os.c

SQLite 2.8.6 源代码,用来在Linux/Unix/Windows上编译安装.它是一个小型的数据库,但是非常好用,速度也快,一般的数据库查询之类的操作据统计比MySQL,PostgreSQL

** A database write lock is obtained by locking all bytes in the range.
** There can only be one writer.
**
** A lock is obtained on the first byte of the lock range before acquiring
** either a read lock or a write lock.  This prevents two processes from
** attempting to get a lock at a same time.  The semantics of 
** sqliteOsReadLock() require that if there is already a write lock, that
** lock is converted into a read lock atomically.  The lock on the first
** byte allows us to drop the old write lock and get the read lock without
** another process jumping into the middle and messing us up.  The same
** argument applies to sqliteOsWriteLock().
**
** On WinNT/2K/XP systems, LockFileEx() and UnlockFileEx() are available,
** which means we can use reader/writer locks.  When reader writer locks
** are used, the lock is placed on the same range of bytes that is used
** for probabilistic locking in Win95/98/ME.  Hence, the locking scheme
** will support two or more Win95 readers or two or more WinNT readers.
** But a single Win95 reader will lock out all WinNT readers and a single
** WinNT reader will lock out all other Win95 readers.
**
** Note: On MacOS we use the resource fork for locking.
**
** The following #defines specify the range of bytes used for locking.
** N_LOCKBYTE is the number of bytes available for doing the locking.
** The first byte used to hold the lock while the lock is changing does
** not count toward this number.  FIRST_LOCKBYTE is the address of
** the first byte in the range of bytes used for locking.
*/
#define N_LOCKBYTE       10239
#if OS_MAC
# define FIRST_LOCKBYTE   (0x000fffff - N_LOCKBYTE)
#else
# define FIRST_LOCKBYTE   (0xffffffff - N_LOCKBYTE)
#endif

/*
** Change the status of the lock on the file "id" to be a readlock.
** If the file was write locked, then this reduces the lock to a read.
** If the file was read locked, then this acquires a new read lock.
**
** Return SQLITE_OK on success and SQLITE_BUSY on failure.  If this
** library was compiled with large file support (LFS) but LFS is not
** available on the host, then an SQLITE_NOLFS is returned.
*/
int sqliteOsReadLock(OsFile *id){
#if OS_UNIX
  int rc;
  sqliteOsEnterMutex();
  if( id->pLock->cnt>0 ){
    if( !id->locked ){
      id->pLock->cnt++;
      id->locked = 1;
    }
    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;
      id->pLock->cnt = 1;
      id->locked = 1;
    }
  }else{
    rc = SQLITE_BUSY;
  }
  sqliteOsLeaveMutex();
  return rc;
#endif
#if OS_WIN
  int rc;
  if( id->locked>0 ){
    rc = SQLITE_OK;
  }else{
    int lk = (sqliteRandomInteger() & 0x7ffffff)%N_LOCKBYTE+1;
    int res;
    int cnt = 100;
    while( cnt-->0 && (res = LockFile(id->h, FIRST_LOCKBYTE, 0, 1, 0))==0 ){
      Sleep(1);
    }
    if( res ){
      UnlockFile(id->h, FIRST_LOCKBYTE+1, 0, N_LOCKBYTE, 0);
      if( isNT() ){
        OVERLAPPED ovlp;
        ovlp.Offset = FIRST_LOCKBYTE+1;
        ovlp.OffsetHigh = 0;
        ovlp.hEvent = 0;
        res = LockFileEx(id->h, LOCKFILE_FAIL_IMMEDIATELY, 
                          0, N_LOCKBYTE, 0, &ovlp);
      }else{
        res = LockFile(id->h, FIRST_LOCKBYTE+lk, 0, 1, 0);
      }
      UnlockFile(id->h, FIRST_LOCKBYTE, 0, 1, 0);
    }
    if( res ){
      id->locked = lk;
      rc = SQLITE_OK;
    }else{
      rc = SQLITE_BUSY;
    }
  }
  return rc;
#endif
#if OS_MAC
  int rc;
  if( id->locked>0 || id->refNumRF == -1 ){
    rc = SQLITE_OK;
  }else{
    int lk = (sqliteRandomInteger() & 0x7ffffff)%N_LOCKBYTE+1;
    OSErr res;
    int cnt = 5;
    ParamBlockRec params;
    memset(&params, 0, sizeof(params));
    params.ioParam.ioRefNum = id->refNumRF;
    params.ioParam.ioPosMode = fsFromStart;
    params.ioParam.ioPosOffset = FIRST_LOCKBYTE;
    params.ioParam.ioReqCount = 1;
    while( cnt-->0 && (res = PBLockRangeSync(&params))!=noErr ){
      UInt32 finalTicks;
      Delay(1, &finalTicks); /* 1/60 sec */
    }
    if( res == noErr ){
      params.ioParam.ioPosOffset = FIRST_LOCKBYTE+1;
      params.ioParam.ioReqCount = N_LOCKBYTE;
      PBUnlockRangeSync(&params);
      params.ioParam.ioPosOffset = FIRST_LOCKBYTE+lk;
      params.ioParam.ioReqCount = 1;
      res = PBLockRangeSync(&params);
      params.ioParam.ioPosOffset = FIRST_LOCKBYTE;
      params.ioParam.ioReqCount = 1;
      PBUnlockRangeSync(&params);
    }
    if( res == noErr ){
      id->locked = lk;
      rc = SQLITE_OK;
    }else{
      rc = SQLITE_BUSY;
    }
  }
  return rc;
#endif
}

