os_unix.c

sqlite嵌入式数据库源码

        pLock->locktype = NO_LOCK;
      }else{
        rc = SQLITE_IOERR;  /* This should never happen */
      }
    }

    /* 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.
    */
    pOpen = pFile->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]);
      }
      free(pOpen->aPending);
      pOpen->nPending = 0;
      pOpen->aPending = 0;
    }
  }
  sqlite3OsLeaveMutex();
  pFile->locktype = locktype;
  return rc;
}

/*
** Close a file.
*/
static int unixClose(OsFile **pId){
  unixFile *id = (unixFile*)*pId;

  if( !id ) return SQLITE_OK;
  unixUnlock(*pId, NO_LOCK);
  if( id->dirfd>=0 ) close(id->dirfd);
  id->dirfd = -1;
  sqlite3OsEnterMutex();

  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;
    aNew = realloc( pOpen->aPending, (pOpen->nPending+1)*sizeof(int) );
    if( aNew==0 ){
      /* If a malloc fails, just leak the file descriptor */
    }else{
      pOpen->aPending = aNew;
      pOpen->aPending[pOpen->nPending] = id->h;
      pOpen->nPending++;
    }
  }else{
    /* There are no outstanding locks so we can close the file immediately */
    close(id->h);
  }
  releaseLockInfo(id->pLock);
  releaseOpenCnt(id->pOpen);

  sqlite3OsLeaveMutex();
  id->isOpen = 0;
  TRACE2("CLOSE   %-3d\n", id->h);
  OpenCounter(-1);
  sqlite3ThreadSafeFree(id);
  *pId = 0;
  return SQLITE_OK;
}

/*
** 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 *sqlite3UnixFullPathname(const char *zRelative){
  char *zFull = 0;
  if( zRelative[0]=='/' ){
    sqlite3SetString(&zFull, zRelative, (char*)0);
  }else{
    char *zBuf = sqliteMalloc(5000);
    if( zBuf==0 ){
      return 0;
    }
    zBuf[0] = 0;
    sqlite3SetString(&zFull, getcwd(zBuf, 5000), "/", zRelative,
                    (char*)0);
    sqliteFree(zBuf);
  }

#if 0
  /*
  ** Remove "/./" path elements and convert "/A/./" path elements
  ** to just "/".
  */
  if( zFull ){
    int i, j;
    for(i=j=0; zFull[i]; i++){
      if( zFull[i]=='/' ){
        if( zFull[i+1]=='/' ) continue;
        if( zFull[i+1]=='.' && zFull[i+2]=='/' ){
          i += 1;
          continue;
        }
        if( zFull[i+1]=='.' && zFull[i+2]=='.' && zFull[i+3]=='/' ){
          while( j>0 && zFull[j-1]!='/' ){ j--; }
          i += 3;
          continue;
        }
      }
      zFull[j++] = zFull[i];
    }
    zFull[j] = 0;
  }
#endif

  return zFull;
}

/*
** Change the value of the fullsync flag in the given file descriptor.
*/
static void unixSetFullSync(OsFile *id, int v){
  ((unixFile*)id)->fullSync = v;
}

/*
** Return the underlying file handle for an OsFile
*/
static int unixFileHandle(OsFile *id){
  return ((unixFile*)id)->h;
}

/*
** Return an integer that indices the type of lock currently held
** by this handle.  (Used for testing and analysis only.)
*/
static int unixLockState(OsFile *id){
  return ((unixFile*)id)->locktype;
}

/*
** This vector defines all the methods that can operate on an OsFile
** for unix.
*/
static const IoMethod sqlite3UnixIoMethod = {
  unixClose,
  unixOpenDirectory,
  unixRead,
  unixWrite,
  unixSeek,
  unixTruncate,
  unixSync,
  unixSetFullSync,
  unixFileHandle,
  unixFileSize,
  unixLock,
  unixUnlock,
  unixLockState,
  unixCheckReservedLock,
};

/*
** Allocate memory for a unixFile.  Initialize the new unixFile
** to the value given in pInit and return a pointer to the new
** OsFile.  If we run out of memory, close the file and return NULL.
*/
static int allocateUnixFile(unixFile *pInit, OsFile **pId){
  unixFile *pNew;
  pInit->dirfd = -1;
  pInit->fullSync = 0;
  pInit->locktype = 0;
  pInit->offset = 0;
  SET_THREADID(pInit);
  pNew = sqlite3ThreadSafeMalloc( sizeof(unixFile) );
  if( pNew==0 ){
    close(pInit->h);
    sqlite3OsEnterMutex();
    releaseLockInfo(pInit->pLock);
    releaseOpenCnt(pInit->pOpen);
    sqlite3OsLeaveMutex();
    *pId = 0;
    return SQLITE_NOMEM;
  }else{
    *pNew = *pInit;
    pNew->pMethod = &sqlite3UnixIoMethod;
    *pId = (OsFile*)pNew;
    OpenCounter(+1);
    return SQLITE_OK;
  }
}


