Android specific thread pool that keeps threads attached to JVM

include/mbgl/platform/thread.hpp

@@ -0,0 +1,13 @@
+#pragma once
+
+namespace mbgl {
+namespace platform {
+
+// Called when a thread is created
+void attachThread();
+
+// Called when a thread is destroyed
+void detachThread();
+
+} // namespace platform
+} // namespace mbgl

include/mbgl/util/thread.hpp

@@ -6,6 +6,7 @@
 #include <mbgl/util/platform.hpp>
 #include <mbgl/util/run_loop.hpp>
 #include <mbgl/util/util.hpp>
+#include <mbgl/platform/thread.hpp>
 
 #include <cassert>
 #include <future>
@@ -55,6 +56,7 @@ class Thread {
         ] () mutable {
             platform::setCurrentThreadName(name);
             platform::makeThreadLowPriority();
+            platform::attachThread();
 
             util::RunLoop loop_(util::RunLoop::Type::New);
             loop = &loop_;
@@ -67,6 +69,7 @@ class Thread {
             (void) establishedActor;
 
             loop = nullptr;
+            platform::detachThread();
         });
     }
 

platform/android/src/run_loop.cpp

@@ -81,9 +81,6 @@ class Alarm {
 };
 
 RunLoop::Impl::Impl(RunLoop* runLoop_, RunLoop::Type type) : runLoop(runLoop_) {
-    using namespace mbgl::android;
-    detach = attach_jni_thread(theJVM, &env, platform::getCurrentThreadName());
-
     loop = ALooper_prepare(0);
     assert(loop);
 
@@ -129,9 +126,6 @@ RunLoop::Impl::~Impl() {
     }
 
     ALooper_release(loop);
-
-    using namespace mbgl::android;
-    detach_jni_thread(theJVM, &env, detach);
 }
 
 void RunLoop::Impl::wake() {

platform/android/src/run_loop_impl.hpp

@@ -47,9 +47,6 @@ class RunLoop::Impl {
 
     int fds[2];
 
-    JNIEnv *env = nullptr;
-    bool detach = false;
-
     std::unique_ptr<Thread<Alarm>> alarm;
 
     std::mutex mutex;

platform/android/src/thread.cpp

@@ -1,14 +1,21 @@
 #include <mbgl/util/logging.hpp>
 #include <mbgl/util/platform.hpp>
+#include <mbgl/platform/thread.hpp>
 
 #include <sys/prctl.h>
 #include <sys/resource.h>
 
+#include <cassert>
+#include "jni.hpp"
+
 // Implementation based on Chromium's platform_thread_android.cc.
 
 namespace mbgl {
 namespace platform {
 
+thread_local static JNIEnv* env;
+thread_local static bool detach;
+
 std::string getCurrentThreadName() {
     char name[32] = "unknown";
 
@@ -33,5 +40,17 @@ void makeThreadLowPriority() {
     setpriority(PRIO_PROCESS, 0, 19);
 }
 
+void attachThread() {
+    using namespace android;
+    assert(env == nullptr);
+    detach = attach_jni_thread(theJVM, &env, platform::getCurrentThreadName());
+}
+
+void detachThread() {
+    using namespace android;
+    assert(env);
+    detach_jni_thread(theJVM, &env, detach);
+}
+
 } // namespace platform
 } // namespace mbgl

platform/darwin/src/nsthread.mm

@@ -1,6 +1,7 @@
 #import <Foundation/Foundation.h>
 
 #include <mbgl/util/platform.hpp>
+#include <mbgl/platform/thread.hpp>
 
 #include <pthread.h>
 
@@ -23,5 +24,11 @@ void makeThreadLowPriority() {
     [[NSThread currentThread] setThreadPriority:0.0];
 }
 
+void attachThread() {
+}
+
+void detachThread() {
+}
+
 }
 }

platform/default/src/mbgl/util/thread.cpp

@@ -1,4 +1,5 @@
 #include <mbgl/util/platform.hpp>
+#include <mbgl/platform/thread.hpp>
 #include <mbgl/util/logging.hpp>
 
 #include <string>
@@ -33,5 +34,11 @@ void makeThreadLowPriority() {
     }
 }
 
+void attachThread() {
+}
+
+void detachThread() {
+}
+
 } // namespace platform
 } // namespace mbgl

platform/qt/src/thread.cpp

@@ -1,4 +1,5 @@
 #include <mbgl/util/platform.hpp>
+#include <mbgl/platform/thread.hpp>
 
 #include <string>
 
@@ -15,5 +16,11 @@ void setCurrentThreadName(const std::string&) {
 void makeThreadLowPriority() {
 }
 
+void attachThread() {
+}
+
+void detachThread() {
+}
+
 } // namespace platform
 } // namespace mbgl

src/core-files.json

@@ -351,6 +351,7 @@
         "mbgl/math/minmax.hpp": "include/mbgl/math/minmax.hpp",
         "mbgl/math/wrap.hpp": "include/mbgl/math/wrap.hpp",
         "mbgl/platform/gl_functions.hpp": "include/mbgl/platform/gl_functions.hpp",
+        "mbgl/platform/thread.hpp": "include/mbgl/platform/thread.hpp",
         "mbgl/renderer/query.hpp": "include/mbgl/renderer/query.hpp",
         "mbgl/renderer/renderer.hpp": "include/mbgl/renderer/renderer.hpp",
         "mbgl/renderer/renderer_frontend.hpp": "include/mbgl/renderer/renderer_frontend.hpp",

src/mbgl/util/thread_pool.cpp

@@ -2,6 +2,7 @@
 
 #include <mbgl/util/platform.hpp>
 #include <mbgl/util/string.hpp>
+#include <mbgl/platform/thread.hpp>
 
 namespace mbgl {
 
@@ -11,6 +12,7 @@ ThreadPool::ThreadPool(std::size_t count) {
     for (std::size_t i = 0; i < count; ++i) {
         threads.emplace_back([this, i]() {
             platform::setCurrentThreadName(std::string{ "Worker " } + util::toString(i + 1));
+            platform::attachThread();
 
             while (true) {
                 std::unique_lock<std::mutex> lock(mutex);
@@ -20,6 +22,7 @@ ThreadPool::ThreadPool(std::size_t count) {
                 });
 
                 if (terminate) {
+                    platform::detachThread();
                     return;
                 }