SQLite

/*
** Include code that is common to all os_*.c files
*/
#include "os_common.h"


/*
** Here is the dirt on POSIX advisory locks:  ANSI STD 1003.1 (1996)
** section 6.5.2.2 lines 483 through 490 specify that when a process
** sets or clears a lock, that operation overrides any prior locks set
** by the same process.  It does not explicitly say so, but this implies
** that it overrides locks set by the same process using a different
** file descriptor.  Consider this test case:

** 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 sqlite3OsReadLock(OsFile *id){
  int rc;
  return sqlite3OsLock(id, SHARED_LOCK);
}

/*
** 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 sqlite3OsWriteLock(OsFile *id){
  int rc;
  return sqlite3OsLock(id, EXCLUSIVE_LOCK);
}

/*
** Lock the file with the lock specified by parameter locktype - one
** of the following:
**

  ** has a SHARED or RESERVED lock, then increment reference counts and
  ** return SQLITE_OK.
  */
  if( locktype==SHARED_LOCK && 
      (pLock->locktype==SHARED_LOCK || pLock->locktype==RESERVED_LOCK) ){
    assert( locktype==SHARED_LOCK );
    assert( id->locked==0 );

    id->locked = SHARED_LOCK;
    pLock->cnt++;
    id->pOpen->nLock++;
    goto end_lock;
  }

  lock.l_len = 1L;
  lock.l_whence = SEEK_SET;

  /* If control gets to this point, then actually go ahead and make
  ** operating system calls for the specified lock.
  */
  if( locktype==SHARED_LOCK ){
    assert( pLock->cnt==0 );
    assert( id->pOpen->nLock==0 );
    assert( pLock->locktype==0 );
  
    /* Grab a read-lock on byte 2. This ensures that no other process
    ** has a PENDING lock.
    */
    lock.l_type = F_RDLCK;
    lock.l_start = 2;

    lock.l_start = 2;
    lock.l_type = F_UNLCK;
    fcntl(id->fd, F_SETLK, &lock);
    if( s ){
      rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
    }else{
      id->locked = SHARED_LOCK;
      id->pOpen->nLock = 1;
      pLock->cnt = 1;
    }
  }else{
    /* The request was for a RESERVED, PENDING or EXCLUSIVE lock.  It is
    ** assumed that there is a SHARED or greater lock on the file
    ** already.
    */

    }
    s = fcntl(id->fd, F_SETLK, &lock);
    if( s ){
      rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
    }
  }
  

  id->locked = locktype;
  pLock->locktype = locktype;
  assert(pLock->locktype==RESERVED_LOCK||(id->pOpen->nLock==1&&pLock->cnt==1));


end_lock:
  sqlite3OsLeaveMutex();
  return rc;
}

/*
** 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 sqlite3OsUnlock(OsFile *id){
  int rc;
  if( !id->locked ) return SQLITE_OK;

  sqlite3OsEnterMutex();
  assert( id->pLock->cnt!=0 );
  if( id->pLock->cnt>1 ){
    id->locked = 0;
    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;
      id->pLock->locktype = 0;
      id->locked = 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--;

# 2003 December 18
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this script is multithreading behavior
#
# $Id: thread1.test,v 1.3 2004/02/11 02:18:07 drh Exp $


set testdir [file dirname $argv0]
source $testdir/tester.tcl

# Skip this whole file if the thread testing code is not enabled
#

  thread_result B
} SQLITE_OK
do_test thread1-2.9 {
  thread_step C
  thread_result C
} SQLITE_DONE
do_test thread1-2.10 {
  execsql {SELECT * FROM t2}
} {98 99}
do_test thread1-2.11 {
  thread_finalize C
  thread_result C
} SQLITE_OK




thread_halt *   
finish_test