Guard startup_data_ to ensure it is set.

On SMP systems, instructions can be reordered such that the new thread executes
before startup_data_ has been written.  Use a mutex to ensure instruction order
and to force startup_data_ to be flushed.  This fixes spurious crashes when
starting the browser.

Bug: 3291265
Change-Id: Idb29cda6e03d01d42781284d5a9545486ee92bc8

2 files changed, 30 insertions, 0 deletions

diff --git a/base/thread.cc b/base/thread.cc
index 41d78f0..e397be6 100644
--- a/base/thread.cc
+++ b/base/thread.cc
@@ -81,7 +81,16 @@ bool Thread::StartWithOptions(const Options& options) {
   SetThreadWasQuitProperly(false);
 
   StartupData startup_data(options);
+#ifdef ANDROID
+  {
+    // Use a lock to issue a cpu barrier and force the new thread to load
+    // startup_data_.
+    AutoLock lock(startup_data_lock_);
+    startup_data_ = &startup_data;
+  }
+#else
   startup_data_ = &startup_data;
+#endif
 
   if (!PlatformThread::Create(options.stack_size, this, &thread_)) {
     DLOG(ERROR) << "failed to create thread";
@@ -142,8 +151,19 @@ void Thread::Run(MessageLoop* message_loop) {
 
 void Thread::ThreadMain() {
   {
+#ifdef ANDROID
+    StartupData* startup_data = NULL;
+    {
+      // Use a lock to ensure startup_data_ has been written.
+      AutoLock lock(startup_data_lock_);
+      startup_data = startup_data_;
+    }
+    // The message loop for this thread.
+    MessageLoop message_loop(startup_data->options.message_loop_type);
+#else
     // The message loop for this thread.
     MessageLoop message_loop(startup_data_->options.message_loop_type);
+#endif
 
     // Complete the initialization of our Thread object.
     thread_id_ = PlatformThread::CurrentId();
@@ -157,7 +177,11 @@ void Thread::ThreadMain() {
     // Let's do this before signaling we are started.
     Init();
 
+#ifdef ANDROID
+    startup_data->event.Signal();
+#else
     startup_data_->event.Signal();
+#endif
     // startup_data_ can't be touched anymore since the starting thread is now
     // unlocked.
 
diff --git a/base/thread.h b/base/thread.h
index 572eb8a..870a985 100644
--- a/base/thread.h
+++ b/base/thread.h
@@ -8,6 +8,9 @@
 
 #include <string>
 
+#ifdef ANDROID
+#include "base/lock.h"
+#endif
 #include "base/message_loop.h"
 #include "base/message_loop_proxy.h"
 #include "base/platform_thread.h"
@@ -165,6 +168,9 @@ class Thread : PlatformThread::Delegate {
   bool stopping_;
 
   // Used to pass data to ThreadMain.
+#ifdef ANDROID
+  Lock startup_data_lock_;  // protects startup_data_
+#endif
   struct StartupData;
   StartupData* startup_data_;