#endif /* SQLITE_OMIT_DISKIO */
/***************************************************************************
** Everything above deals with file I/O.  Everything that follows deals
** with other miscellanous aspects of the operating system interface
****************************************************************************/


/*
** 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 sqlite3UnixRandomSeed(char *zBuf){
  /* We have to initialize zBuf to prevent valgrind from reporting
  ** errors.  The reports issued by valgrind are incorrect - we would
  ** prefer that the randomness be increased by making use of the
  ** uninitialized space in zBuf - but valgrind errors tend to worry
  ** some users.  Rather than argue, it seems easier just to initialize
  ** the whole array and silence valgrind, even if that means less randomness
  ** in the random seed.
  **
  ** When testing, initializing zBuf[] to zero is all we do.  That means
  ** that we always use the same random number sequence.  This makes the
  ** tests repeatable.
  */
  memset(zBuf, 0, 256);
#if !defined(SQLITE_TEST)
  {
    int pid, fd;
    fd = open("/dev/urandom", O_RDONLY);
    if( fd<0 ){
      time_t t;
      time(&t);
      memcpy(zBuf, &t, sizeof(t));
      pid = getpid();
      memcpy(&zBuf[sizeof(time_t)], &pid, sizeof(pid));
    }else{
      read(fd, zBuf, 256);
      close(fd);
    }
  }
#endif
  return SQLITE_OK;
}

/*
** Sleep for a little while.  Return the amount of time slept.
** The argument is the number of milliseconds we want to sleep.
*/
int sqlite3UnixSleep(int ms){
#if defined(HAVE_USLEEP) && HAVE_USLEEP
  usleep(ms*1000);
  return ms;
#else
  sleep((ms+999)/1000);
  return 1000*((ms+999)/1000);
#endif
}

/*
** Static variables used for thread synchronization.
**
** inMutex      the nesting depth of the recursive mutex.  The thread
**              holding mutexMain can read this variable at any time.
**              But is must hold mutexAux to change this variable.  Other
**              threads must hold mutexAux to read the variable and can
**              never write.
**
** mutexOwner   The thread id of the thread holding mutexMain.  Same
**              access rules as for inMutex.
**
** mutexOwnerValid   True if the value in mutexOwner is valid.  The same
**                   access rules apply as for inMutex.
**
** mutexMain    The main mutex.  Hold this mutex in order to get exclusive
**              access to SQLite data structures.
**
** mutexAux     An auxiliary mutex needed to access variables defined above.
**
** Mutexes are always acquired in this order: mutexMain mutexAux.   It
** is not necessary to acquire mutexMain in order to get mutexAux - just
** do not attempt to acquire them in the reverse order: mutexAux mutexMain.
** Either get the mutexes with mutexMain first or get mutexAux only.
**
** When running on a platform where the three variables inMutex, mutexOwner,
** and mutexOwnerValid can be set atomically, the mutexAux is not required.
** On many systems, all three are 32-bit integers and writing to a 32-bit
** integer is atomic.  I think.  But there are no guarantees.  So it seems
** safer to protect them using mutexAux.
*/
static int inMutex = 0;
#ifdef SQLITE_UNIX_THREADS
static pthread_t mutexOwner;          /* Thread holding mutexMain */
static int mutexOwnerValid = 0;       /* True if mutexOwner is valid */
static pthread_mutex_t mutexMain = PTHREAD_MUTEX_INITIALIZER; /* The mutex */
static pthread_mutex_t mutexAux = PTHREAD_MUTEX_INITIALIZER;  /* Aux mutex */
#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.
**
** As of version 3.3.2, this mutex must be recursive.
*/
void sqlite3UnixEnterMutex(){
#ifdef SQLITE_UNIX_THREADS
  pthread_mutex_lock(&mutexAux);
  if( !mutexOwnerValid || !pthread_equal(mutexOwner, pthread_self()) ){
    pthread_mutex_unlock(&mutexAux);
    pthread_mutex_lock(&mutexMain);
    assert( inMutex==0 );
    assert( !mutexOwnerValid );
    pthread_mutex_lock(&mutexAux);
    mutexOwner = pthread_self();
    mutexOwnerValid = 1;
  }
  inMutex++;
  pthread_mutex_unlock(&mutexAux);
#else
  inMutex++;
#endif
}
void sqlite3UnixLeaveMutex(){
  assert( inMutex>0 );
#ifdef SQLITE_UNIX_THREADS
  pthread_mutex_lock(&mutexAux);
  inMutex--;
  assert( pthread_equal(mutexOwner, pthread_self()) );
  if( inMutex==0 ){
    assert( mutexOwnerValid );
    mutexOwnerValid = 0;
    pthread_mutex_unlock(&mutexMain);
  }
  pthread_mutex_unlock(&mutexAux);
#else
  inMutex--;
#endif
}

