Asynchronous GeometryTile deletion (#2051)

Co-authored-by: Tim Sylvester <tim@wetdogweather.com>

platform/android/src/run_loop.cpp

@@ -1,11 +1,13 @@
 #include "run_loop_impl.hpp"
 
-#include <mbgl/util/platform.hpp>
-#include <mbgl/util/thread_local.hpp>
-#include <mbgl/util/thread.hpp>
-#include <mbgl/util/timer.hpp>
 #include <mbgl/actor/scheduler.hpp>
 #include <mbgl/util/event.hpp>
+#include <mbgl/util/logging.hpp>
+#include <mbgl/util/monotonic_timer.hpp>
+#include <mbgl/util/platform.hpp>
+#include <mbgl/util/thread.hpp>
+#include <mbgl/util/thread_local.hpp>
+#include <mbgl/util/timer.hpp>
 
 #include <android/looper.h>
 
@@ -18,7 +20,6 @@
 
 #include <fcntl.h>
 #include <unistd.h>
-#include <mbgl/util/logging.hpp>
 
 #define PIPE_OUT 0
 #define PIPE_IN 1
@@ -167,6 +168,9 @@ void RunLoop::Impl::addRunnable(Runnable* runnable) {
 void RunLoop::Impl::removeRunnable(Runnable* runnable) {
     std::lock_guard<std::mutex> lock(mutex);
     runnables.remove(runnable);
+    if (runnables.empty()) {
+        cvEmpty.notify_all();
+    }
 }
 
 Milliseconds RunLoop::Impl::processRunnables() {
@@ -196,6 +200,10 @@ Milliseconds RunLoop::Impl::processRunnables() {
         runnable->runTask();
     }
 
+    if (runnables.empty()) {
+        cvEmpty.notify_all();
+    }
+
     if (runnables.empty() || nextDue == TimePoint::max()) {
         return Milliseconds(-1);
     }
@@ -208,6 +216,25 @@ Milliseconds RunLoop::Impl::processRunnables() {
     return timeout;
 }
 
+std::size_t RunLoop::Impl::waitForEmpty(Milliseconds timeout) {
+    const auto startTime = mbgl::util::MonotonicTimer::now();
+    while (true) {
+        std::size_t remaining;
+        {
+            std::lock_guard<std::mutex> lock(mutex);
+            remaining = runnables.size();
+        }
+
+        const auto elapsed = mbgl::util::MonotonicTimer::now() - startTime;
+        const auto elapsedMillis = std::chrono::duration_cast<Milliseconds>(elapsed);
+        if (remaining == 0 || (Milliseconds::zero() < timeout && timeout <= elapsedMillis)) {
+            return remaining;
+        }
+
+        runLoop->runOnce();
+    }
+}
+
 RunLoop* RunLoop::Get() {
     assert(static_cast<RunLoop*>(Scheduler::GetCurrent()));
     return static_cast<RunLoop*>(Scheduler::GetCurrent());
@@ -230,6 +257,10 @@ void RunLoop::wake() {
     impl->wake();
 }
 
+std::size_t RunLoop::waitForEmpty(std::chrono::milliseconds timeout) {
+    return impl->waitForEmpty(timeout);
+}
+
 void RunLoop::run() {
     MBGL_VERIFY_THREAD(tid);