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Fix the locking protocol. (CVS 280)

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FossilOrigin-Name: 484b82d8a1c84f3d9725a509de93276b9fa9b294
This commit is contained in:
drh
2001-10-09 04:19:46 +00:00
parent f57b339988
commit ad75e9874b
13 changed files with 413 additions and 134 deletions
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220
src/os.c
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@@ -37,6 +37,73 @@
# include <winbase.h>
#endif
#if OS_UNIX
/*
** An instance of the following structure serves as the key used
** to locate a particular lockInfo structure given its inode.
*/
struct inodeKey {
dev_t dev; /* Device number */
ino_t ino; /* Inode number */
};
/*
** An instance of the following structure is allocated for each inode.
** A single inode can have multiple file descriptors, so each OsFile structure
** contains a pointer to an instance of this object.
*/
struct lockInfo {
struct inodeKey key; /* The lookup key */
int cnt; /* 0: unlocked. -1: write lock. >=1: read lock */
int nRef; /* Number of pointers to this structure */
};
/*
** This hash table maps inodes (in the form of inodeKey structures) into
** pointers to lockInfo structures.
*/
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.
*/
static struct lockInfo *findLockInfo(int fd){
int rc;
struct inodeKey key;
struct stat statbuf;
struct lockInfo *pInfo;
rc = fstat(fd, &statbuf);
if( rc!=0 ) return 0;
key.dev = statbuf.st_dev;
key.ino = statbuf.st_ino;
pInfo = (struct lockInfo*)sqliteHashFind(&lockHash, &key, sizeof(key));
if( pInfo==0 ){
pInfo = sqliteMalloc( sizeof(*pInfo) );
pInfo->key = key;
pInfo->nRef = 1;
pInfo->cnt = 0;
sqliteHashInsert(&lockHash, &pInfo->key, sizeof(key), pInfo);
}else{
pInfo->nRef++;
}
return pInfo;
}
/*
** 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);
}
}
#endif
/*
** Delete the named file
*/
@@ -95,17 +162,25 @@ int sqliteOsOpenReadWrite(
int *pReadonly
){
#if OS_UNIX
int fd = open(zFilename, O_RDWR|O_CREAT, 0644);
if( fd<0 ){
fd = open(zFilename, O_RDONLY);
if( fd<0 ){
OsFile s;
s.fd = open(zFilename, O_RDWR|O_CREAT, 0644);
if( s.fd<0 ){
s.fd = open(zFilename, O_RDONLY);
if( s.fd<0 ){
return SQLITE_CANTOPEN;
}
*pReadonly = 1;
}else{
*pReadonly = 0;
}
*pResult = fd;
sqliteOsEnterMutex();
s.pLock = findLockInfo(s.fd);
sqliteOsLeaveMutex();
if( s.pLock==0 ){
close(s.fd);
return SQLITE_NOMEM;
}
*pResult = s;
return SQLITE_OK;
#endif
#if OS_WIN
@@ -152,18 +227,25 @@ int sqliteOsOpenReadWrite(
*/
int sqliteOsOpenExclusive(const char *zFilename, OsFile *pResult){
#if OS_UNIX
int fd;
OsFile s;
if( access(zFilename, 0)==0 ){
return SQLITE_CANTOPEN;
}
#ifndef O_NOFOLLOW
# define O_NOFOLLOW 0
#endif
fd = open(zFilename, O_RDWR|O_CREAT|O_EXCL|O_NOFOLLOW, 0600);
if( fd<0 ){
s.fd = open(zFilename, O_RDWR|O_CREAT|O_EXCL|O_NOFOLLOW, 0600);
if( s.fd<0 ){
return SQLITE_CANTOPEN;
}
*pResult = fd;
sqliteOsEnterMutex();
