From cd966c2ba6c3b3dbecd5c81627aa5a4ca59a40c9 Mon Sep 17 00:00:00 2001
From: Alexander Shalamov <alexander.shalamov@mapbox.com>
Date: Thu, 23 Apr 2020 16:04:37 +0300
Subject: Backport '[core] Use weak scheduler inside mailbox'

Backport: 40d42f339216e21e04b0ad2509de2fb4f6483103
---
 include/mbgl/actor/mailbox.hpp |  4 ++--
 src/mbgl/actor/mailbox.cpp     | 28 +++++++++++++++-------------
 2 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/include/mbgl/actor/mailbox.hpp b/include/mbgl/actor/mailbox.hpp
index 23c579917a..d2510e9270 100644
--- a/include/mbgl/actor/mailbox.hpp
+++ b/include/mbgl/actor/mailbox.hpp
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <mbgl/util/optional.hpp>
+#include <mapbox/std/weak.hpp>
 
 #include <memory>
 #include <mutex>
@@ -36,7 +36,7 @@ public:
     static void maybeReceive(std::weak_ptr<Mailbox>);
 
 private:
-    optional<Scheduler*> scheduler;
+    mapbox::base::WeakPtr<Scheduler> weakScheduler;
 
     std::recursive_mutex receivingMutex;
     std::mutex pushingMutex;
diff --git a/src/mbgl/actor/mailbox.cpp b/src/mbgl/actor/mailbox.cpp
index 8ee8dca114..e4e59efd77 100644
--- a/src/mbgl/actor/mailbox.cpp
+++ b/src/mbgl/actor/mailbox.cpp
@@ -9,26 +9,25 @@ namespace mbgl {
 Mailbox::Mailbox() {
 }
 
-Mailbox::Mailbox(Scheduler& scheduler_)
-    : scheduler(&scheduler_) {
-}
+Mailbox::Mailbox(Scheduler& scheduler_) : weakScheduler(scheduler_.makeWeakPtr()) {}
 
 void Mailbox::open(Scheduler& scheduler_) {
-    assert(!scheduler);
+    assert(!weakScheduler);
 
     // 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_;
+    weakScheduler = scheduler_.makeWeakPtr();
 
     if (closed) {
         return;
     }
     
     if (!queue.empty()) {
-        (*scheduler)->schedule(shared_from_this());
+        auto guard = weakScheduler.lock();
+        if (weakScheduler) weakScheduler->schedule(shared_from_this());
     }
 }
 
@@ -44,8 +43,9 @@ void Mailbox::close() {
     closed = true;
 }
 
-bool Mailbox::isOpen() const { return bool(scheduler); }
-
+bool Mailbox::isOpen() const {
+    return bool(weakScheduler);
+}
 
 void Mailbox::push(std::unique_ptr<Message> message) {
     std::lock_guard<std::mutex> pushingLock(pushingMutex);
@@ -57,15 +57,17 @@ 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) {
-        (*scheduler)->schedule(shared_from_this());
+    auto guard = weakScheduler.lock();
+    if (wasEmpty && weakScheduler) {
+        weakScheduler->schedule(shared_from_this());
     }
 }
 
 void Mailbox::receive() {
     std::lock_guard<std::recursive_mutex> receivingLock(receivingMutex);
-    
-    assert(scheduler);
+
+    auto guard = weakScheduler.lock();
+    assert(weakScheduler);
 
     if (closed) {
         return;
@@ -85,7 +87,7 @@ void Mailbox::receive() {
     (*message)();
 
     if (!wasEmpty) {
-        (*scheduler)->schedule(shared_from_this());
+        weakScheduler->schedule(shared_from_this());
     }
 }
 
-- 
cgit v1.2.1