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-rw-r--r--src/os_win.c199
1 files changed, 168 insertions, 31 deletions
diff --git a/src/os_win.c b/src/os_win.c
index 245a86045..9bfcfe1c8 100644
--- a/src/os_win.c
+++ b/src/os_win.c
@@ -2099,6 +2099,17 @@ static int winIoerrRetry = SQLITE_WIN32_IOERR_RETRY;
static int winIoerrRetryDelay = SQLITE_WIN32_IOERR_RETRY_DELAY;
/*
+** The "winIsLockingError" macro is used to determine if a particular I/O
+** error code is due to file locking. It must accept the error code DWORD
+** as its only argument and should return non-zero if the error code is due
+** to file locking.
+*/
+#if !defined(winIsLockingError)
+#define winIsLockingError(a) (((a)==ERROR_LOCK_VIOLATION) || \
+ ((a)==ERROR_IO_PENDING))
+#endif
+
+/*
** The "winIoerrCanRetry1" macro is used to determine if a particular I/O
** error code obtained via GetLastError() is eligible to be retried. It
** must accept the error code DWORD as its only argument and should return
@@ -3673,6 +3684,9 @@ struct winShmNode {
int szRegion; /* Size of shared-memory regions */
int nRegion; /* Size of array apRegion */
+ u8 isReadonly; /* True if read-only */
+ u8 isUnlocked; /* True if no DMS lock held */
+
struct ShmRegion {
HANDLE hMap; /* File handle from CreateFileMapping */
void *pMap;
@@ -3821,6 +3835,116 @@ static void winShmPurge(sqlite3_vfs *pVfs, int deleteFlag){
}
/*
+** Query the status of the DMS lock for the specified file. Returns
+** SQLITE_OK upon success. Upon success, the integer pointed to by
+** the pLockType argument will be set to the lock type held by the
+** other process, as follows:
+**
+** WINSHM_UNLCK -- No locks are held on the DMS.
+** WINSHM_RDLCK -- A SHARED lock is held on the DMS.
+** WINSHM_WRLCK -- An EXCLUSIVE lock is held on the DMS.
+*/
+static int winGetShmDmsLockType(
+ winFile *pFile, /* File handle object */
+ int *pLockType /* WINSHM_UNLCK, WINSHM_RDLCK, or WINSHM_WRLCK */
+){
+#if !SQLITE_OS_WINCE && !defined(SQLITE_WIN32_NO_OVERLAPPED)
+ OVERLAPPED overlapped; /* The offset for ReadFile/WriteFile. */
+#endif
+ LPVOID pOverlapped = 0;
+ sqlite3_int64 offset = WIN_SHM_DMS;
+ BYTE notUsed1 = 0;
+ DWORD notUsed2 = 0;
+
+#if SQLITE_OS_WINCE || defined(SQLITE_WIN32_NO_OVERLAPPED)
+ if( winSeekFile(pFile, offset) ){
+ return SQLITE_IOERR_SEEK;
+ }
+#else
+ memset(&overlapped, 0, sizeof(OVERLAPPED));
+ overlapped.Offset = (LONG)(offset & 0xffffffff);
+ overlapped.OffsetHigh = (LONG)((offset>>32) & 0x7fffffff);
+ pOverlapped = &overlapped;
+#endif
+ if( !osWriteFile(pFile->h, &notUsed1, 1, &notUsed2, pOverlapped) ){
+ if( !osReadFile(pFile->h, &notUsed1, 1, &notUsed2, pOverlapped) ){
+ if( winIsLockingError(osGetLastError()) ){
+ *pLockType = WINSHM_WRLCK;
+ }else{
+ return SQLITE_IOERR_READ;
+ }
+ }else{
+ if( winIsLockingError(osGetLastError()) ){
+ *pLockType = WINSHM_RDLCK;
+ }else{
+ return SQLITE_IOERR_WRITE;
+ }
+ }
+ }else{
+ *pLockType = WINSHM_UNLCK;
+ }
+ return SQLITE_OK;
+}
+
+/*
+** The DMS lock has not yet been taken on shm file pShmNode. Attempt to
+** take it now. Return SQLITE_OK if successful, or an SQLite error
+** code otherwise.
+**
+** If the DMS cannot be locked because this is a readonly_shm=1
+** connection and no other process already holds a lock, return
+** SQLITE_READONLY_CANTINIT and set pShmNode->isUnlocked=1.
+*/
+static int winLockSharedMemory(winFile *pDbFd, winShmNode *pShmNode){
+ int lockType;
+ int rc = SQLITE_OK;
+
+ /* Use ReadFile/WriteFile to determine the locks other processes are
+ ** holding on the DMS byte. If it indicates that another process is
+ ** holding a SHARED lock, then this process may also take a SHARED
+ ** lock and proceed with opening the *-shm file.