s.pLock = findLockInfo(s.fd);
sqliteOsLeaveMutex();
if( s.pLock==0 ){
close(s.fd);
return SQLITE_NOMEM;
}
*pResult = s;
return SQLITE_OK;
#endif
#if OS_WIN
@@ -192,11 +274,19 @@ int sqliteOsOpenExclusive(const char *zFilename, OsFile *pResult){
*/
int sqliteOsOpenReadOnly(const char *zFilename, OsFile *pResult){
#if OS_UNIX
int fd = open(zFilename, O_RDONLY);
if( fd<0 ){
OsFile s;
s.fd = open(zFilename, O_RDONLY);
if( s.fd<0 ){
return SQLITE_CANTOPEN;
}
*pResult = fd;
sqliteOsEnterMutex();
s.pLock = findLockInfo(s.fd);
sqliteOsLeaveMutex();
if( s.pLock==0 ){
close(s.fd);
return SQLITE_NOMEM;
}
*pResult = s;
return SQLITE_OK;
#endif
#if OS_WIN
@@ -246,7 +336,7 @@ int sqliteOsTempFileName(char *zBuf){
sprintf(zBuf, "%s/sqlite_", zDir);
j = strlen(zBuf);
for(i=0; i<15; i++){
int n = rand() % sizeof(zChars);
int n = sqliteRandomByte() % (sizeof(zChars)-1);
zBuf[j++] = zChars[n];
}
zBuf[j] = 0;
@@ -264,7 +354,7 @@ int sqliteOsTempFileName(char *zBuf){
sprintf(zBuf, "%s/sqlite_", zTempPath);
j = strlen(zBuf);
for(i=0; i<15; i++){
int n = rand() % sizeof(zChars);
int n = sqliteRandomByte() % sizeof(zChars);
zBuf[j++] = zChars[n];
}
zBuf[j] = 0;
@@ -279,7 +369,10 @@ int sqliteOsTempFileName(char *zBuf){
*/
int sqliteOsClose(OsFile id){
#if OS_UNIX
close(id);
close(id.fd);
sqliteOsEnterMutex();
releaseLockInfo(id.pLock);
sqliteOsLeaveMutex();
return SQLITE_OK;
#endif
#if OS_WIN
@@ -295,7 +388,7 @@ int sqliteOsClose(OsFile id){
int sqliteOsRead(OsFile id, void *pBuf, int amt){
#if OS_UNIX
int got;
got = read(id, pBuf, amt);
got = read(id.fd, pBuf, amt);
if( got<0 ) got = 0;
return got==amt ? SQLITE_OK : SQLITE_IOERR;
#endif
@@ -315,7 +408,7 @@ int sqliteOsRead(OsFile id, void *pBuf, int amt){
int sqliteOsWrite(OsFile id, const void *pBuf, int amt){
#if OS_UNIX
int wrote;
wrote = write(id, pBuf, amt);
wrote = write(id.fd, pBuf, amt);
if( wrote<amt ) return SQLITE_FULL;
return SQLITE_OK;
#endif
@@ -333,7 +426,7 @@ int sqliteOsWrite(OsFile id, const void *pBuf, int amt){
*/
int sqliteOsSeek(OsFile id, int offset){
#if OS_UNIX
lseek(id, offset, SEEK_SET);
lseek(id.fd, offset, SEEK_SET);
return SQLITE_OK;
#endif
#if OS_WIN
@@ -347,7 +440,7 @@ int sqliteOsSeek(OsFile id, int offset){
*/
int sqliteOsSync(OsFile id){
#if OS_UNIX
return fsync(id)==0 ? SQLITE_OK : SQLITE_IOERR;
return fsync(id.fd)==0 ? SQLITE_OK : SQLITE_IOERR;
#endif
#if OS_WIN
return FlushFileBuffers(id) ? SQLITE_OK : SQLITE_IOERR;
@@ -359,7 +452,7 @@ int sqliteOsSync(OsFile id){
*/
int sqliteOsTruncate(OsFile id, int nByte){
#if OS_UNIX
return ftruncate(id, nByte)==0 ? SQLITE_OK : SQLITE_IOERR;
return ftruncate(id.fd, nByte)==0 ? SQLITE_OK : SQLITE_IOERR;
#endif
#if OS_WIN
SetFilePointer(id, nByte, 0, FILE_BEGIN);
@@ -374,7 +467,7 @@ int sqliteOsTruncate(OsFile id, int nByte){
int sqliteOsFileSize(OsFile id, int *pSize){
#if OS_UNIX
struct stat buf;
if( fstat(id, &buf)!=0 ){
if( fstat(id.fd, &buf)!=0 ){
return SQLITE_IOERR;
}
*pSize = buf.st_size;
