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On unix, embargo close() operations until all locks have cleared from the

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file.  Ticket #561. (CVS 1171)

FossilOrigin-Name: 1ebe5fc7b03a6b070a5d52ffedb95f0d519ab068
This commit is contained in:
drh
2004-01-12 00:39:05 +00:00
parent 7b40e60800
commit 31e95bcc5d
4 changed files with 228 additions and 67 deletions
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270
src/os.c
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@@ -164,6 +164,39 @@ static unsigned int elapse;
** structure. The fcntl() system call is only invoked to set a
** POSIX lock if the internal lock structure transitions between
** a locked and an unlocked state.
**
** 2004-Jan-11:
** More recent discoveries about POSIX advisory locks. (The more
** I discover, the more I realize the a POSIX advisory locks are
** an abomination.)
**
** If you close a file descriptor that points to a file that has locks,
** all locks on that file that are owned by the current process are
** released. To work around this problem, each OsFile structure contains
** a pointer to an openCnt structure. There is one openCnt structure
** per open inode, which means that multiple OsFiles can point to a single
** openCnt. When an attempt is made to close an OsFile, if there are
** other OsFiles open on the same inode that are holding locks, the call
** to close() the file descriptor is deferred until all of the locks clear.
** The openCnt structure keeps a list of file descriptors that need to
** be closed and that list is walked (and cleared) when the last lock
** clears.
**
** First, under Linux threads, because each thread has a separate
** process ID, lock operations in one thread do not override locks
** to the same file in other threads. Linux threads behave like
** separate processes in this respect. But, if you close a file
** descriptor in linux threads, all locks are cleared, even locks
** on other threads and even though the other threads have different
** process IDs. Linux threads is inconsistent in this respect.
** (I'm beginning to think that linux threads is an abomination too.)
** The consequence of this all is that the hash table for the lockInfo
** structure has to include the process id as part of its key because
** locks in different threads are treated as distinct. But the
** openCnt structure should not include the process id in its
** key because close() clears lock on all threads, not just the current
** thread. Were it not for this goofiness in linux threads, we could
** combine the lockInfo and openCnt structures into a single structure.
*/
/*
@@ -180,69 +213,147 @@ struct lockKey {
};
/*
** An instance of the following structure is allocated for each inode.
** An instance of the following structure is allocated for each open
** inode on each thread with a different process ID. (Threads have
** different process IDs on linux, but not on most other unixes.)
**
** A single inode can have multiple file descriptors, so each OsFile
** structure contains a pointer to an instance of this object and this
** object keeps a count of the number of OsFiles pointing to it.
*/
struct lockInfo {
struct lockKey key; /* The lookup key */
int cnt; /* 0: unlocked. -1: write lock. 1...: read lock. */
int cnt; /* 0: unlocked. -1: write lock. 1...: read lock. */
int nRef; /* Number of pointers to this structure */
};
/*
** An instance of the following structure serves as the key used
** to locate a particular openCnt structure given its inode. This
** is the same as the lockKey except that the process ID is omitted.
*/
struct openKey {
dev_t dev; /* Device number */
ino_t ino; /* Inode number */
};
/*
** An instance of the following structure is allocated for each open
** inode. This structure keeps track of the number of locks on that
** inode. If a close is attempted against an inode that is holding
** locks, the close is deferred until all locks clear by adding the
** file descriptor to be closed to the pending list.
*/
struct openCnt {
struct openKey key; /* The lookup key */
int nRef; /* Number of pointers to this structure */
int nLock; /* Number of outstanding locks */
int nPending; /* Number of pending close() operations */
int *aPending; /* Malloced space holding fd's awaiting a close() */
};
/*
** This hash table maps inodes (in the form of lockKey structures) into
** pointers to lockInfo structures.
** These hash table maps inodes and process IDs into lockInfo and openCnt
** structures. Access to these hash tables must be protected by a mutex.
*/
static Hash lockHash = { SQLITE_HASH_BINARY, 0, 0, 0, 0, 0 };
