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-rw-r--r--src/os_unix.c28
-rw-r--r--src/sqlite.h.in8
-rw-r--r--src/wal.c17
3 files changed, 36 insertions, 17 deletions
diff --git a/src/os_unix.c b/src/os_unix.c
index 927b9e1c5..16cb935de 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -248,6 +248,7 @@ static pid_t randomnessPid = 0;
#define UNIXFILE_URI 0x40 /* Filename might have query parameters */
#define UNIXFILE_NOLOCK 0x80 /* Do no file locking */
#define UNIXFILE_WARNED 0x0100 /* verifyDbFile() warnings issued */
+#define UNIXFILE_BLOCK 0x0200 /* Next SHM lock might block */
/*
** Include code that is common to all os_*.c files
@@ -4090,15 +4091,17 @@ struct unixShm {
** otherwise.
*/
static int unixShmSystemLock(
- unixShmNode *pShmNode, /* Apply locks to this open shared-memory segment */
+ unixFile *pFile, /* Open connection to the WAL file */
int lockType, /* F_UNLCK, F_RDLCK, or F_WRLCK */
int ofst, /* First byte of the locking range */
int n /* Number of bytes to lock */
){
- struct flock f; /* The posix advisory locking structure */
- int rc = SQLITE_OK; /* Result code form fcntl() */
+ unixShmNode *pShmNode; /* Apply locks to this open shared-memory segment */
+ struct flock f; /* The posix advisory locking structure */
+ int rc = SQLITE_OK; /* Result code form fcntl() */
/* Access to the unixShmNode object is serialized by the caller */
+ pShmNode = pFile->pInode->pShmNode;
assert( sqlite3_mutex_held(pShmNode->mutex) || pShmNode->nRef==0 );
/* Shared locks never span more than one byte */
@@ -4108,6 +4111,7 @@ static int unixShmSystemLock(
assert( n>=1 && n<SQLITE_SHM_NLOCK );
if( pShmNode->h>=0 ){
+ int lkType;
/* Initialize the locking parameters */
memset(&f, 0, sizeof(f));
f.l_type = lockType;
@@ -4115,8 +4119,10 @@ static int unixShmSystemLock(
f.l_start = ofst;
f.l_len = n;
- rc = osFcntl(pShmNode->h, F_SETLK, &f);
+ lkType = (pFile->ctrlFlags & UNIXFILE_BLOCK)!=0 ? F_SETLKW : F_SETLK;
+ rc = osFcntl(pShmNode->h, lkType, &f);
rc = (rc!=(-1)) ? SQLITE_OK : SQLITE_BUSY;
+ pFile->ctrlFlags &= ~UNIXFILE_BLOCK;
}
/* Update the global lock state and do debug tracing */
@@ -4326,13 +4332,13 @@ static int unixOpenSharedMemory(unixFile *pDbFd){
** If not, truncate the file to zero length.
*/
rc = SQLITE_OK;
- if( unixShmSystemLock(pShmNode, F_WRLCK, UNIX_SHM_DMS, 1)==SQLITE_OK ){
+ if( unixShmSystemLock(pDbFd, F_WRLCK, UNIX_SHM_DMS, 1)==SQLITE_OK ){
if( robust_ftruncate(pShmNode->h, 0) ){
rc = unixLogError(SQLITE_IOERR_SHMOPEN, "ftruncate", zShmFilename);
}
}
if( rc==SQLITE_OK ){
- rc = unixShmSystemLock(pShmNode, F_RDLCK, UNIX_SHM_DMS, 1);
+ rc = unixShmSystemLock(pDbFd, F_RDLCK, UNIX_SHM_DMS, 1);
}
if( rc ) goto shm_open_err;
}
@@ -4564,7 +4570,7 @@ static int unixShmLock(
/* Unlock the system-level locks */
if( (mask & allMask)==0 ){
- rc = unixShmSystemLock(pShmNode, F_UNLCK, ofst+UNIX_SHM_BASE, n);
+ rc = unixShmSystemLock(pDbFd, F_UNLCK, ofst+UNIX_SHM_BASE, n);
}else{
rc = SQLITE_OK;
}
@@ -4592,7 +4598,7 @@ static int unixShmLock(
/* Get shared locks at the system level, if necessary */
if( rc==SQLITE_OK ){
if( (allShared & mask)==0 ){
- rc = unixShmSystemLock(pShmNode, F_RDLCK, ofst+UNIX_SHM_BASE, n);
+ rc = unixShmSystemLock(pDbFd, F_RDLCK, ofst+UNIX_SHM_BASE, n);
}else{
rc = SQLITE_OK;
}
@@ -4617,7 +4623,7 @@ static int unixShmLock(
** also mark the local connection as being locked.
*/
if( rc==SQLITE_OK ){
- rc = unixShmSystemLock(pShmNode, F_WRLCK, ofst+UNIX_SHM_BASE, n);
+ rc = unixShmSystemLock(pDbFd, F_WRLCK, ofst+UNIX_SHM_BASE, n);
if( rc==SQLITE_OK ){
assert( (p->sharedMask & mask)==0 );
p->exclMask |= mask;
@@ -7222,6 +7228,10 @@ static int proxyTransformUnixFile(unixFile *pFile, const char *path) {
*/
static int proxyFileControl(sqlite3_file *id, int op, void *pArg){
switch( op ){
+ case SQLITE_FCNTL_WAL_BLOCK: {
+ id->ctrlFlags |= UNIXFILE_BLOCK;
+ return SQLITE_OK;
+ }
case SQLITE_FCNTL_GET_LOCKPROXYFILE: {
unixFile *pFile = (unixFile*)id;
