use separate workers for tile parsing to avoid blocking the threadpool for other libuv actions

5 files changed, 59 insertions, 8 deletions

diff --git a/src/map/map.cpp b/src/map/map.cpp
index ecf4eb2837..93e1bea536 100644
--- a/src/map/map.cpp
+++ b/src/map/map.cpp
@@ -60,6 +60,13 @@ Map::~Map() {
     }
 }
 
+uv::worker &Map::getWorker() {
+    if (!workers) {
+        workers = std::make_unique<uv::worker>(**loop, 4, "Tile Worker");
+    }
+    return *workers;
+}
+
 void Map::start() {
     assert(uv_thread_self() == main_thread);
     assert(!async);
@@ -198,6 +205,7 @@ void Map::terminate(uv_async_t *async) {
     map->glyphStore.reset();
     map->fileSource.reset();
     map->style.reset();
+    map->workers.reset();
     map->activeSources.clear();
 
     uv_close((uv_handle_t *)map->async_cleanup.get(), nullptr);
diff --git a/src/map/tile_data.cpp b/src/map/tile_data.cpp
index 2a0e96cad6..ecb05d5b26 100644
--- a/src/map/tile_data.cpp
+++ b/src/map/tile_data.cpp
@@ -87,7 +87,7 @@ void TileData::reparse() {
     // We're creating a new work request. The work request deletes itself after it executed
     // the after work handler
     new uv::work<util::ptr<TileData>>(
-        map.getLoop(),
+        map.getWorker(),
         [](util::ptr<TileData> &tile) {
             tile->parse();
         },
diff --git a/src/storage/sqlite_store.cpp b/src/storage/sqlite_store.cpp
index baa599eef9..d44520a95e 100644
--- a/src/storage/sqlite_store.cpp
+++ b/src/storage/sqlite_store.cpp
@@ -32,7 +32,7 @@ SQLiteStore::SQLiteStore(uv_loop_t *loop, const std::string &path)
       db(std::make_shared<Database>(path.c_str(), ReadWrite | Create)) {
     createSchema();
     worker = new uv_worker_t;
-    uv_worker_init_named(worker, loop, "SQLite");
+    uv_worker_init(worker, loop, 1, "SQLite");
 }
 
 SQLiteStore::~SQLiteStore() {
diff --git a/src/util/uv-channel.c b/src/util/uv-channel.c
index 3d0483fd70..2936b01c53 100644
--- a/src/util/uv-channel.c
+++ b/src/util/uv-channel.c
@@ -49,7 +49,21 @@ void *uv_chan_receive(uv_chan_t *chan) {
     return data;
 }
 
+void uv_chan_clear(uv_chan_t *chan) {
+    uv_mutex_lock(&chan->mutex);
+    uv__chan_item_t *item = NULL;
+    QUEUE *head = NULL;
+    while (!QUEUE_EMPTY(&chan->q)) {
+        head = QUEUE_HEAD(&chan->q);
+        item = QUEUE_DATA(head, uv__chan_item_t, active_queue);
+        QUEUE_REMOVE(head);
+        free(item);
+    }
+    uv_mutex_unlock(&chan->mutex);
+}
+
 void uv_chan_destroy(uv_chan_t *chan) {
+    uv_chan_clear(chan);
     uv_cond_destroy(&chan->cond);
     uv_mutex_destroy(&chan->mutex);
 }
diff --git a/src/util/uv-worker.c b/src/util/uv-worker.c
index d0e2550b73..c47b0ffed2 100644
--- a/src/util/uv-worker.c
+++ b/src/util/uv-worker.c
@@ -1,5 +1,6 @@
 #include <mbgl/util/uv-worker.h>
 #include <mbgl/util/uv-messenger.h>
+#include <mbgl/util/queue.h>
 
 #include <stdio.h>
 
@@ -10,6 +11,12 @@ struct uv__worker_item_s {
     uv_worker_after_cb after_work_cb;
 };
 
+typedef struct uv__work_thread_s uv__work_thread_t;
+struct uv__work_thread_s {
+    uv_thread_t thread;
+    void *queue[2];
+};
+
 void uv__worker_after(void *ptr) {
     uv__worker_item_t *item = (uv__worker_item_t *)ptr;
     item->after_work_cb(item->data);
@@ -30,20 +37,29 @@ void uv__worker_thread_loop(void *ptr) {
         item->work_cb(item->data);
         uv_messenger_send(worker->msgr, item);
     }
-}
 
-int uv_worker_init(uv_worker_t *worker, uv_loop_t *loop) {
-    return uv_worker_init_named(worker, loop, NULL);
+    // Make sure to close all other workers too.
+    uv_chan_send(&worker->chan, NULL);
 }
 
-int uv_worker_init_named(uv_worker_t *worker, uv_loop_t *loop, const char *name) {
+int uv_worker_init(uv_worker_t *worker, uv_loop_t *loop, int count, const char *name) {
     worker->name = name;
     worker->msgr = malloc(sizeof(uv_messenger_t));
     int ret = uv_messenger_init(loop, worker->msgr, uv__worker_after);
     if (ret < 0) return ret;
     ret = uv_chan_init(&worker->chan);
     if (ret < 0) return ret;
-    return uv_thread_create(&worker->thread, uv__worker_thread_loop, worker);
+
+    // Initialize worker threads.
+    QUEUE_INIT(&worker->threads);
+    for (int i = 0; i < count; i++) {
+        uv__work_thread_t *work_thread = malloc(sizeof(uv__work_thread_t));
+        ret = uv_thread_create(&work_thread->thread, uv__worker_thread_loop, worker);
+        if (ret < 0) return ret;
+        QUEUE_INSERT_TAIL(&worker->threads, &work_thread->queue);
+    }
+
+    return 0;
 }
 
 void uv_worker_send(uv_worker_t *worker, void *data, uv_worker_cb work_cb,
@@ -55,8 +71,21 @@ void uv_worker_send(uv_worker_t *worker, void *data, uv_worker_cb work_cb,
     uv_chan_send(&worker->chan, item);
 }
 
+void uv_worker_join_all(uv_worker_t *worker) {
+    QUEUE *head = NULL;
+    uv__work_thread_t *item = NULL;
+    while (!QUEUE_EMPTY(&worker->threads)) {
+        head = QUEUE_HEAD(&worker->threads);
+        item = QUEUE_DATA(head, uv__work_thread_t, queue);
+        QUEUE_REMOVE(head);
+        uv_thread_join(&item->thread);
+        free(item);
+    }
+}
+
 void uv_worker_close(uv_worker_t *worker) {
     uv_chan_send(&worker->chan, NULL);
-    uv_thread_join(&worker->thread);
+    uv_worker_join_all(worker);
+    uv_chan_destroy(&worker->chan);
     uv_messenger_stop(worker->msgr);
 }