[cros] RlzValueStore made protected by a cross-process lock and not persisted over browser lifetime…

rlz/lib/recursive_cross_process_lock_posix.cc

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "rlz/lib/recursive_cross_process_lock_posix.h"
+
+#include <sys/file.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "base/file_path.h"
+#include "base/logging.h"
+#include "base/posix/eintr_wrapper.h"
+
+namespace rlz_lib {
+
+bool RecursiveCrossProcessLock::TryGetCrossProcessLock(
+    const FilePath& lock_filename) {
+  bool just_got_lock = false;
+
+  // Emulate a recursive mutex with a non-recursive one.
+  if (pthread_mutex_trylock(&recursive_lock_) == EBUSY) {
+    if (pthread_equal(pthread_self(), locking_thread_) == 0) {
+      // Some other thread has the lock, wait for it.
+      pthread_mutex_lock(&recursive_lock_);
+      CHECK(locking_thread_ == 0);
+      just_got_lock = true;
+    }
+  } else {
+    just_got_lock = true;
+  }
+
+  locking_thread_ = pthread_self();
+
+  // Try to acquire file lock.
+  if (just_got_lock) {
+    const int kMaxTimeoutMS = 5000;  // Matches Windows.
+    const int kSleepPerTryMS = 200;
+
+    CHECK(file_lock_ == -1);
+    file_lock_ = open(lock_filename.value().c_str(), O_RDWR | O_CREAT, 0666);
+    if (file_lock_ == -1) {
+      perror("open");
+      return false;
+    }
+
+    int flock_result = -1;
+    int elapsed_ms = 0;
+    while ((flock_result =
+               HANDLE_EINTR(flock(file_lock_, LOCK_EX | LOCK_NB))) == -1 &&
+           errno == EWOULDBLOCK &&
+           elapsed_ms < kMaxTimeoutMS) {
+      usleep(kSleepPerTryMS * 1000);
+      elapsed_ms += kSleepPerTryMS;
+    }
+
+    if (flock_result == -1) {
+      perror("flock");
+      ignore_result(HANDLE_EINTR(close(file_lock_)));
+      file_lock_ = -1;
+      return false;
+    }
+    return true;
+  } else {
+    return file_lock_ != -1;

[Roger Tawa OOO till Jul 10th, 2012/11/26 19:16:51]

why not a DCHECK as well?  Under what normal situation would we already have the
mutex, but not the file lock?

[Ivan Korotkov, 2012/11/27 11:37:25]

I think the point of this line was that if the top-level Lock hasn't acquired
file lock, then all Locks down the stack will return false as well.

+  }
+}
+
+void RecursiveCrossProcessLock::ReleaseLock() {
+  if (file_lock_ != -1) {
+    ignore_result(HANDLE_EINTR(flock(file_lock_, LOCK_UN)));
+    ignore_result(HANDLE_EINTR(close(file_lock_)));
+    file_lock_ = -1;
+  }
+
+  locking_thread_ = 0;
+  pthread_mutex_unlock(&recursive_lock_);
+}
+
+}  // namespace rlz_lib