Improve SharedMemory::Lock on Posix and reenable StatsTableTest.MultipleThreads

BUG=10611
TEST=NONE


Review URL: http://codereview.chromium.org/9463018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@123647 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 19 insertions, 13 deletions

diff --git a/base/metrics/stats_table_unittest.cc b/base/metrics/stats_table_unittest.cc
index 0a1c38bb..2755ace 100644
--- a/base/metrics/stats_table_unittest.cc
+++ b/base/metrics/stats_table_unittest.cc
@@ -106,8 +106,7 @@ void StatsTableThread::Run() {
 }
 
 // Create a few threads and have them poke on their counters.
-// Flaky, http://crbug.com/10611.
-TEST_F(StatsTableTest, DISABLED_MultipleThreads) {
+TEST_F(StatsTableTest, MultipleThreads) {
   // Create a stats table.
   const std::string kTableName = "MultipleThreadStatTable";
   const int kMaxThreads = 20;
diff --git a/base/shared_memory.h b/base/shared_memory.h
index 298baa6..a5744830 100644
--- a/base/shared_memory.h
+++ b/base/shared_memory.h
@@ -8,18 +8,22 @@
 
 #include "build/build_config.h"
 
+#include <string>
+
 #if defined(OS_POSIX)
 #include <stdio.h>
 #include <sys/types.h>
 #include <semaphore.h>
-#include "base/file_descriptor_posix.h"
 #endif
-#include <string>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/process.h"
 
+#if defined(OS_POSIX)
+#include "base/file_descriptor_posix.h"
+#endif
+
 class FilePath;
 
 namespace base {
@@ -201,14 +205,11 @@ class BASE_EXPORT SharedMemory {
   }
 
   // Locks the shared memory.
-  // This is a cross-process lock which may be recursively
-  // locked by the same thread.
-  // TODO(port):
-  // WARNING: on POSIX the lock only works across processes, not
-  // across threads.  2 threads in the same process can both grab the
-  // lock at the same time.  There are several solutions for this
-  // (futex, lockf+anon_semaphore) but none are both clean and common
-  // across Mac and Linux.
+  //
+  // WARNING: on POSIX the memory locking primitive only works across
+  // processes, not across threads.  The Lock method is not currently
+  // used in inner loops, so we protect against multiple threads in a
+  // critical section using a class global lock.
   void Lock();
 
 #if defined(OS_WIN)
diff --git a/base/shared_memory_posix.cc b/base/shared_memory_posix.cc
index 32a55e9..34403c4 100644
--- a/base/shared_memory_posix.cc
+++ b/base/shared_memory_posix.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -11,9 +11,11 @@
 #include <unistd.h>
 
 #include "base/file_util.h"
+#include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/threading/platform_thread.h"
 #include "base/safe_strerror_posix.h"
+#include "base/synchronization/lock.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/utf_string_conversions.h"
 
@@ -34,6 +36,8 @@ namespace {
 // namespaces, but who knows what's out there.
 const char kSemaphoreSuffix[] = "-sem";
 
+LazyInstance<Lock>::Leaky g_thread_lock_ = LAZY_INSTANCE_INITIALIZER;
+
 }
 
 SharedMemory::SharedMemory()
@@ -268,11 +272,13 @@ void SharedMemory::Close() {
 }
 
 void SharedMemory::Lock() {
+  g_thread_lock_.Get().Acquire();
   LockOrUnlockCommon(F_LOCK);
 }
 
 void SharedMemory::Unlock() {
   LockOrUnlockCommon(F_ULOCK);
+  g_thread_lock_.Get().Release();
 }
 
 #if !defined(OS_ANDROID)