2 files changed, 170 insertions, 0 deletions

diff --git a/include/block/thread-pool.h b/include/block/thread-pool.h
index 6f27eb085b..dd48cf07e8 100644
--- a/include/block/thread-pool.h
+++ b/include/block/thread-pool.h
@@ -38,5 +38,56 @@ BlockAIOCB *thread_pool_submit_aio(ThreadPoolFunc *func, void *arg,
 int coroutine_fn thread_pool_submit_co(ThreadPoolFunc *func, void *arg);
 void thread_pool_update_params(ThreadPoolAio *pool, struct AioContext *ctx);
 
+/* ------------------------------------------- */
+/* Generic thread pool types and methods below */
+typedef struct ThreadPool ThreadPool;
+
+/* Create a new thread pool. Never returns NULL. */
+ThreadPool *thread_pool_new(void);
+
+/*
+ * Free the thread pool.
+ * Waits for all the previously submitted work to complete before performing
+ * the actual freeing operation.
+ */
+void thread_pool_free(ThreadPool *pool);
+
+/*
+ * Submit a new work (task) for the pool.
+ *
+ * @opaque_destroy is an optional GDestroyNotify for the @opaque argument
+ * to the work function at @func.
+ */
+void thread_pool_submit(ThreadPool *pool, ThreadPoolFunc *func,
+                        void *opaque, GDestroyNotify opaque_destroy);
+
+/*
+ * Submit a new work (task) for the pool, making sure it starts getting
+ * processed immediately, launching a new thread for it if necessary.
+ *
+ * @opaque_destroy is an optional GDestroyNotify for the @opaque argument
+ * to the work function at @func.
+ */
+void thread_pool_submit_immediate(ThreadPool *pool, ThreadPoolFunc *func,
+                                  void *opaque, GDestroyNotify opaque_destroy);
+
+/*
+ * Wait for all previously submitted work to complete before returning.
+ *
+ * Can be used as a barrier between two sets of tasks executed on a thread
+ * pool without destroying it or in a performance sensitive path where the
+ * caller just wants to wait for all tasks to complete while deferring the
+ * pool free operation for later, less performance sensitive time.
+ */
+void thread_pool_wait(ThreadPool *pool);
+
+/* Set the maximum number of threads in the pool. */
+bool thread_pool_set_max_threads(ThreadPool *pool, int max_threads);
+
+/*
+ * Adjust the maximum number of threads in the pool to give each task its
+ * own thread (exactly one thread per task).
+ */
+bool thread_pool_adjust_max_threads_to_work(ThreadPool *pool);
 
 #endif
diff --git a/util/thread-pool.c b/util/thread-pool.c
index 908194dc07..d2ead6b728 100644
--- a/util/thread-pool.c
+++ b/util/thread-pool.c
@@ -374,3 +374,122 @@ void thread_pool_free_aio(ThreadPoolAio *pool)
     qemu_mutex_destroy(&pool->lock);
     g_free(pool);
 }
+
+struct ThreadPool {
+    GThreadPool *t;
+    size_t cur_work;
+    QemuMutex cur_work_lock;
+    QemuCond all_finished_cond;
+};
+
+typedef struct {
+    ThreadPoolFunc *func;
+    void *opaque;
+    GDestroyNotify opaque_destroy;
+} ThreadPoolElement;
+
+static void thread_pool_func(gpointer data, gpointer user_data)
+{
+    ThreadPool *pool = user_data;
+    g_autofree ThreadPoolElement *el = data;
+
+    el->func(el->opaque);
+
+    if (el->opaque_destroy) {
+        el->opaque_destroy(el->opaque);
+    }
+
+    QEMU_LOCK_GUARD(&pool->cur_work_lock);
+
+    assert(pool->cur_work > 0);
+    pool->cur_work--;
+
+    if (pool->cur_work == 0) {
+        qemu_cond_signal(&pool->all_finished_cond);
+    }
+}
+
+ThreadPool *thread_pool_new(void)
+{
+    ThreadPool *pool = g_new(ThreadPool, 1);
+
+    pool->cur_work = 0;
+    qemu_mutex_init(&pool->cur_work_lock);
+    qemu_cond_init(&pool->all_finished_cond);
+
+    pool->t = g_thread_pool_new(thread_pool_func, pool, 0, TRUE, NULL);
+    /*
+     * g_thread_pool_new() can only return errors if initial thread(s)
+     * creation fails but we ask for 0 initial threads above.
+     */
+    assert(pool->t);
+
+    return pool;
+}
+
+void thread_pool_free(ThreadPool *pool)
+{
+    /*
+     * With _wait = TRUE this effectively waits for all
+     * previously submitted work to complete first.
+     */
+    g_thread_pool_free(pool->t, FALSE, TRUE);
+
+    qemu_cond_destroy(&pool->all_finished_cond);
+    qemu_mutex_destroy(&pool->cur_work_lock);
+
+    g_free(pool);
+}
+
+void thread_pool_submit(ThreadPool *pool, ThreadPoolFunc *func,
+                        void *opaque, GDestroyNotify opaque_destroy)
+{
+    ThreadPoolElement *el = g_new(ThreadPoolElement, 1);
+
+    el->func = func;
+    el->opaque = opaque;
+    el->opaque_destroy = opaque_destroy;
+
+    WITH_QEMU_LOCK_GUARD(&pool->cur_work_lock) {
+        pool->cur_work++;
+    }
+
+    /*
+     * Ignore the return value since this function can only return errors
+     * if creation of an additional thread fails but even in this case the
+     * provided work is still getting queued (just for the existing threads).
+     */
+    g_thread_pool_push(pool->t, el, NULL);
+}
+
+void thread_pool_submit_immediate(ThreadPool *pool, ThreadPoolFunc *func,
+                                  void *opaque, GDestroyNotify opaque_destroy)
+{
+    thread_pool_submit(pool, func, opaque, opaque_destroy);
+    thread_pool_adjust_max_threads_to_work(pool);
+}
+
+void thread_pool_wait(ThreadPool *pool)
+{
+    QEMU_LOCK_GUARD(&pool->cur_work_lock);
+
+    while (pool->cur_work > 0) {
+        qemu_cond_wait(&pool->all_finished_cond,
+                       &pool->cur_work_lock);
+    }
+}
+
+bool thread_pool_set_max_threads(ThreadPool *pool,
+                                 int max_threads)
+{
+    assert(max_threads > 0);
+
+    return g_thread_pool_set_max_threads(pool->t, max_threads, NULL);
+}
+
+bool thread_pool_adjust_max_threads_to_work(ThreadPool *pool)
+{
+    QEMU_LOCK_GUARD(&pool->cur_work_lock);
+
+    return thread_pool_set_max_threads(pool, pool->cur_work);
+}