@@ -386,21 +479,41 @@ int sqliteOsFileSize(OsFile id, int *pSize){
#endif
}
/*
** Get a read or write lock on a file.
*/
int sqliteOsLock(OsFile id, int wrlock){
#if OS_UNIX
int rc;
struct flock lock;
lock.l_type = wrlock ? F_WRLCK : F_RDLCK;
lock.l_whence = SEEK_SET;
lock.l_start = lock.l_len = 0L;
rc = fcntl(id, F_SETLK, &lock);
if( rc ){
fcntl(id, F_GETLK, &lock); /* For debugging */
int needSysLock;
sqliteOsEnterMutex();
if( wrlock ){
if( id.pLock->cnt!=0 ){
rc = SQLITE_BUSY;
}else{
rc = SQLITE_OK;
id.pLock->cnt = -1;
needSysLock = 1;
}
}else{
if( id.pLock<0 ){
rc = SQLITE_BUSY;
}else{
rc = SQLITE_OK;
needSysLock = id.pLock->cnt==0;
id.pLock->cnt++;
}
}
return rc==0 ? SQLITE_OK : SQLITE_BUSY;
sqliteOsLeaveMutex();
if( rc==SQLITE_OK && needSysLock ){
struct flock lock;
lock.l_type = wrlock ? F_WRLCK : F_RDLCK;
lock.l_whence = SEEK_SET;
lock.l_start = lock.l_len = 0L;
rc = fcntl(id.fd, F_SETLK, &lock)==0 ? SQLITE_OK : SQLITE_BUSY;
}
return rc;
#endif
#if OS_WIN
if( !LockFile(id, 0, 0, 1024, 0) ){
@@ -416,12 +529,28 @@ int sqliteOsLock(OsFile id, int wrlock){
int sqliteOsUnlock(OsFile id){
#if OS_UNIX
int rc;
struct flock lock;
lock.l_type = F_UNLCK;
lock.l_whence = SEEK_SET;
lock.l_start = lock.l_len = 0L;
rc = fcntl(id, F_SETLK, &lock);
return rc==0 ? SQLITE_OK : SQLITE_IOERR;
int needSysUnlock;
sqliteOsEnterMutex();
if( id.pLock->cnt<0 ){
needSysUnlock = 1;
id.pLock->cnt = 0;
}else if( id.pLock->cnt>0 ){
id.pLock->cnt--;
needSysUnlock = id.pLock->cnt==0;
}else{
rc = SQLITE_OK;
needSysUnlock = 0;
}
sqliteOsLeaveMutex();
if( needSysUnlock ){
struct flock lock;
lock.l_type = F_UNLCK;
lock.l_whence = SEEK_SET;
lock.l_start = lock.l_len = 0L;
rc = fcntl(id.fd, F_SETLK, &lock)==0 ? SQLITE_OK : SQLITE_IOERR;
}
return rc;
#endif
#if OS_WIN
return UnlockFile(id, 0, 0, 1024, 0) ? SQLITE_OK : SQLITE_IOERR;
@@ -469,3 +598,24 @@ int sqliteOsSleep(int ms){
return ms;
#endif
}
/*
** The following pair of routine implement mutual exclusion for
** multi-threaded processes. Only a single thread is allowed to
** executed code that is surrounded by EnterMutex() and LeaveMutex().
**
** SQLite uses only a single Mutex. There is not much critical
** code and what little there is executes quickly and without blocking.
**
****** TBD: The mutex is currently unimplemented. Until it is
****** implemented, SQLite is not threadsafe.
*/
static int inMutex = 0;
void sqliteOsEnterMutex(){
assert( !inMutex );
inMutex = 1;
}
void sqliteOsLeaveMutex(){
assert( inMutex );
inMutex = 0;
}