1 /* Copyright 2012, Google Inc. 2 * All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions are 6 * met: 7 * 8 * * Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * * Redistributions in binary form must reproduce the above 11 * copyright notice, this list of conditions and the following 12 * disclaimer in the documentation and/or other materials provided 13 * with the distribution. 14 * * Neither the name of Google Inc. nor the names of its 15 * contributors may be used to endorse or promote products derived 16 * from this software without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 22 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 */ 30 31 #ifndef IPC_LOCK_H__ 32 #define IPC_LOCK_H__ 33 34 struct ipc_lock { 35 int is_held; /* internal */ 36 const char *filename; /* provided by the developer */ 37 int fd; /* internal */ 38 }; 39 40 /* don't use C99 initializers here, so this can be used in C++ code */ 41 #define LOCKFILE_INIT(lockfile) \ 42 { \ 43 0, /* is_held */ \ 44 lockfile, /* filename */ \ 45 -1, /* fd */ \ 46 } 47 48 /* 49 * acquire_lock: acquire a lock 50 * 51 * timeout <0 = no timeout (try forever) 52 * timeout 0 = do not wait (return immediately) 53 * timeout >0 = wait up to $timeout milliseconds (subject to kernel scheduling) 54 * 55 * return 0 = lock acquired 56 * return >0 = lock was already held 57 * return <0 = failed to acquire lock 58 */ 59 extern int acquire_lock(struct ipc_lock *lock, int timeout_msecs); 60 61 /* 62 * release_lock: release a lock 63 * 64 * returns 0 if lock was released successfully 65 * returns -1 if lock had not been held before the call 66 */ 67 extern int release_lock(struct ipc_lock *lock); 68 69 #endif /* IPC_LOCK_H__ */ 70