock(&async.queueMutex);
+ if( async.ioDelay>0 ){
+ sqlite3OsSleep(async.ioDelay);
+ }else{
+ sched_yield();
+ }
+ }
+ pthread_mutex_unlock(&async.writerMutex);
+ return 0;
+}
+
+/**************************************************************************
+** The remaining code defines a Tcl interface for testing the asynchronous
+** IO implementation in this file.
+**
+** To adapt the code to a non-TCL environment, delete or comment out
+** the code that follows.
+*/
+
+/*
+** sqlite3async_enable ?YES/NO?
+**
+** Enable or disable the asynchronous I/O backend. This command is
+** not thread-safe. Do not call it while any database connections
+** are open.
+*/
+static int testAsyncEnable(
+ void * clientData,
+ Tcl_Interp *interp,
+ int objc,
+ Tcl_Obj *CONST objv[]
+){
+ if( objc!=1 && objc!=2 ){
+ Tcl_WrongNumArgs(interp, 1, objv, "?YES/NO?");
+ return TCL_ERROR;
+ }
+ if( objc==1 ){
+ Tcl_SetObjResult(interp, Tcl_NewBooleanObj(xOrigOpenReadWrite!=0));
+ }else{
+ int en;
+ if( Tcl_GetBooleanFromObj(interp, objv[1], &en) ) return TCL_ERROR;
+ asyncEnable(en);
+ }
+ return TCL_OK;
+}
+
+/*
+** sqlite3async_halt "now"|"idle"|"never"
+**
+** Set the conditions at which the writer thread will halt.
+*/
+static int testAsyncHalt(
+ void * clientData,
+ Tcl_Interp *interp,
+ int objc,
+ Tcl_Obj *CONST objv[]
+){
+ const char *zCond;
+ if( objc!=2 ){
+ Tcl_WrongNumArgs(interp, 1, objv, "\"now\"|\"idle\"|\"never\"");
+ return TCL_ERROR;
+ }
+ zCond = Tcl_GetString(objv[1]);
+ if( strcmp(zCond, "now")==0 ){
+ async.writerHaltNow = 1;
+ pthread_cond_broadcast(&async.queueSignal);
+ }else if( strcmp(zCond, "idle")==0 ){
+ async.writerHaltWhenIdle = 1;
+ async.writerHaltNow = 0;
+ pthread_cond_broadcast(&async.queueSignal);
+ }else if( strcmp(zCond, "never")==0 ){
+ async.writerHaltWhenIdle = 0;
+ async.writerHaltNow = 0;
+ }else{
+ Tcl_AppendResult(interp,
+ "should be one of: \"now\", \"idle\", or \"never\"", (char*)0);
+ return TCL_ERROR;
+ }
+ return TCL_OK;
+}
+
+/*
+** sqlite3async_delay ?MS?
+**
+** Query or set the number of milliseconds of delay in the writer
+** thread after each write operation. The default is 0. By increasing
+** the memory delay we can simulate the effect of slow disk I/O.
+*/
+static int testAsyncDelay(
+ void * clientData,
+ Tcl_Interp *interp,
+ int objc,
+ Tcl_Obj *CONST objv[]
+){
+ if( objc!=1 && objc!=2 ){
+ Tcl_WrongNumArgs(interp, 1, objv, "?MS?");
+ return TCL_ERROR;
+ }
+ if( objc==1 ){
+ Tcl_SetObjResult(interp, Tcl_NewIntObj(async.ioDelay));
+ }else{
+ int ioDelay;
+ if( Tcl_GetIntFromObj(interp, objv[1], &ioDelay) ) return TCL_ERROR;
+ async.ioDelay = ioDelay;
+ }
+ return TCL_OK;
+}
+
+/*
+** sqlite3async_start
+**
+** Start a new writer thread.
+*/
+static int testAsyncStart(
+ void * clientData,
+ Tcl_Interp *interp,
+ int objc,
+ Tcl_Obj *CONST objv[]
+){
+ pthread_t x;
+ int rc;
+ rc = pthread_create(&x, 0, asyncWriterThread, 0);
+ if( rc ){
+ Tcl_AppendResult(interp, "failed to create the thread", 0);
+ return TCL_ERROR;
+ }
+ pthread_detach(x);
+ return TCL_OK;
+}
+
+/*
+** sqlite3async_wait
+**
+** Wait for the current writer thread to terminate.
+**
+** If the current writer thread is set to run forever then this
+** command would block forever. To prevent that, an error is returned.
+*/
+static int testAsyncWait(
+ void * clientData,
+ Tcl_Interp *interp,
+ int objc,
+ Tcl_Obj *CONST objv[]
+){
+ if( async.writerHaltNow==0 && async.writerHaltWhenIdle==0 ){
+ Tcl_AppendResult(interp, "would block forever", (char*)0);
+ return TCL_ERROR;
+ }
+ TRACE("WAIT\n",0);
+ pthread_cond_broadcast(&async.queueSignal);
+ pthread_mutex_lock(&async.writerMutex);
+ pthread_mutex_unlock(&async.writerMutex);
+ return TCL_OK;
+}
+
+
+#endif /* OS_UNIX and THREADSAFE and defined(SQLITE_ENABLE_REDEF_IO) */
+
+/*
+** This routine registers the custom TCL commands defined in this
+** module. This should be the only procedure visible from outside
+** of this module.
+*/
+int Sqlitetestasync_Init(Tcl_Interp *interp){
+#if OS_UNIX && THREADSAFE && defined(SQLITE_ENABLE_REDEF_IO)
+ Tcl_CreateObjCommand(interp,"sqlite3async_enable",testAsyncEnable,0,0);
+ Tcl_CreateObjCommand(interp,"sqlite3async_halt",testAsyncHalt,0,0);
+ Tcl_CreateObjCommand(interp,"sqlite3async_delay",testAsyncDelay,0,0);
+ Tcl_CreateObjCommand(interp,"sqlite3async_start",testAsyncStart,0,0);
+ Tcl_CreateObjCommand(interp,"sqlite3async_wait",testAsyncWait,0,0);
+#endif /* OS_UNIX and THREADSAFE and defined(SQLITE_ENABLE_REDEF_IO) */
+ return TCL_OK;
+}
projects / thirdparty / sqlite.git / commitdiff