+ **
+ ** Or, if no other process is holding any lock, then this process
+ ** is the first to open it. In this case take an EXCLUSIVE lock on the
+ ** DMS byte and truncate the *-shm file to zero bytes in size. Then
+ ** downgrade to a SHARED lock on the DMS byte.
+ **
+ ** If another process is holding an EXCLUSIVE lock on the DMS byte,
+ ** return SQLITE_BUSY to the caller (it will try again). An earlier
+ ** version of this code attempted the SHARED lock at this point. But
+ ** this introduced a subtle race condition: if the process holding
+ ** EXCLUSIVE failed just before truncating the *-shm file, then this
+ ** process might open and use the *-shm file without truncating it.
+ ** And if the *-shm file has been corrupted by a power failure or
+ ** system crash, the database itself may also become corrupt. */
+ if( winGetShmDmsLockType(&pShmNode->hFile, &lockType)!=SQLITE_OK ){
+ rc = SQLITE_IOERR_LOCK;
+ }else if( lockType==WINSHM_UNLCK ){
+ if( pShmNode->isReadonly ){
+ pShmNode->isUnlocked = 1;
+ rc = SQLITE_READONLY_CANTINIT;
+ }else{
+ winShmSystemLock(pShmNode, WINSHM_UNLCK, WIN_SHM_DMS, 1);
+ rc = winShmSystemLock(pShmNode, WINSHM_WRLCK, WIN_SHM_DMS, 1);
+ if( rc==SQLITE_OK && winTruncate((sqlite3_file*)&pShmNode->hFile, 0) ){
+ rc = winLogError(SQLITE_IOERR_SHMOPEN, osGetLastError(),
+ "winLockSharedMemory", pShmNode->zFilename);
+ }
+ }
+ }else if( lockType==WINSHM_WRLCK ){
+ rc = SQLITE_BUSY;
+ }
+
+ if( rc==SQLITE_OK ){
+ assert( lockType==WINSHM_UNLCK || lockType==WINSHM_RDLCK );
+ winShmSystemLock(pShmNode, WINSHM_UNLCK, WIN_SHM_DMS, 1);
+ rc = winShmSystemLock(pShmNode, WINSHM_RDLCK, WIN_SHM_DMS, 1);
+ }
+
+ return rc;
+}
+
+/*
** Open the shared-memory area associated with database file pDbFd.
**
** When opening a new shared-memory file, if no other instances of that
@@ -3828,11 +3952,12 @@ static void winShmPurge(sqlite3_vfs *pVfs, int deleteFlag){
** the file must be truncated to zero length or have its header cleared.
*/
static int winOpenSharedMemory(winFile *pDbFd){
- struct winShm *p; /* The connection to be opened */
- struct winShmNode *pShmNode = 0; /* The underlying mmapped file */
- int rc; /* Result code */
- struct winShmNode *pNew; /* Newly allocated winShmNode */
- int nName; /* Size of zName in bytes */
+ struct winShm *p; /* The connection to be opened */
+ winShmNode *pShmNode = 0; /* The underlying mmapped file */
+ int rc = SQLITE_OK; /* Result code */
+ int rc2 = SQLITE_ERROR; /* winOpen result code */
+ winShmNode *pNew; /* Newly allocated winShmNode */
+ int nName; /* Size of zName in bytes */
assert( pDbFd->pShm==0 ); /* Not previously opened */
@@ -3878,30 +4003,29 @@ static int winOpenSharedMemory(winFile *pDbFd){
}
}
- rc = winOpen(pDbFd->pVfs,
- pShmNode->zFilename, /* Name of the file (UTF-8) */
- (sqlite3_file*)&pShmNode->hFile, /* File handle here */
- SQLITE_OPEN_WAL | SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE,
- 0);
- if( SQLITE_OK!=rc ){
- goto shm_open_err;
+ if( 0==sqlite3_uri_boolean(pDbFd->zPath, "readonly_shm", 0) ){
+ rc2 = winOpen(pDbFd->pVfs,
+ pShmNode->zFilename,
+ (sqlite3_file*)&pShmNode->hFile,
+ SQLITE_OPEN_WAL|SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE,
+ 0);
}
-
- /* Check to see if another process is holding the dead-man switch.
- ** If not, truncate the file to zero length.
