diff options
Diffstat (limited to 'src/os_win.c')
| -rw-r--r-- | src/os_win.c | 46 |
1 files changed, 4 insertions, 42 deletions
diff --git a/src/os_win.c b/src/os_win.c index 1134eeea2..bc8e02c37 100644 --- a/src/os_win.c +++ b/src/os_win.c @@ -314,47 +314,6 @@ int sqlite3OsFileSize(OsFile *id, off_t *pSize){ } /* -** Windows file locking notes: -** -** We cannot use LockFileEx() or UnlockFileEx() on Win95/98/ME because -** those functions are not available. So we use only LockFile() and -** UnlockFile(). -** -** LockFile() prevents not just writing but also reading by other processes. -** (This is a design error on the part of Windows, but there is nothing -** we can do about that.) So the region used for locking is at the -** end of the file where it is unlikely to ever interfere with an -** actual read attempt. -** -** A SHARED_LOCK is obtained by locking a single randomly-chosen -** byte out of a specific range of bytes. The lock byte is obtained at -** random so two separate readers can probably access the file at the -** same time, unless they are unlucky and choose the same lock byte. -** An EXCLUSIVE_LOCK is obtained by locking all bytes in the range. -** There can only be one writer. A RESERVED_LOCK is obtained by locking -** a single byte of the file that is designated as the reserved lock byte. -** A PENDING_LOCK is obtained by locking a designated byte different from -** the RESERVED_LOCK byte. -** -** 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. -** -** The following #defines specify the range of bytes used for locking. -** SHARED_SIZE is the number of bytes available in the pool from which -** a random byte is selected for a shared lock. The pool of bytes for -** shared locks begins at SHARED_FIRST. -*/ -#define SHARED_SIZE 10238 -#define SHARED_FIRST (0x3fffffff - (SHARED_SIZE - 1)) -#define RESERVED_BYTE (SHARED_FIRST - 1) -#define PENDING_BYTE (RESERVED_BYTE - 1) - -/* ** Return true (non-zero) if we are running under WinNT, Win2K or WinXP. ** Return false (zero) for Win95, Win98, or WinME. ** @@ -531,13 +490,16 @@ int sqlite3OsCheckWriteLock(OsFile *id){ int rc; if( id->locktype>=RESERVED_LOCK ){ rc = 1; + TRACE3("TEST WR-LOCK %d %d (local)\n", id->h, rc); }else{ rc = LockFile(id->h, RESERVED_BYTE, 0, 1, 0); if( rc ){ UnlockFile(id->h, RESERVED_BYTE, 0, 1, 0); } + rc = !rc; + TRACE3("TEST WR-LOCK %d %d (remote)\n", id->h, rc); } - return 0; + return rc; } /* |