[core] make thread pause/resume thread safe

include/mbgl/util/thread.hpp

@@ -96,9 +96,11 @@ class Thread : public Scheduler {
  // sent to a paused `Object` will be queued and only processed after
  // `resume()` is called.
  void pause() {
- MBGL_VERIFY_THREAD(tid);
+ std::unique_lock<std::mutex> lock(pauseMutex);
 
- assert(!paused);
+ if (paused) {
+ return;
+ }
 
  paused = std::make_unique<std::promise<void>>();
  resumed = std::make_unique<std::promise<void>>();
@@ -116,9 +118,11 @@ class Thread : public Scheduler {
 
  // Resumes the `Object` thread previously paused by `pause()`.
  void resume() {
- MBGL_VERIFY_THREAD(tid);
+ std::unique_lock<std::mutex> lock(pauseMutex);
 
- assert(paused);
+ if (!paused) {
+ return;
+ }
 
  resumed->set_value();
 

test/util/thread.test.cpp

@@ -7,6 +7,7 @@
 
 #include <atomic>
 #include <memory>
+#include <thread>
 
 using namespace mbgl;
 using namespace mbgl::util;
@@ -275,3 +276,35 @@ TEST(Thread, PauseResume) {
  thread.actor().invoke(&TestWorker::send, [&] { loop.stop(); });
  loop.run();
 }
+
+TEST(Thread, PauseResumeMultiThreaded) {
+ RunLoop loop;
+
+ // Thread to be paused
+ Thread<TestWorker> test("Test");
+
+ std::promise<void> thread1Complete;
+ auto future = thread1Complete.get_future();
+ std::thread thread1 {[&, promise = std::move(thread1Complete)]() mutable {
+ // Pause the thread
+ test.pause();
+ promise.set_value();
+ }};
+
+ // Wait for the test thread to be paused
+ future.wait();
+
+ std::thread thread2 {[&]() {
+ // Pause from this thread as well and resume
+ test.pause();
+ test.resume();
+ }};
+
+ // Queue a message at the end of test thread's queue.
+ test.actor().invoke(&TestWorker::send, [&] { loop.stop(); });
+ loop.run();
+
+ // Wait for threads
+ thread1.join();
+ thread2.join();
+}