/*
** Change the lock status to be an exclusive or write lock.  Return
** SQLITE_OK on success and SQLITE_BUSY on a failure.  If this
** library was compiled with large file support (LFS) but LFS is not
** available on the host, then an SQLITE_NOLFS is returned.
*/
int sqliteOsWriteLock(OsFile *id){
#if OS_UNIX
  int rc;
  sqliteOsEnterMutex();
  if( id->pLock->cnt==0 || (id->pLock->cnt==1 && id->locked==1) ){
    struct flock lock;
    int s;
    lock.l_type = F_WRLCK;
    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;
      id->pLock->cnt = -1;
      id->locked = 1;
    }
  }else{
    rc = SQLITE_BUSY;
  }
  sqliteOsLeaveMutex();
  return rc;
#endif
#if OS_WIN
  int rc;
  if( id->locked<0 ){
    rc = SQLITE_OK;
  }else{
    int res;
    int cnt = 100;
    while( cnt-->0 && (res = LockFile(id->h, FIRST_LOCKBYTE, 0, 1, 0))==0 ){
      Sleep(1);
    }
    if( res ){
      if( id->locked>0 ){
        if( isNT() ){
          UnlockFile(id->h, FIRST_LOCKBYTE+1, 0, N_LOCKBYTE, 0);
        }else{
          res = UnlockFile(id->h, FIRST_LOCKBYTE + id->locked, 0, 1, 0);
        }
      }
      if( res ){
        res = LockFile(id->h, FIRST_LOCKBYTE+1, 0, N_LOCKBYTE, 0);
      }else{
        res = 0;
      }
      UnlockFile(id->h, FIRST_LOCKBYTE, 0, 1, 0);
    }
    if( res ){
      id->locked = -1;
      rc = SQLITE_OK;
    }else{
      rc = SQLITE_BUSY;
    }
  }
  return rc;
#endif
#if OS_MAC
  int rc;
  if( id->locked<0 || id->refNumRF == -1 ){
    rc = SQLITE_OK;
  }else{
    OSErr res;
    int cnt = 5;
    ParamBlockRec params;
    memset(&params, 0, sizeof(params));
    params.ioParam.ioRefNum = id->refNumRF;
    params.ioParam.ioPosMode = fsFromStart;
    params.ioParam.ioPosOffset = FIRST_LOCKBYTE;
    params.ioParam.ioReqCount = 1;
    while( cnt-->0 && (res = PBLockRangeSync(&params))!=noErr ){
      UInt32 finalTicks;
      Delay(1, &finalTicks); /* 1/60 sec */
    }
    if( res == noErr ){
      params.ioParam.ioPosOffset = FIRST_LOCKBYTE + id->locked;
      params.ioParam.ioReqCount = 1;
      if( id->locked==0 
            || PBUnlockRangeSync(&params)==noErr ){
        params.ioParam.ioPosOffset = FIRST_LOCKBYTE+1;
        params.ioParam.ioReqCount = N_LOCKBYTE;
        res = PBLockRangeSync(&params);
      }else{
        res = afpRangeNotLocked;
      }
      params.ioParam.ioPosOffset = FIRST_LOCKBYTE;
      params.ioParam.ioReqCount = 1;
      PBUnlockRangeSync(&params);
    }
    if( res == noErr ){
      id->locked = -1;
      rc = SQLITE_OK;
    }else{
      rc = SQLITE_BUSY;
    }
  }
  return rc;
#endif
}