- */
- if( winShmSystemLock(pShmNode, WINSHM_WRLCK, WIN_SHM_DMS, 1)==SQLITE_OK ){
- rc = winTruncate((sqlite3_file *)&pShmNode->hFile, 0);
- if( rc!=SQLITE_OK ){
- rc = winLogError(SQLITE_IOERR_SHMOPEN, osGetLastError(),
- "winOpenShm", pDbFd->zPath);
+ if( rc2!=SQLITE_OK ){
+ rc2 = winOpen(pDbFd->pVfs,
+ pShmNode->zFilename,
+ (sqlite3_file*)&pShmNode->hFile,
+ SQLITE_OPEN_WAL|SQLITE_OPEN_READONLY|SQLITE_OPEN_CREATE,
+ 0);
+ if( rc2!=SQLITE_OK ){
+ rc = winLogError(SQLITE_CANTOPEN_BKPT, osGetLastError(),
+ "winOpenShm", pShmNode->zFilename);
+ goto shm_open_err;
}
+ pShmNode->isReadonly = 1;
}
- if( rc==SQLITE_OK ){
- winShmSystemLock(pShmNode, WINSHM_UNLCK, WIN_SHM_DMS, 1);
- rc = winShmSystemLock(pShmNode, WINSHM_RDLCK, WIN_SHM_DMS, 1);
- }
- if( rc ) goto shm_open_err;
+
+ rc = winLockSharedMemory(pDbFd, pShmNode);
+ if( rc!=SQLITE_OK && rc!=SQLITE_READONLY_CANTINIT ) goto shm_open_err;
}
/* Make the new connection a child of the winShmNode */
@@ -4128,6 +4252,8 @@ static int winShmMap(
winFile *pDbFd = (winFile*)fd;
winShm *pShm = pDbFd->pShm;
winShmNode *pShmNode;
+ DWORD protect = PAGE_READWRITE;
+ DWORD flags = FILE_MAP_WRITE | FILE_MAP_READ;
int rc = SQLITE_OK;
if( !pShm ){
@@ -4138,6 +4264,11 @@ static int winShmMap(
pShmNode = pShm->pShmNode;
sqlite3_mutex_enter(pShmNode->mutex);
+ if( pShmNode->isUnlocked ){
+ rc = winLockSharedMemory(pDbFd, pShmNode);
+ if( rc!=SQLITE_OK ) goto shmpage_out;
+ pShmNode->isUnlocked = 0;
+ }
assert( szRegion==pShmNode->szRegion || pShmNode->nRegion==0 );
if( pShmNode->nRegion<=iRegion ){
@@ -4184,21 +4315,26 @@ static int winShmMap(
}
pShmNode->aRegion = apNew;
+ if( pShmNode->isReadonly ){
+ protect = PAGE_READONLY;
+ flags = FILE_MAP_READ;
+ }
+
while( pShmNode->nRegion<=iRegion ){
HANDLE hMap = NULL; /* file-mapping handle */
void *pMap = 0; /* Mapped memory region */
#if SQLITE_OS_WINRT
hMap = osCreateFileMappingFromApp(pShmNode->hFile.h,
- NULL, PAGE_READWRITE, nByte, NULL
+ NULL, protect, nByte, NULL
);
#elif defined(SQLITE_WIN32_HAS_WIDE)
hMap = osCreateFileMappingW(pShmNode->hFile.h,
- NULL, PAGE_READWRITE, 0, nByte, NULL
+ NULL, protect, 0, nByte, NULL
);
#elif defined(SQLITE_WIN32_HAS_ANSI) && SQLITE_WIN32_CREATEFILEMAPPINGA
hMap = osCreateFileMappingA(pShmNode->hFile.h,
- NULL, PAGE_READWRITE, 0, nByte, NULL
+ NULL, protect, 0, nByte, NULL
);
#endif
OSTRACE(("SHM-MAP-CREATE pid=%lu, region=%d, size=%d, rc=%s\n",
@@ -4208,11 +4344,11 @@ static int winShmMap(
int iOffset = pShmNode->nRegion*szRegion;
int iOffsetShift = iOffset % winSysInfo.dwAllocationGranularity;
#if SQLITE_OS_WINRT
- pMap = osMapViewOfFileFromApp(hMap, FILE_MAP_WRITE | FILE_MAP_READ,
+ pMap = osMapViewOfFileFromApp(hMap, flags,
iOffset - iOffsetShift, szRegion + iOffsetShift
);
#else
- pMap = osMapViewOfFile(hMap, FILE_MAP_WRITE | FILE_MAP_READ,
+ pMap = osMapViewOfFile(hMap, flags,
0, iOffset - iOffsetShift, szRegion + iOffsetShift
);
#endif
@@ -4243,6 +4379,7 @@ shmpage_out:
}else{
*pp = 0;
}
+ if( pShmNode->isReadonly && rc==SQLITE_OK ) rc = SQLITE_READONLY;
sqlite3_mutex_leave(pShmNode->mutex);
return rc;
}
generated by cgit v1.2.3 (git 2.25.1) at 2025-07-19 13:11:49 +0000