/*
** Given a file descriptor, locate a lockInfo structure that describes
** that file descriptor. Create a new one if necessary. NULL might
** be returned if malloc() fails.
*/
static struct lockInfo *findLockInfo(int fd){
int rc;
struct lockKey key;
struct stat statbuf;
struct lockInfo *pInfo;
rc = fstat(fd, &statbuf);
if( rc!=0 ) return 0;
memset(&key, 0, sizeof(key));
key.dev = statbuf.st_dev;
key.ino = statbuf.st_ino;
key.pid = getpid();
pInfo = (struct lockInfo*)sqliteHashFind(&lockHash, &key, sizeof(key));
if( pInfo==0 ){
struct lockInfo *pOld;
pInfo = sqliteMalloc( sizeof(*pInfo) );
if( pInfo==0 ) return 0;
pInfo->key = key;
pInfo->nRef = 1;
pInfo->cnt = 0;
pOld = sqliteHashInsert(&lockHash, &pInfo->key, sizeof(key), pInfo);
if( pOld!=0 ){
assert( pOld==pInfo );
sqliteFree(pInfo);
pInfo = 0;
}
}else{
pInfo->nRef++;
}
return pInfo;
}
static Hash openHash = { SQLITE_HASH_BINARY, 0, 0, 0, 0, 0 };
/*
** Release a lockInfo structure previously allocated by findLockInfo().
*/
static void releaseLockInfo(struct lockInfo *pInfo){
pInfo->nRef--;
if( pInfo->nRef==0 ){
sqliteHashInsert(&lockHash, &pInfo->key, sizeof(pInfo->key), 0);
sqliteFree(pInfo);
static void releaseLockInfo(struct lockInfo *pLock){
pLock->nRef--;
if( pLock->nRef==0 ){
sqliteHashInsert(&lockHash, &pLock->key, sizeof(pLock->key), 0);
sqliteFree(pLock);
}
}
/*
** Release a openCnt structure previously allocated by findLockInfo().
*/
static void releaseOpenCnt(struct openCnt *pOpen){
pOpen->nRef--;
if( pOpen->nRef==0 ){
sqliteHashInsert(&openHash, &pOpen->key, sizeof(pOpen->key), 0);
sqliteFree(pOpen->aPending);
sqliteFree(pOpen);
}
}
/*
** Given a file descriptor, locate lockInfo and openCnt structures that
** describes that file descriptor. Create a new ones if necessary. The
** return values might be unset if an error occurs.
**
** Return the number of errors.
*/
int findLockInfo(
int fd, /* The file descriptor used in the key */
struct lockInfo **ppLock, /* Return the lockInfo structure here */
struct openCnt **ppOpen /* Return the openCnt structure here */
){
int rc;
struct lockKey key1;
struct openKey key2;
struct stat statbuf;
struct lockInfo *pLock;
struct openCnt *pOpen;
rc = fstat(fd, &statbuf);
if( rc!=0 ) return 1;
memset(&key1, 0, sizeof(key1));
key1.dev = statbuf.st_dev;
key1.ino = statbuf.st_ino;
key1.pid = getpid();
memset(&key2, 0, sizeof(key2));
key2.dev = statbuf.st_dev;
key2.ino = statbuf.st_ino;
pLock = (struct lockInfo*)sqliteHashFind(&lockHash, &key1, sizeof(key1));
if( pLock==0 ){
struct lockInfo *pOld;
pLock = sqliteMallocRaw( sizeof(*pLock) );
if( pLock==0 ) return 1;
pLock->key = key1;
pLock->nRef = 1;
pLock->cnt = 0;
pOld = sqliteHashInsert(&lockHash, &pLock->key, sizeof(key1), pLock);
if( pOld!=0 ){
assert( pOld==pLock );
sqliteFree(pLock);
return 1;
}
}else{
pLock->nRef++;
}
*ppLock = pLock;
pOpen = (struct openCnt*)sqliteHashFind(&openHash, &key2, sizeof(key2));
if( pOpen==0 ){
struct openCnt *pOld;
pOpen = sqliteMallocRaw( sizeof(*pOpen) );
if( pOpen==0 ){
releaseLockInfo(pLock);
return 1;
}
pOpen->key = key2;
pOpen->nRef = 1;
pOpen->nLock = 0;
pOpen->nPending = 0;
pOpen->aPending = 0;
pOld = sqliteHashInsert(&openHash, &pOpen->key, sizeof(key2), pOpen);
if( pOld!=0 ){
assert( pOld==pOpen );
sqliteFree(pOpen);
releaseLockInfo(pLock);
return 1;
}
}else{
pOpen->nRef++;
}
*ppOpen = pOpen;
return 0;
}
#endif /** POSIX advisory lock work-around **/
/*
@@ -349,6 +460,7 @@ int sqliteOsOpenReadWrite(
int *pReadonly
){
#if OS_UNIX
int rc;
id->dirfd = -1;
id->fd = open(zFilename, O_RDWR|O_CREAT|O_LARGEFILE|O_BINARY, 0644);
if( id->fd<0 ){
