Add multi_process_lock to chrome/common

chrome/common/multi_process_lock_mac.cc

+// 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), count_(0) { }

[Mark Mentovai, 2010/11/11 23:45:24]

Will this be accessed from multiple threads?

If so (or if this is multithreading-safe on other platforms and you want the Mac
to match), fix up.

If not, use preincrement/decrement when you operate on count, because I think
that’s what folks are used to seeing.

[dmac, 2010/11/12 00:36:26]

Good point regarding multi threads. I got rid of the recursion as I don't need
it currently, and there's no point in over designing right now. If somebody
needs it later they can do the wrapper class as you suggested.

+

[Mark Mentovai, 2010/11/11 23:45:24]

OK, I just looked at your implementation on other platforms and see that it’s
the same deal.

Maybe you’d be better off putting all of that “count” logic in some outer-outer
platform-dependent class, like RecursiveMultiProcessLock, that wraps
MultiProcessLock?

[dmac, 2010/11/12 00:36:26]

Done.

+  virtual ~MultiProcessLockMac() {
+    if (count_ > 0) {
+      Unlock();
+    }
+  }
+
+  virtual bool TryLock() {
+    if (count_ > 0) {
+      count_ += 1;
+      return true;
+    }
+    CFStringRef cf_name(base::SysUTF8ToCFStringRef(name_));
+    base::mac::ScopedCFTypeRef<CFStringRef> scoped_cf_name(cf_name);
+    port_.reset(CFMessagePortCreateLocal(NULL, cf_name, NULL, NULL, NULL));
+    if (port_ != NULL) {
+      count_ = 1;
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  virtual void Unlock() {
+    if (count_ == 0) {
+      DLOG(ERROR) << "Over unlocked MultiProcessLock " << name_;

[Mark Mentovai, 2010/11/11 23:45:24]

I’d hyphenate this dude.

[dmac, 2010/11/12 00:36:26]

Done.

+      return;
+    }
+    count_ -= 1;
+    if (count_ == 0) {
+      port_.reset();
+    }
+  }
+
+ private:
+  std::string name_;
+  int count_;
+  base::mac::ScopedCFTypeRef<CFMessagePortRef> port_;

[Mark Mentovai, 2010/11/11 23:45:24]

Improve the struct packing. Put port_ before count_.

[dmac, 2010/11/12 00:36:26]

Done.

+  DISALLOW_COPY_AND_ASSIGN(MultiProcessLockMac);
+};
+
+MultiProcessLock* MultiProcessLock::Create(const std::string &name) {
+  return new MultiProcessLockMac(name);
+}