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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "rlz/lib/recursive_cross_process_lock_posix.h"
      6 
      7 #include <fcntl.h>
      8 #include <sys/file.h>
      9 #include <sys/stat.h>
     10 #include <sys/types.h>
     11 #include <unistd.h>
     12 
     13 #include "base/files/file_path.h"
     14 #include "base/logging.h"
     15 #include "base/posix/eintr_wrapper.h"
     16 
     17 namespace rlz_lib {
     18 
     19 bool RecursiveCrossProcessLock::TryGetCrossProcessLock(
     20     const base::FilePath& lock_filename) {
     21   bool just_got_lock = false;
     22 
     23   // Emulate a recursive mutex with a non-recursive one.
     24   if (pthread_mutex_trylock(&recursive_lock_) == EBUSY) {
     25     if (pthread_equal(pthread_self(), locking_thread_) == 0) {
     26       // Some other thread has the lock, wait for it.
     27       pthread_mutex_lock(&recursive_lock_);
     28       CHECK(locking_thread_ == 0);
     29       just_got_lock = true;
     30     }
     31   } else {
     32     just_got_lock = true;
     33   }
     34 
     35   locking_thread_ = pthread_self();
     36 
     37   // Try to acquire file lock.
     38   if (just_got_lock) {
     39     const int kMaxTimeoutMS = 5000;  // Matches Windows.
     40     const int kSleepPerTryMS = 200;
     41 
     42     CHECK(file_lock_ == -1);
     43     file_lock_ = open(lock_filename.value().c_str(), O_RDWR | O_CREAT, 0666);
     44     if (file_lock_ == -1) {
     45       perror("open");
     46       return false;
     47     }
     48 
     49     int flock_result = -1;
     50     int elapsed_ms = 0;
     51     while ((flock_result =
     52                HANDLE_EINTR(flock(file_lock_, LOCK_EX | LOCK_NB))) == -1 &&
     53            errno == EWOULDBLOCK &&
     54            elapsed_ms < kMaxTimeoutMS) {
     55       usleep(kSleepPerTryMS * 1000);
     56       elapsed_ms += kSleepPerTryMS;
     57     }
     58 
     59     if (flock_result == -1) {
     60       perror("flock");
     61       ignore_result(HANDLE_EINTR(close(file_lock_)));
     62       file_lock_ = -1;
     63       return false;
     64     }
     65     return true;
     66   } else {
     67     return file_lock_ != -1;
     68   }
     69 }
     70 
     71 void RecursiveCrossProcessLock::ReleaseLock() {
     72   if (file_lock_ != -1) {
     73     ignore_result(HANDLE_EINTR(flock(file_lock_, LOCK_UN)));
     74     ignore_result(HANDLE_EINTR(close(file_lock_)));
     75     file_lock_ = -1;
     76   }
     77 
     78   locking_thread_ = 0;
     79   pthread_mutex_unlock(&recursive_lock_);
     80 }
     81 
     82 }  // namespace rlz_lib
     83