/*
** Unlock the given file descriptor.  If the file descriptor was
** not previously locked, then this routine is a no-op.  If this
** library was compiled with large file support (LFS) but LFS is not
** available on the host, then an SQLITE_NOLFS is returned.
*/
int sqliteOsUnlock(OsFile *id){
#if OS_UNIX
  int rc;
  if( !id->locked ) return SQLITE_OK;
  sqliteOsEnterMutex();
  assert( id->pLock->cnt!=0 );
  if( id->pLock->cnt>1 ){
    id->pLock->cnt--;
    rc = SQLITE_OK;
  }else{
    struct flock lock;
    int s;
    lock.l_type = F_UNLCK;
    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;
      id->pLock->cnt = 0;
    }
  }
  sqliteOsLeaveMutex();
  id->locked = 0;
  return rc;
#endif
#if OS_WIN
  int rc;
  if( id->locked==0 ){
    rc = SQLITE_OK;
  }else if( isNT() || id->locked<0 ){
    UnlockFile(id->h, FIRST_LOCKBYTE+1, 0, N_LOCKBYTE, 0);
    rc = SQLITE_OK;
    id->locked = 0;
  }else{
    UnlockFile(id->h, FIRST_LOCKBYTE+id->locked, 0, 1, 0);
    rc = SQLITE_OK;
    id->locked = 0;
  }
  return rc;
#endif
#if OS_MAC
  int rc;
  ParamBlockRec params;
  memset(&params, 0, sizeof(params));
  params.ioParam.ioRefNum = id->refNumRF;
  params.ioParam.ioPosMode = fsFromStart;
  if( id->locked==0 || id->refNumRF == -1 ){
    rc = SQLITE_OK;
  }else if( id->locked<0 ){
    params.ioParam.ioPosOffset = FIRST_LOCKBYTE+1;
    params.ioParam.ioReqCount = N_LOCKBYTE;
    PBUnlockRangeSync(&params);
    rc = SQLITE_OK;
    id->locked = 0;
  }else{
    params.ioParam.ioPosOffset = FIRST_LOCKBYTE+id->locked;
    params.ioParam.ioReqCount = 1;
    PBUnlockRangeSync(&params);
    rc = SQLITE_OK;
    id->locked = 0;
  }
  return rc;
#endif
}

/*
** Get information to seed the random number generator.  The seed
** is written into the buffer zBuf[256].  The calling function must
** supply a sufficiently large buffer.
*/
int sqliteOsRandomSeed(char *zBuf){
#ifdef SQLITE_TEST
  /* When testing, always use the same random number sequence.
  ** This makes the tests repeatable.
  */
  memset(zBuf, 0, 256);
#endif
#if OS_UNIX && !defined(SQLITE_TEST)
  int pid;
  time((time_t*)zBuf);
  pid = getpid();
  memcpy(&zBuf[sizeof(time_t)], &pid, sizeof(pid));
#endif
#if OS_WIN && !defined(SQLITE_TEST)
  GetSystemTime((LPSYSTEMTIME)zBuf);
#endif
#if OS_MAC
  int pid;
  Microseconds((UnsignedWide*)zBuf);
  pid = getpid();
  memcpy(&zBuf[sizeof(UnsignedWide)], &pid, sizeof(pid));
#endif
  return SQLITE_OK;
}

/*
** Sleep for a little while.  Return the amount of time slept.
*/
int sqliteOsSleep(int ms){
#if OS_UNIX
#if defined(HAVE_USLEEP) && HAVE_USLEEP
  usleep(ms*1000);
  return ms;
#else
  sleep((ms+999)/1000);
  return 1000*((ms+999)/1000);
#endif
#endif
#if OS_WIN
  Sleep(ms);
  return ms;
#endif
#if OS_MAC
  UInt32 finalTicks;
  UInt32 ticks = (((UInt32)ms+16)*3)/50;  /* 1/60 sec per tick */
  Delay(ticks, &finalTicks);
  return (int)((ticks*50)/3);
#endif
}

/*
** Macros used to determine whether or not to use threads.  The
** SQLITE_UNIX_THREADS macro is defined if we are synchronizing for
** Posix threads and SQLITE_W32_THREADS is defined if we are
** synchronizing using Win32 threads.
*/
#if OS_UNIX && defined(THREADSAFE) && THREADSAFE
# include <pthread.h>
# define SQLITE_UNIX_THREADS 1
#endif
#if OS_WIN && defined(THREADSAFE) && THREADSAFE
# define SQLITE_W32_THREADS 1
#endif
#if OS_MAC && defined(THREADSAFE) && THREADSAFE
# include <Multiprocessing.h>
# define SQLITE_MACOS_MULTITASKING 1
#endif

