SQLite

** file is unlocked.  cnt==-1 means the file has an exclusive lock.
** cnt>0 means there are cnt shared locks on the file.
**
** Any attempt to lock or unlock a file first checks the locking
** 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.
*/

/*
** An instance of the following structure serves as the key used
** to locate a particular lockInfo structure given its inode.  Note
** that we have to include the process ID as part of the key.  On some
** threading implementations (ex: linux), each thread has a separate
** process ID.
*/
struct lockKey {
  dev_t dev;   /* Device number */
  ino_t ino;   /* Inode number */
  pid_t pid;   /* Process ID */
};

/*
** 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 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() */
};

/* 
** 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 };
static Hash openHash = { SQLITE_HASH_BINARY, 0, 0, 0, 0, 0 };




































/*
** Release a lockInfo structure previously allocated by findLockInfo().
*/
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 **/

/*
** If we compile with the SQLITE_TEST macro set, then the following block
** of code will give us the ability to simulate a disk I/O error.  This
** is used for testing the I/O recovery logic.
*/

*/
int sqliteOsOpenReadWrite(
  const char *zFilename,
  OsFile *id,
  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 ){
    id->fd = open(zFilename, O_RDONLY|O_LARGEFILE|O_BINARY);
    if( id->fd<0 ){
      return SQLITE_CANTOPEN; 
    }
    *pReadonly = 1;
  }else{
    *pReadonly = 0;
  }
  sqliteOsEnterMutex();
  rc = findLockInfo(id->fd, &id->pLock, &id->pOpen);
  sqliteOsLeaveMutex();
  if( rc ){
    close(id->fd);
    return SQLITE_NOMEM;
  }
  id->locked = 0;
  TRACE3("OPEN    %-3d %s\n", id->fd, zFilename);
  OpenCounter(+1);
  return SQLITE_OK;

**
** On success, write the file handle into *id and return SQLITE_OK.
**
** On failure, return SQLITE_CANTOPEN.
*/
int sqliteOsOpenExclusive(const char *zFilename, OsFile *id, int delFlag){
#if OS_UNIX
  int rc;
  if( access(zFilename, 0)==0 ){
    return SQLITE_CANTOPEN;
  }
  id->dirfd = -1;
  id->fd = open(zFilename,
                O_RDWR|O_CREAT|O_EXCL|O_NOFOLLOW|O_LARGEFILE|O_BINARY, 0600);
  if( id->fd<0 ){
    return SQLITE_CANTOPEN;
  }
  sqliteOsEnterMutex();
  rc = findLockInfo(id->fd, &id->pLock, &id->pOpen);
  sqliteOsLeaveMutex();
  if( rc ){
    close(id->fd);
    unlink(zFilename);
    return SQLITE_NOMEM;
  }
  id->locked = 0;
  if( delFlag ){
    unlink(zFilename);

**
** On success, write the file handle into *id and return SQLITE_OK.
**
** On failure, return SQLITE_CANTOPEN.
*/
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();
  rc = findLockInfo(id->fd, &id->pLock, &id->pOpen);
  sqliteOsLeaveMutex();
  if( rc ){
    close(id->fd);
    return SQLITE_NOMEM;
  }
  id->locked = 0;
  TRACE3("OPEN-RO %-3d %s\n", id->fd, zFilename);
  OpenCounter(+1);
  return SQLITE_OK;

    if( !sqliteOsFileExists(zBuf) ) break;
  }
#endif
  return SQLITE_OK; 
}

/*
** Close a file.
*/
int sqliteOsClose(OsFile *id){
#if OS_UNIX
  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);
  return SQLITE_OK;
#endif
#if OS_WIN
  CloseHandle(id->h);

#if OS_UNIX
  int rc;
  sqliteOsEnterMutex();
  if( id->pLock->cnt>0 ){
    if( !id->locked ){
      id->pLock->cnt++;
      id->locked = 1;
      id->pOpen->nLock++;
    }
    rc = SQLITE_OK;
  }else if( id->locked || id->pLock->cnt==0 ){
    struct flock lock;
    int s;
    lock.l_type = F_RDLCK;
    lock.l_whence = SEEK_SET;
    lock.l_start = lock.l_len = 0L;
    s = fcntl(id->fd, F_SETLK, &lock);
    if( s!=0 ){
      rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
    }else{
      rc = SQLITE_OK;
      if( !id->locked ){
        id->pOpen->nLock++;
        id->locked = 1;
      }
      id->pLock->cnt = 1;
    }
  }else{
    rc = SQLITE_BUSY;
  }
  sqliteOsLeaveMutex();
  return rc;
#endif

    lock.l_whence = SEEK_SET;
    lock.l_start = lock.l_len = 0L;
    s = fcntl(id->fd, F_SETLK, &lock);
    if( s!=0 ){
      rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
    }else{
      rc = SQLITE_OK;
      if( !id->locked ){
        id->pOpen->nLock++;
        id->locked = 1;
      }
      id->pLock->cnt = -1;
    }
  }else{
    rc = SQLITE_BUSY;
  }
  sqliteOsLeaveMutex();
  return rc;
#endif

    s = fcntl(id->fd, F_SETLK, &lock);
    if( s!=0 ){
      rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
    }else{
      rc = SQLITE_OK;
      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;
#endif
#if OS_WIN
  int rc;

#if OS_UNIX
# include <sys/types.h>
# include <sys/stat.h>
# include <fcntl.h>
# include <unistd.h>
  typedef struct OsFile OsFile;
  struct OsFile {
    struct openCnt *pOpen;    /* Info about all open fd's on this inode */
    struct lockInfo *pLock;   /* Info about locks on this inode */
    int fd;                   /* The file descriptor */
    int locked;               /* True if this instance holds the lock */
    int dirfd;                /* File descriptor for the directory */
  };
# define SQLITE_TEMPNAME_SIZE 200
# if defined(HAVE_USLEEP) && HAVE_USLEEP
#  define SQLITE_MIN_SLEEP_MS 1
# else
#  define SQLITE_MIN_SLEEP_MS 1000
# endif