/*
** Return TRUE if the mutex is currently held.
**
** If the thisThrd parameter is true, return true only if the
** calling thread holds the mutex.  If the parameter is false, return
** true if any thread holds the mutex.
*/
int sqlite3UnixInMutex(int thisThrd){
#ifdef SQLITE_UNIX_THREADS
  int rc;
  pthread_mutex_lock(&mutexAux);
  rc = inMutex>0 && (thisThrd==0 || pthread_equal(mutexOwner,pthread_self()));
  pthread_mutex_unlock(&mutexAux);
  return rc;
#else
  return inMutex>0;
#endif
}

/*
** Remember the number of thread-specific-data blocks allocated.
** Use this to verify that we are not leaking thread-specific-data.
** Ticket #1601
*/
#ifdef SQLITE_TEST
int sqlite3_tsd_count = 0;
# ifdef SQLITE_UNIX_THREADS
    static pthread_mutex_t tsd_counter_mutex = PTHREAD_MUTEX_INITIALIZER;
#   define TSD_COUNTER(N) \
             pthread_mutex_lock(&tsd_counter_mutex); \
             sqlite3_tsd_count += N; \
             pthread_mutex_unlock(&tsd_counter_mutex);
# else
#   define TSD_COUNTER(N)  sqlite3_tsd_count += N
# endif
#else
# define TSD_COUNTER(N)  /* no-op */
#endif

/*
** If called with allocateFlag>0, then return a pointer to thread
** specific data for the current thread.  Allocate and zero the
** thread-specific data if it does not already exist.
**
** If called with allocateFlag==0, then check the current thread
** specific data.  Return it if it exists.  If it does not exist,
** then return NULL.
**
** If called with allocateFlag<0, check to see if the thread specific
** data is allocated and is all zero.  If it is then deallocate it.
** Return a pointer to the thread specific data or NULL if it is
** unallocated or gets deallocated.
*/
ThreadData *sqlite3UnixThreadSpecificData(int allocateFlag){
  static const ThreadData zeroData = {0};  /* Initializer to silence warnings
                                           ** from broken compilers */
#ifdef SQLITE_UNIX_THREADS
  static pthread_key_t key;
  static int keyInit = 0;
  ThreadData *pTsd;

  if( !keyInit ){
    sqlite3OsEnterMutex();
    if( !keyInit ){
      int rc;
      rc = pthread_key_create(&key, 0);
      if( rc ){
        sqlite3OsLeaveMutex();
        return 0;
      }
      keyInit = 1;
    }
    sqlite3OsLeaveMutex();
  }

  pTsd = pthread_getspecific(key);
  if( allocateFlag>0 ){
    if( pTsd==0 ){
      if( !sqlite3TestMallocFail() ){
        pTsd = sqlite3OsMalloc(sizeof(zeroData));
      }
#ifdef SQLITE_MEMDEBUG
      sqlite3_isFail = 0;
#endif
      if( pTsd ){
        *pTsd = zeroData;
        pthread_setspecific(key, pTsd);
        TSD_COUNTER(+1);
      }
    }
  }else if( pTsd!=0 && allocateFlag<0 
            && memcmp(pTsd, &zeroData, sizeof(ThreadData))==0 ){
    sqlite3OsFree(pTsd);
    pthread_setspecific(key, 0);
    TSD_COUNTER(-1);
    pTsd = 0;
  }
  return pTsd;
#else
  static ThreadData *pTsd = 0;
  if( allocateFlag>0 ){
    if( pTsd==0 ){
      if( !sqlite3TestMallocFail() ){
        pTsd = sqlite3OsMalloc( sizeof(zeroData) );
      }
#ifdef SQLITE_MEMDEBUG
      sqlite3_isFail = 0;
#endif
      if( pTsd ){
        *pTsd = zeroData;
        TSD_COUNTER(+1);
      }
    }
  }else if( pTsd!=0 && allocateFlag<0
            && memcmp(pTsd, &zeroData, sizeof(ThreadData))==0 ){
    sqlite3OsFree(pTsd);
    TSD_COUNTER(-1);
    pTsd = 0;
  }
  return pTsd;
#endif
}

/*
** The following variable, if set to a non-zero value, becomes the result
** returned from sqlite3OsCurrentTime().  This is used for testing.
*/
#ifdef SQLITE_TEST
int sqlite3_current_time = 0;
#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 sqlite3UnixCurrentTime(double *prNow){
#ifdef NO_GETTOD
  time_t t;
  time(&t);
  *prNow = t/86400.0 + 2440587.5;
#else
  struct timeval sNow;
  struct timezone sTz;  /* Not used */
  gettimeofday(&sNow, &sTz);
  *prNow = 2440587.5 + sNow.tv_sec/86400.0 + sNow.tv_usec/86400000000.0;
#endif
#ifdef SQLITE_TEST
  if( sqlite3_current_time ){
    *prNow = sqlite3_current_time/86400.0 + 2440587.5;
  }
#endif
  return 0;
}

#endif /* OS_UNIX */