rlz/lib/recursive_cross_process_lock_posix.cc

   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