lower thread priority of worker threads

gyp/platform-android.gypi

@@ -12,6 +12,7 @@
       'sources': [
         '../platform/android/log_android.cpp',
         '../platform/android/asset_root.cpp',
+        '../platform/default/thread.cpp',
         '../platform/default/string_stdlib.cpp',
         '../platform/default/image.cpp',
         '../platform/default/image_reader.cpp',

gyp/platform-ios.gypi

@@ -15,6 +15,7 @@
         '../platform/darwin/application_root.mm',
         '../platform/darwin/asset_root.mm',
         '../platform/darwin/image.mm',
+        '../platform/darwin/nsthread.mm',
         '../platform/darwin/reachability.m',
         '../include/mbgl/ios/MapboxGL.h',
         '../include/mbgl/ios/MGLMapboxEvents.h',

gyp/platform-linux.gypi

@@ -14,6 +14,7 @@
         '../platform/default/string_stdlib.cpp',
         '../platform/default/application_root.cpp',
         '../platform/default/asset_root.cpp',
+        '../platform/default/thread.cpp',
         '../platform/default/image.cpp',
         '../platform/default/image_reader.cpp',
         '../platform/default/png_reader.cpp',

gyp/platform-osx.gypi

@@ -15,6 +15,7 @@
         '../platform/darwin/application_root.mm',
         '../platform/darwin/asset_root.mm',
         '../platform/darwin/image.mm',
+        '../platform/darwin/nsthread.mm',
       ],
 
       'variables': {

include/mbgl/platform/platform.hpp

@@ -21,6 +21,9 @@ const std::string &applicationRoot();
 // Returns the path to the asset location.
 const std::string &assetRoot();
 
+// Makes the current thread low priority.
+void makeThreadLowPriority();
+
 // Shows an alpha image with the specified dimensions in a named window.
 void showDebugImage(std::string name, const char *data, size_t width, size_t height);
 

platform/darwin/nsthread.mm

@@ -0,0 +1,13 @@
+#import <Foundation/Foundation.h>
+
+#include <mbgl/platform/platform.hpp>
+
+namespace mbgl {
+namespace platform {
+
+void makeThreadLowPriority() {
+    [[NSThread currentThread] setThreadPriority:0.0];
+}
+
+}
+}

platform/default/sqlite_cache.cpp

@@ -62,7 +62,7 @@ std::string unifyMapboxURLs(const std::string &url) {
 using namespace mapbox::sqlite;
 
 SQLiteCache::SQLiteCache(const std::string& path_)
-    : thread(util::make_unique<util::Thread<Impl>>("SQLite Cache", path_)) {
+    : thread(util::make_unique<util::Thread<Impl>>("SQLite Cache", util::ThreadPriority::Low, path_)) {
 }
 
 SQLiteCache::~SQLiteCache() = default;

platform/default/thread.cpp

@@ -0,0 +1,11 @@
+#include <mbgl/platform/platform.hpp>
+
+namespace mbgl {
+namespace platform {
+
+void makeThreadLowPriority() {
+    // no-op
+}
+
+}
+}

src/mbgl/map/map.cpp

@@ -11,7 +11,7 @@ namespace mbgl {
 
 Map::Map(View& view, FileSource& fileSource, MapMode mode, bool startPaused)
     : data(util::make_unique<MapData>(view, mode)),
-      context(util::make_unique<util::Thread<MapContext>>("Map", view, fileSource, *data, startPaused))
+      context(util::make_unique<util::Thread<MapContext>>("Map", util::ThreadPriority::Regular, view, fileSource, *data, startPaused))
 {
     view.initialize(this);
 }

src/mbgl/storage/default_file_source.cpp

@@ -27,7 +27,7 @@ namespace algo = boost::algorithm;
 namespace mbgl {
 
 DefaultFileSource::DefaultFileSource(FileCache* cache, const std::string& root)
-    : thread(util::make_unique<util::Thread<Impl>>("FileSource", cache, root)) {
+    : thread(util::make_unique<util::Thread<Impl>>("FileSource", util::ThreadPriority::Low, cache, root)) {
 }
 
 DefaultFileSource::~DefaultFileSource() {

src/mbgl/util/thread.hpp

@@ -7,6 +7,7 @@
 #include <functional>
 
 #include <mbgl/util/run_loop.hpp>
+#include <mbgl/platform/platform.hpp>
 
 namespace {
 
@@ -34,11 +35,16 @@ namespace util {
 // Thread<> constructor blocks until the thread and the Object are fully created, so after the
 // object creation, it's safe to obtain the Object stored in this thread.
 
+enum class ThreadPriority : bool {
+    Regular,
+    Low,
+};
+
 template <class Object>
 class Thread {
 public:
     template <class... Args>
-    Thread(const std::string& name, Args&&... args);
+    Thread(const std::string& name, ThreadPriority priority, Args&&... args);
     ~Thread();
 
     // Invoke object->fn(args...) in the runloop thread.
@@ -97,7 +103,7 @@ private:
 
 template <class Object>
 template <class... Args>
-Thread<Object>::Thread(const std::string& name, Args&&... args) {
+Thread<Object>::Thread(const std::string& name, ThreadPriority priority, Args&&... args) {
     // Note: We're using std::tuple<> to store the arguments because GCC 4.9 has a bug
     // when expanding parameters packs captured in lambdas.
     std::tuple<Args...> params = std::forward_as_tuple(::std::forward<Args>(args)...);
@@ -109,6 +115,10 @@ Thread<Object>::Thread(const std::string& name, Args&&... args) {
         (void(name));
         #endif
 
+        if (priority == ThreadPriority::Low) {
+            platform::makeThreadLowPriority();
+        }
+
         constexpr auto seq = typename integer_sequence<sizeof...(Args)>::type();
         run(std::move(params), seq);
     });

src/mbgl/util/worker.cpp

@@ -1,4 +1,5 @@
 #include <mbgl/util/worker.hpp>
+#include <mbgl/platform/platform.hpp>
 
 #include <cassert>
 
@@ -15,7 +16,7 @@ public:
 
 Worker::Worker(std::size_t count) {
     for (std::size_t i = 0; i < count; i++) {
-        threads.emplace_back(util::make_unique<util::Thread<Impl>>("Worker"));
+        threads.emplace_back(util::make_unique<util::Thread<Impl>>("Worker", util::ThreadPriority::Low));
     }
 }