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/* -----------------------------------------------------------------------------
*
* (c) The GHC Team, 2007
*
* File locking support as required by Haskell
*
* ---------------------------------------------------------------------------*/
#include "rts/PosixSource.h"
#include "Rts.h"
#include "FileLock.h"
#include "Hash.h"
#include "RtsUtils.h"
#include <sys/types.h>
#include <unistd.h>
#include <errno.h>
typedef struct {
StgWord64 device;
StgWord64 inode;
int readers; // >0 : readers, <0 : writers
} Lock;
// Two hash tables. The first maps objects (device/inode pairs) to
// Lock objects containing the number of active readers or writers. The
// second maps file descriptors or file handles to lock objects, so that we can
// unlock by FD or HANDLE without needing to fstat() again.
static HashTable *obj_hash;
static HashTable *key_hash;
#if defined(THREADED_RTS)
static Mutex file_lock_mutex;
#endif
STATIC_INLINE int cmpLocks(StgWord w1, StgWord w2)
{
Lock *l1 = (Lock *)w1;
Lock *l2 = (Lock *)w2;
return (l1->device == l2->device && l1->inode == l2->inode);
}
STATIC_INLINE int hashLock(const HashTable *table, StgWord w)
{
Lock *l = (Lock *)w;
StgWord key = l->inode ^ (l->inode >> 32) ^ l->device ^ (l->device >> 32);
// Just xor all 32-bit words of inode and device, hope this is good enough.
return hashWord(table, key);
}
void
initFileLocking(void)
{
obj_hash = allocHashTable();
key_hash = allocHashTable(); /* ordinary word-based table */
#if defined(THREADED_RTS)
initMutex(&file_lock_mutex);
#endif
}
static void
freeLock(void *lock)
{
stgFree(lock);
}
void
freeFileLocking(void)
{
freeHashTable(obj_hash, freeLock);
freeHashTable(key_hash, NULL);
#if defined(THREADED_RTS)
closeMutex(&file_lock_mutex);
#endif
}
int
lockFile(StgWord64 id, StgWord64 dev, StgWord64 ino, int for_writing)
{
Lock key, *lock;
ACQUIRE_LOCK(&file_lock_mutex);
key.device = dev;
key.inode = ino;
lock = lookupHashTable_(obj_hash, (StgWord)&key, hashLock, cmpLocks);
if (lock == NULL)
{
lock = stgMallocBytes(sizeof(Lock), "lockFile");
lock->device = dev;
lock->inode = ino;
lock->readers = for_writing ? -1 : 1;
insertHashTable_(obj_hash, (StgWord)lock, (void *)lock, hashLock);
insertHashTable(key_hash, id, lock);
RELEASE_LOCK(&file_lock_mutex);
return 0;
}
else
{
// single-writer/multi-reader locking:
if (for_writing || lock->readers < 0) {
RELEASE_LOCK(&file_lock_mutex);
return -1;
}
insertHashTable(key_hash, id, lock);
lock->readers++;
RELEASE_LOCK(&file_lock_mutex);
return 0;
}
}
int
unlockFile(StgWord64 id)
{
Lock *lock;
ACQUIRE_LOCK(&file_lock_mutex);
lock = lookupHashTable(key_hash, id);
if (lock == NULL) {
// errorBelch("unlockFile: key %d not found", key);
// This is normal: we didn't know when calling unlockFile
// whether this FD referred to a locked file or not.
RELEASE_LOCK(&file_lock_mutex);
return 1;
}
if (lock->readers < 0) {
lock->readers++;
} else {
lock->readers--;
}
if (lock->readers == 0) {
removeHashTable_(obj_hash, (StgWord)lock, NULL, hashLock, cmpLocks);
stgFree(lock);
}
removeHashTable(key_hash, id, NULL);
RELEASE_LOCK(&file_lock_mutex);
return 0;
}
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