/*
** Static variables used for thread synchronization
*/
static int inMutex = 0;
#ifdef SQLITE_UNIX_THREADS
  static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
#endif
#ifdef SQLITE_W32_THREADS
  static CRITICAL_SECTION cs;
#endif
#ifdef SQLITE_MACOS_MULTITASKING
  static MPCriticalRegionID criticalRegion;
#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.
*/
void sqliteOsEnterMutex(){
#ifdef SQLITE_UNIX_THREADS
  pthread_mutex_lock(&mutex);
#endif
#ifdef SQLITE_W32_THREADS
  static int isInit = 0;
  while( !isInit ){
    static long lock = 0;
    if( InterlockedIncrement(&lock)==1 ){
      InitializeCriticalSection(&cs);
      isInit = 1;
    }else{
      Sleep(1);
    }
  }
  EnterCriticalSection(&cs);
#endif
#ifdef SQLITE_MACOS_MULTITASKING
  static volatile int notInit = 1;
  if( notInit ){
    if( notInit == 2 ) /* as close as you can get to thread safe init */
      MPYield();
    else{
      notInit = 2;
      MPCreateCriticalRegion(&criticalRegion);
      notInit = 0;
    }
  }
  MPEnterCriticalRegion(criticalRegion, kDurationForever);
#endif
  assert( !inMutex );
  inMutex = 1;
}
void sqliteOsLeaveMutex(){
  assert( inMutex );
  inMutex = 0;
#ifdef SQLITE_UNIX_THREADS
  pthread_mutex_unlock(&mutex);
#endif
#ifdef SQLITE_W32_THREADS
  LeaveCriticalSection(&cs);
#endif
#ifdef SQLITE_MACOS_MULTITASKING
  MPExitCriticalRegion(criticalRegion);
#endif
}

/*
** Turn a relative pathname into a full pathname.  Return a pointer
** to the full pathname stored in space obtained from sqliteMalloc().
** The calling function is responsible for freeing this space once it
** is no longer needed.
*/
char *sqliteOsFullPathname(const char *zRelative){
#if OS_UNIX
  char *zFull = 0;
  if( zRelative[0]=='/' ){
    sqliteSetString(&zFull, zRelative, 0);
  }else{
    char zBuf[5000];
    sqliteSetString(&zFull, getcwd(zBuf, sizeof(zBuf)), "/", zRelative, 0);
  }
  return zFull;
#endif
#if OS_WIN
  char *zNotUsed;
  char *zFull;
  int nByte;
  nByte = GetFullPathName(zRelative, 0, 0, &zNotUsed) + 1;
  zFull = sqliteMalloc( nByte );
  if( zFull==0 ) return 0;
  GetFullPathName(zRelative, nByte, zFull, &zNotUsed);
  return zFull;
#endif
#if OS_MAC
  char *zFull = 0;
  if( zRelative[0]==':' ){
    char zBuf[_MAX_PATH+1];
    sqliteSetString(&zFull, getcwd(zBuf, sizeof(zBuf)), &(zRelative[1]), 0);
  }else{
    if( strchr(zRelative, ':') ){
      sqliteSetString(&zFull, zRelative, 0);
    }else{
    char zBuf[_MAX_PATH+1];
      sqliteSetString(&zFull, getcwd(zBuf, sizeof(zBuf)), zRelative, 0);
    }
  }
  return zFull;
#endif
}

/*
** Find the current time (in Universal Coordinated Time).  Write the
** current time and date as a Julian Day number into *prNow and
** return 0.  Return 1 if the time and date cannot be found.
*/
int sqliteOsCurrentTime(double *prNow){
#if OS_UNIX
  time_t t;
  time(&t);
  *prNow = t/86400.0 + 2440587.5;
  return 0;
#endif
#if OS_WIN
  FILETIME ft;
  /* FILETIME structure is a 64-bit value representing the number of 
     100-nanosecond intervals since January 1, 1601 (= JD 2305813.5). 
  */
  double now;
  GetSystemTimeAsFileTime( &ft );
  now = ((double)ft.dwHighDateTime) * 4294967296.0; 
  *prNow = (now + ft.dwLowDateTime)/864000000000.0 + 2305813.5;
#endif
  return 0;

  return 1;
}