@@ -361,9 +473,9 @@ int sqliteOsOpenReadWrite(
*pReadonly = 0;
}
sqliteOsEnterMutex();
id->pLock = findLockInfo(id->fd);
rc = findLockInfo(id->fd, &id->pLock, &id->pOpen);
sqliteOsLeaveMutex();
if( id->pLock==0 ){
if( rc ){
close(id->fd);
return SQLITE_NOMEM;
}
@@ -471,6 +583,7 @@ int sqliteOsOpenReadWrite(
*/
int sqliteOsOpenExclusive(const char *zFilename, OsFile *id, int delFlag){
#if OS_UNIX
int rc;
if( access(zFilename, 0)==0 ){
return SQLITE_CANTOPEN;
}
@@ -481,9 +594,9 @@ int sqliteOsOpenExclusive(const char *zFilename, OsFile *id, int delFlag){
return SQLITE_CANTOPEN;
}
sqliteOsEnterMutex();
id->pLock = findLockInfo(id->fd);
rc = findLockInfo(id->fd, &id->pLock, &id->pOpen);
sqliteOsLeaveMutex();
if( id->pLock==0 ){
if( rc ){
close(id->fd);
unlink(zFilename);
return SQLITE_NOMEM;
@@ -561,15 +674,16 @@ int sqliteOsOpenExclusive(const char *zFilename, OsFile *id, int delFlag){
*/
int sqliteOsOpenReadOnly(const char *zFilename, OsFile *id){
#if OS_UNIX
int rc;
id->dirfd = -1;
id->fd = open(zFilename, O_RDONLY|O_LARGEFILE|O_BINARY);
if( id->fd<0 ){
return SQLITE_CANTOPEN;
}
sqliteOsEnterMutex();
id->pLock = findLockInfo(id->fd);
rc = findLockInfo(id->fd, &id->pLock, &id->pOpen);
sqliteOsLeaveMutex();
if( id->pLock==0 ){
if( rc ){
close(id->fd);
return SQLITE_NOMEM;
}
@@ -763,15 +877,36 @@ int sqliteOsTempFileName(char *zBuf){
}
/*
** Close a file
** Close a file.
*/
int sqliteOsClose(OsFile *id){
#if OS_UNIX
close(id->fd);
sqliteOsUnlock(id);
if( id->dirfd>=0 ) close(id->dirfd);
id->dirfd = -1;
sqliteOsEnterMutex();
if( id->pOpen->nLock ){
/* If there are outstanding locks, do not actually close the file just
** yet because that would clear those locks. Instead, add the file
** descriptor to pOpen->aPending. It will be automatically closed when
** the last lock is cleared.
*/
int *aNew;
struct openCnt *pOpen = id->pOpen;
pOpen->nPending++;
aNew = sqliteRealloc( pOpen->aPending, pOpen->nPending*sizeof(int) );
if( aNew==0 ){
/* If a malloc fails, just leak the file descriptor */
}else{
pOpen->aPending = aNew;
pOpen->aPending[pOpen->nPending-1] = id->fd;
}
}else{
/* There are no outstanding locks so we can close the file immediately */
close(id->fd);
}
releaseLockInfo(id->pLock);
releaseOpenCnt(id->pOpen);
sqliteOsLeaveMutex();
TRACE2("CLOSE %-3d\n", id->fd);
OpenCounter(-1);
@@ -1159,6 +1294,7 @@ int sqliteOsReadLock(OsFile *id){
if( !id->locked ){
id->pLock->cnt++;
id->locked = 1;
id->pOpen->nLock++;
}
rc = SQLITE_OK;
}else if( id->locked || id->pLock->cnt==0 ){
@@ -1172,8 +1308,11 @@ int sqliteOsReadLock(OsFile *id){
rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
}else{
rc = SQLITE_OK;
if( !id->locked ){
id->pOpen->nLock++;
id->locked = 1;
}
id->pLock->cnt = 1;
id->locked = 1;
}
}else{
rc = SQLITE_BUSY;
@@ -1276,8 +1415,11 @@ int sqliteOsWriteLock(OsFile *id){
rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
}else{
rc = SQLITE_OK;
if( !id->locked ){
id->pOpen->nLock++;
id->locked = 1;
}
id->pLock->cnt = -1;
id->locked = 1;
}
}else{
rc = SQLITE_BUSY;
@@ -1391,6 +1533,24 @@ int sqliteOsUnlock(OsFile *id){
id->pLock->cnt = 0;
}
}
if( rc==SQLITE_OK ){
/* Decrement the count of locks against this same file. When the
** count reaches zero, close any other file descriptors whose close
** was deferred because of outstanding locks.
*/
struct openCnt *pOpen = id->pOpen;
pOpen->nLock--;
assert( pOpen->nLock>=0 );
if( pOpen->nLock==0 && pOpen->nPending>0 ){
int i;
for(i=0; i<pOpen->nPending; i++){
close(pOpen->aPending[i]);
}
sqliteFree(pOpen->aPending);
pOpen->nPending = 0;
pOpen->aPending = 0;
}
}
sqliteOsLeaveMutex();
id->locked = 0;
return rc;