Add multi_process_lock to base

Platform abstraction for a shared lock between processes. The process
that owns the lock will release it on exit even if exit is due
to a crash.

For cloud-print and remoting we want to be able to have a singleton service-process that can run independently of the browser process. This service process will communicate with the browser process via the standard IAC channels, but we want to have a way of signaling to other processes that a) there is a service-process running and b) that it is in a state where it is ready to be communicated with. The multi_process_lock class is intended to work as a simple flag that can be queried from multiple processes. If the service-process should crash, we would like the flag to be cleared automatically so that there is never confusion about the state of the service-process.

Other approaches considered for some Unix/Mac:
- Standard unix domain sockets depend on the file system and don't clean up properly in the case of a crash.
- Shared memory on unix depend on the file system and don't clean up properly in the case of a crash.
- System V semaphores on unix again depend on the file system.
- named_mach_ports on Mac OS. Bootstrap_register_name has been deprecated on 10.6, so we are doing essentially the same thing using CFMessagePort.

On Windows it is implemented as an event.
On Mac it is implemented using a CFMessagePort name.
On Linux it is implement using an abstract name port socket.

TEST=none
BUG=none

Review URL: http://codereview.chromium.org/4721001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@66323 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 54 insertions, 0 deletions

diff --git a/chrome/common/multi_process_lock_mac.cc b/chrome/common/multi_process_lock_mac.cc
new file mode 100644
index 0000000..9a16d71
--- /dev/null
+++ b/chrome/common/multi_process_lock_mac.cc
@@ -0,0 +1,54 @@
+// Copyright (c) 2010 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 "chrome/common/multi_process_lock.h"
+
+#include "base/logging.h"
+#include "base/mac/scoped_cftyperef.h"
+#include "base/sys_string_conversions.h"
+
+class MultiProcessLockMac : public MultiProcessLock {
+ public:
+  explicit MultiProcessLockMac(const std::string& name) : name_(name) { }
+
+  virtual ~MultiProcessLockMac() {
+    if (port_ != NULL) {
+      Unlock();
+    }
+  }
+
+  virtual bool TryLock() {
+    if (port_ != NULL) {
+      DLOG(ERROR) << "MultiProcessLock is already locked - " << name_;
+      return true;
+    }
+
+    if (name_.length() > MULTI_PROCESS_LOCK_NAME_MAX_LEN) {
+      LOG(ERROR) << "Socket name too long - " << name_;
+      return false;
+    }
+
+    CFStringRef cf_name(base::SysUTF8ToCFStringRef(name_));
+    base::mac::ScopedCFTypeRef<CFStringRef> scoped_cf_name(cf_name);
+    port_.reset(CFMessagePortCreateLocal(NULL, cf_name, NULL, NULL, NULL));
+    return port_ != NULL;
+  }
+
+  virtual void Unlock() {
+    if (port_ == NULL) {
+      DLOG(ERROR) << "Over-unlocked MultiProcessLock - " << name_;
+      return;
+    }
+    port_.reset();
+  }
+
+ private:
+  std::string name_;
+  base::mac::ScopedCFTypeRef<CFMessagePortRef> port_;
+  DISALLOW_COPY_AND_ASSIGN(MultiProcessLockMac);
+};
+
+MultiProcessLock* MultiProcessLock::Create(const std::string &name) {
+  return new MultiProcessLockMac(name);
+}