1 files changed, 15 insertions, 6 deletions
diff --git a/src/mbgl/actor/mailbox.cpp b/src/mbgl/actor/mailbox.cpp
index c117aa2605..20d9b25cad 100644
--- a/src/mbgl/actor/mailbox.cpp
+++ b/src/mbgl/actor/mailbox.cpp
@@ -6,6 +6,9 @@
 
 namespace mbgl {
 
+Mailbox::Mailbox() {
+}
+
 Mailbox::Mailbox(Scheduler& scheduler_)
     : scheduler(&scheduler_) {
 }
@@ -22,18 +25,22 @@ void Mailbox::close() {
     closed = true;
 }
 
-void Mailbox::setScheduler(Scheduler* scheduler_) {
+void Mailbox::start(Scheduler* scheduler_) {
+    assert(!scheduler);
+
+    // As with close(), block until neither receive() nor push() are in progress, and acquire the two
+    // mutexes in the same order.
     std::lock_guard<std::recursive_mutex> receivingLock(receivingMutex);
     std::lock_guard<std::mutex> pushingLock(pushingMutex);
     
     scheduler = scheduler_;
-    
+
     if (closed) {
         return;
     }
     
     if (!queue.empty()) {
-        scheduler->schedule(shared_from_this());
+        (*scheduler)->schedule(shared_from_this());
     }
 }
 
@@ -48,13 +55,15 @@ void Mailbox::push(std::unique_ptr<Message> message) {
     std::lock_guard<std::mutex> queueLock(queueMutex);
     bool wasEmpty = queue.empty();
     queue.push(std::move(message));
-    if (wasEmpty) {
-        scheduler->schedule(shared_from_this());
+    if (wasEmpty && scheduler) {
+        (*scheduler)->schedule(shared_from_this());
     }
 }
 
 void Mailbox::receive() {
     std::lock_guard<std::recursive_mutex> receivingLock(receivingMutex);
+    
+    assert(scheduler);
 
     if (closed) {
         return;
@@ -74,7 +83,7 @@ void Mailbox::receive() {
     (*message)();
 
     if (!wasEmpty) {
-        scheduler->schedule(shared_from_this());
+        (*scheduler)->schedule(shared_from_this());
     }
 }