Make mojo::RunLoop just use pthreads.

mojo/public/cpp/utility/lib/run_loop.cc

 // Copyright 2014 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 "mojo/public/cpp/utility/run_loop.h"
 
 #include <assert.h>
+#include <pthread.h>
 
 #include <algorithm>
 #include <vector>
 
+#include "mojo/public/c/system/macros.h"
 #include "mojo/public/cpp/system/time.h"
 #include "mojo/public/cpp/system/wait.h"
-#include "mojo/public/cpp/utility/lib/thread_local.h"
 #include "mojo/public/cpp/utility/run_loop_handler.h"
 
 namespace mojo {
 namespace {
 
-internal::ThreadLocalPointer<RunLoop> current_run_loop;
+const MojoTimeTicks kInvalidTimeTicks = static_cast<MojoTimeTicks>(0);
 
-const MojoTimeTicks kInvalidTimeTicks = static_cast<MojoTimeTicks>(0);
+pthread_key_t g_current_run_loop_key;
+
+// Ensures that the "current run loop" functionality is available (i.e., that we
+// have a TLS slot).
+void EnsureCurrentRunLoopInitialized() {
+  static pthread_once_t current_run_loop_key_once = PTHREAD_ONCE_INIT;
+  int error = pthread_once(&current_run_loop_key_once, []() {
+    int error = pthread_key_create(&g_current_run_loop_key, nullptr);

[vardhan, 2016/05/19 21:37:35]

does it make sense to provide a destructor to pthread_key_create() that tears
down the current runloop?

i guess the current thread's RunLoop will always be destroyed before the thread
is destroyed (unless RunLoop is dynamically allocated or something and
mismanaged or something).

+    MOJO_ALLOW_UNUSED_LOCAL(error);
+    assert(!error);
+  });
+  MOJO_ALLOW_UNUSED_LOCAL(error);
+  assert(!error);
+}
+
+void SetCurrentRunLoop(RunLoop* run_loop) {
+  EnsureCurrentRunLoopInitialized();
+
+  int error = pthread_setspecific(g_current_run_loop_key, run_loop);
+  MOJO_ALLOW_UNUSED_LOCAL(error);
+  assert(!error);
+}
 
 // State needed for one iteration of WaitMany().
 struct WaitState {
   std::vector<Handle> handles;
   std::vector<MojoHandleSignals> handle_signals;
   MojoDeadline deadline = MOJO_DEADLINE_INDEFINITE;
 };
 
 }  // namespace
 
 struct RunLoop::RunState {
   bool should_quit = false;
   WaitState wait_state;
 };
 
 RunLoop::RunLoop()
     : run_state_(nullptr), next_handler_id_(0), next_sequence_number_(0) {
   assert(!current());
-  current_run_loop.Set(this);
+  SetCurrentRunLoop(this);
 }
 
 RunLoop::~RunLoop() {
   assert(current() == this);
   NotifyHandlers(MOJO_RESULT_ABORTED, IGNORE_DEADLINE);
-  current_run_loop.Set(nullptr);
-}
-
-// static
-void RunLoop::SetUp() {
-  current_run_loop.Allocate();
-}
-
-// static
-void RunLoop::TearDown() {
-  assert(!current());
-  current_run_loop.Free();
+  SetCurrentRunLoop(nullptr);
 }
 
 // static
 RunLoop* RunLoop::current() {
-  return current_run_loop.Get();
+  EnsureCurrentRunLoopInitialized();
+  return static_cast<RunLoop*>(pthread_getspecific(g_current_run_loop_key));
 }
 
 void RunLoop::AddHandler(RunLoopHandler* handler,
                          const Handle& handle,
                          MojoHandleSignals handle_signals,
                          MojoDeadline deadline) {
   assert(current() == this);
   assert(handler);
   assert(handle.is_valid());
   // Assume it's an error if someone tries to reregister an existing handle.
@@ skipping 192 matching lines @@
     // std::priority_queue<> puts the least element at the end of the queue. We
     // want the soonest eligible task to be at the head of the queue, so
     // run_times further in the future are considered lesser.
     return run_time > other.run_time;
   }
 
   return sequence_number > other.sequence_number;
 }
 
 }  // namespace mojo