From 034551f1519491110b83f74662af7d4c0c509104 Mon Sep 17 00:00:00 2001
From: Ivo van Dongen <info@ivovandongen.nl>
Date: Fri, 21 Jul 2017 15:51:34 +0300
Subject: [core] make thread pause/resume thread safe

---
 include/mbgl/util/thread.hpp | 12 ++++++++----
 test/util/thread.test.cpp    | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/include/mbgl/util/thread.hpp b/include/mbgl/util/thread.hpp
index 572f46080e..06254569a9 100644
--- a/include/mbgl/util/thread.hpp
+++ b/include/mbgl/util/thread.hpp
@@ -96,9 +96,11 @@ public:
     // 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 @@ public:
 
     // 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();
 
diff --git a/test/util/thread.test.cpp b/test/util/thread.test.cpp
index 76fb5ce3f0..228e463d9e 100644
--- a/test/util/thread.test.cpp
+++ b/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();
+}
-- 
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