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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 <errno.h>
      8 #include <fcntl.h>
      9 #include <sys/file.h>
     10 #include <sys/stat.h>
     11 #include <sys/types.h>
     12 #include <unistd.h>
     13 
     14 #include "base/files/file_path.h"
     15 #include "base/logging.h"
     16 #include "base/posix/eintr_wrapper.h"
     17 
     18 namespace rlz_lib {
     19 
     20 bool RecursiveCrossProcessLock::TryGetCrossProcessLock(
     21     const base::FilePath& lock_filename) {
     22   bool just_got_lock = false;
     23 
     24   // Emulate a recursive mutex with a non-recursive one.
     25   if (pthread_mutex_trylock(&recursive_lock_) == EBUSY) {
     26     if (pthread_equal(pthread_self(), locking_thread_) == 0) {
     27       // Some other thread has the lock, wait for it.
     28       pthread_mutex_lock(&recursive_lock_);
     29       CHECK(locking_thread_ == 0);
     30       just_got_lock = true;
     31     }
     32   } else {
     33     just_got_lock = true;
     34   }
     35 
     36   locking_thread_ = pthread_self();
     37 
     38   // Try to acquire file lock.
     39   if (just_got_lock) {
     40     const int kMaxTimeoutMS = 5000;  // Matches Windows.
     41     const int kSleepPerTryMS = 200;
     42 
     43     CHECK(file_lock_ == -1);
     44     file_lock_ = open(lock_filename.value().c_str(), O_RDWR | O_CREAT, 0666);
     45     if (file_lock_ == -1) {
     46       perror("open");
     47       return false;
     48     }
     49 
     50     int flock_result = -1;
     51     int elapsed_ms = 0;
     52     while ((flock_result =
     53                HANDLE_EINTR(flock(file_lock_, LOCK_EX | LOCK_NB))) == -1 &&
     54            errno == EWOULDBLOCK &&
     55            elapsed_ms < kMaxTimeoutMS) {
     56       usleep(kSleepPerTryMS * 1000);
     57       elapsed_ms += kSleepPerTryMS;
     58     }
     59 
     60     if (flock_result == -1) {
     61       perror("flock");
     62       close(file_lock_);
     63       file_lock_ = -1;
     64       return false;
     65     }
     66     return true;
     67   } else {
     68     return file_lock_ != -1;
     69   }
     70 }
     71 
     72 void RecursiveCrossProcessLock::ReleaseLock() {
     73   if (file_lock_ != -1) {
     74     ignore_result(HANDLE_EINTR(flock(file_lock_, LOCK_UN)));
     75     close(file_lock_);
     76     file_lock_ = -1;
     77   }
     78 
     79   locking_thread_ = 0;
     80   pthread_mutex_unlock(&recursive_lock_);
     81 }
     82 
     83 }  // namespace rlz_lib
     84