| /* |
| * Copyright (C) 2008 The Android Open Source Project |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * * Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * * Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in |
| * the documentation and/or other materials provided with the |
| * distribution. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, |
| * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS |
| * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED |
| * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, |
| * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT |
| * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| * SUCH DAMAGE. |
| */ |
| |
| /* implement flockfile(), ftrylockfile() and funlockfile() |
| * |
| * we can't use the OpenBSD implementation which uses kernel-specific |
| * APIs not available on Linux. |
| * |
| * Ideally, this would be trivially implemented by adding a |
| * pthread_mutex_t field to struct __sFILE as defined in |
| * <stdio.h>. |
| * |
| * However, since we don't want to bring pthread into the mix |
| * as well as change the size of a public API/ABI structure, |
| * we're going to store the data out-of-band. |
| * |
| * we use a hash-table to map FILE* pointers to recursive mutexes |
| * fclose() will call __fremovelock() defined below to remove |
| * a pointer from the table. |
| * |
| * the behaviour, if fclose() is called while the corresponding |
| * file is locked is totally undefined. |
| */ |
| #include <stdio.h> |
| #include <pthread.h> |
| #include <string.h> |
| |
| /* a node in the hash table */ |
| typedef struct FileLock { |
| struct FileLock* next; |
| FILE* file; |
| pthread_mutex_t mutex; |
| } FileLock; |
| |
| /* use a static hash table. We assume that we're not going to |
| * lock a really large number of FILE* objects on an embedded |
| * system. |
| */ |
| #define FILE_LOCK_BUCKETS 32 |
| |
| typedef struct { |
| pthread_mutex_t lock; |
| FileLock* buckets[ FILE_LOCK_BUCKETS ]; |
| } LockTable; |
| |
| static LockTable* _lockTable; |
| static pthread_once_t _lockTable_once = PTHREAD_ONCE_INIT; |
| |
| static void |
| lock_table_init( void ) |
| { |
| _lockTable = malloc(sizeof(*_lockTable)); |
| if (_lockTable != NULL) { |
| pthread_mutex_init(&_lockTable->lock, NULL); |
| memset(_lockTable->buckets, 0, sizeof(_lockTable->buckets)); |
| } |
| } |
| |
| static LockTable* |
| lock_table_lock( void ) |
| { |
| pthread_once( &_lockTable_once, lock_table_init ); |
| pthread_mutex_lock( &_lockTable->lock ); |
| return _lockTable; |
| } |
| |
| static void |
| lock_table_unlock( LockTable* t ) |
| { |
| pthread_mutex_unlock( &t->lock ); |
| } |
| |
| static FileLock** |
| lock_table_lookup( LockTable* t, FILE* f ) |
| { |
| uint32_t hash = (uint32_t)(void*)f; |
| FileLock** pnode; |
| |
| hash = (hash >> 2) ^ (hash << 17); |
| pnode = &t->buckets[hash % FILE_LOCK_BUCKETS]; |
| for (;;) { |
| FileLock* node = *pnode; |
| if (node == NULL || node->file == f) |
| break; |
| pnode = &node->next; |
| } |
| return pnode; |
| } |
| |
| void |
| flockfile(FILE * fp) |
| { |
| LockTable* t = lock_table_lock(); |
| |
| if (t != NULL) { |
| FileLock** lookup = lock_table_lookup(t, fp); |
| FileLock* lock = *lookup; |
| |
| if (lock == NULL) { |
| pthread_mutexattr_t attr; |
| |
| /* create a new node in the hash table */ |
| lock = malloc(sizeof(*lock)); |
| if (lock == NULL) { |
| lock_table_unlock(t); |
| return; |
| } |
| lock->next = NULL; |
| lock->file = fp; |
| |
| pthread_mutexattr_init(&attr); |
| pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE); |
| pthread_mutex_init( &lock->mutex, &attr ); |
| |
| *lookup = lock; |
| } |
| lock_table_unlock(t); |
| |
| /* we assume that another thread didn't destroy 'lock' |
| * by calling fclose() on the FILE*. This can happen if |
| * the client is *really* buggy, but we don't care about |
| * such code here. |
| */ |
| pthread_mutex_lock(&lock->mutex); |
| } |
| } |
| |
| |
| int |
| ftrylockfile(FILE *fp) |
| { |
| int ret = -1; |
| LockTable* t = lock_table_lock(); |
| |
| if (t != NULL) { |
| FileLock** lookup = lock_table_lookup(t, fp); |
| FileLock* lock = *lookup; |
| |
| lock_table_unlock(t); |
| |
| /* see above comment about why we assume that 'lock' can |
| * be accessed from here |
| */ |
| if (lock != NULL && !pthread_mutex_trylock(&lock->mutex)) { |
| ret = 0; /* signal success */ |
| } |
| } |
| return ret; |
| } |
| |
| void |
| funlockfile(FILE * fp) |
| { |
| LockTable* t = lock_table_lock(); |
| |
| if (t != NULL) { |
| FileLock** lookup = lock_table_lookup(t, fp); |
| FileLock* lock = *lookup; |
| |
| if (lock != NULL) |
| pthread_mutex_unlock(&lock->mutex); |
| |
| lock_table_unlock(t); |
| } |
| } |
| |
| |
| /* called from fclose() to remove the file lock */ |
| __LIBC_HIDDEN__ void |
| __fremovelock(FILE* fp) |
| { |
| LockTable* t = lock_table_lock(); |
| |
| if (t != NULL) { |
| FileLock** lookup = lock_table_lookup(t, fp); |
| FileLock* lock = *lookup; |
| |
| if (lock != NULL) { |
| *lookup = lock->next; |
| lock->file = NULL; |
| } |
| lock_table_unlock(t); |
| free(lock); |
| } |
| } |