if( pFile->pMethod == &proxyIoMethods ){
diff --git a/src/sqlite.h.in b/src/sqlite.h.in
index 06e0f7eb9..f0f6f5ddc 100644
--- a/src/sqlite.h.in
+++ b/src/sqlite.h.in
@@ -945,6 +945,13 @@ struct sqlite3_io_methods {
** pointed to by the pArg argument. This capability is used during testing
** and only needs to be supported when SQLITE_TEST is defined.
**
+** <li>[[SQLITE_FCNTL_WAL_BLOCK]]
+** The [SQLITE_FCNTL_WAL_BLOCK] is a single to the VFS layer that it might
+** be advantageous to block on the next WAL lock if the lock is not immediately
+** available. The WAL subsystem issues this ioctl() during some rare
+** circumstances in order to fix a problem with priority inversion.
+** Applications should <em>not</em> use this file-control.
+**
** </ul>
*/
#define SQLITE_FCNTL_LOCKSTATE 1
@@ -969,6 +976,7 @@ struct sqlite3_io_methods {
#define SQLITE_FCNTL_SYNC 21
#define SQLITE_FCNTL_COMMIT_PHASETWO 22
#define SQLITE_FCNTL_WIN32_SET_HANDLE 23
+#define SQLITE_FCNTL_WAL_BLOCK 24
/* deprecated names */
#define SQLITE_GET_LOCKPROXYFILE SQLITE_FCNTL_GET_LOCKPROXYFILE
diff --git a/src/wal.c b/src/wal.c
index 71f4a3d45..558adbcad 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -788,9 +788,10 @@ static void walUnlockShared(Wal *pWal, int lockIdx){
SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED);
WALTRACE(("WAL%p: release SHARED-%s\n", pWal, walLockName(lockIdx)));
}
-static int walLockExclusive(Wal *pWal, int lockIdx, int n){
+static int walLockExclusive(Wal *pWal, int lockIdx, int n, int fBlock){
int rc;
if( pWal->exclusiveMode ) return SQLITE_OK;
+ if( fBlock ) sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_WAL_BLOCK, 0);
rc = sqlite3OsShmLock(pWal->pDbFd, lockIdx, n,
SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE);
WALTRACE(("WAL%p: acquire EXCLUSIVE-%s cnt=%d %s\n", pWal,
@@ -1076,7 +1077,7 @@ static int walIndexRecover(Wal *pWal){
assert( pWal->writeLock );
iLock = WAL_ALL_BUT_WRITE + pWal->ckptLock;
nLock = SQLITE_SHM_NLOCK - iLock;
- rc = walLockExclusive(pWal, iLock, nLock);
+ rc = walLockExclusive(pWal, iLock, nLock, 0);
if( rc ){
return rc;
}
@@ -1610,7 +1611,7 @@ static int walBusyLock(
){
int rc;
do {
- rc = walLockExclusive(pWal, lockIdx, n);
+ rc = walLockExclusive(pWal, lockIdx, n, 0);
}while( xBusy && rc==SQLITE_BUSY && xBusy(pBusyArg) );
return rc;
}
@@ -2043,7 +2044,7 @@ static int walIndexReadHdr(Wal *pWal, int *pChanged){
walUnlockShared(pWal, WAL_WRITE_LOCK);
rc = SQLITE_READONLY_RECOVERY;
}
- }else if( SQLITE_OK==(rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1)) ){
+ }else if( SQLITE_OK==(rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1, 1)) ){
pWal->writeLock = 1;
if( SQLITE_OK==(rc = walIndexPage(pWal, 0, &page0)) ){
badHdr = walIndexTryHdr(pWal, pChanged);
@@ -2249,7 +2250,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
&& (mxReadMark<pWal->hdr.mxFrame || mxI==0)
){
for(i=1; i<WAL_NREADER; i++){
- rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
+ rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1, 0);
if( rc==SQLITE_OK ){
mxReadMark = pInfo->aReadMark[i] = pWal->hdr.mxFrame;
mxI = i;
@@ -2505,7 +2506,7 @@ int sqlite3WalBeginWriteTransaction(Wal *pWal){
/* Only one writer allowed at a time. Get the write lock. Return
** SQLITE_BUSY if unable.
*/
- rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1);
+ rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1, 0);
if( rc ){
return rc;
}
@@ -2650,7 +2651,7 @@ static int walRestartLog(Wal *pWal){
if( pInfo->nBackfill>0 ){
u32 salt1;
sqlite3_randomness(4, &salt1);
- rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
+ rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1, 0);
if( rc==SQLITE_OK ){
/* If all readers are using WAL_READ_LOCK(0) (in other words if no
** readers are currently using the WAL), then the transactions
@@ -2975,7 +2976,7 @@ int sqlite3WalCheckpoint(
/* IMPLEMENTATION-OF: R-62028-47212 All calls obtain an exclusive
** "checkpoint" lock on the database file. */
- rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
+ rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1, 0);
if( rc ){
/* EVIDENCE-OF: R-10421-19736 If any other process is running a
** checkpoint operation at the same time, the lock cannot be obtained and
generated by cgit v1.2.3 (git 2.25.1) at 2025-07-21 04:41:30 +0000