1 files changed, 125 insertions, 0 deletions
diff --git a/include/util/threadpool.h b/include/util/threadpool.h
new file mode 100644
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--- /dev/null
+++ b/include/util/threadpool.h
@@ -0,0 +1,125 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/*
+ * threadpool.h
+ *
+ * Copyright (C) 2021 David Oberhollenzer <goliath@infraroot.at>
+ */
+#ifndef THREADPOOL_H
+#define THREADPOOL_H
+
+#include "sqfs/predef.h"
+
+typedef int (*thread_pool_worker_t)(void *user, void *work_item);
+
+/**
+ * @struct thread_pool_t
+ *
+ * @brief A thread pool with a ticket number based work item ordering.
+ *
+ * While the order in which items are non-deterministic, the thread pool
+ * implementation internally uses a ticket system to ensure the completed
+ * items are deqeueued in the same order that they were enqueued.
+ */
+typedef struct thread_pool_t {
+	/**
+	 * @brief Shutdown and destroy a thread pool.
+	 *
+	 * @param pool A pointer to a pool returned by thread_pool_create
+	 */
+	void (*destroy)(struct thread_pool_t *pool);
+
+	/**
+	 * @brief Get the actual number of worker threads available.
+	 *
+	 * @return A number greater or equal to 1.
+	 */
+	size_t (*get_worker_count)(struct thread_pool_t *pool);
+
+	/**
+	 * @brief Change the user data pointer for a thread pool worker
+	 *        by index.
+	 *
+	 * @param idx A zero-based index into the worker list.
+	 * @param ptr A user pointer that this specific worker thread should
+	 *            pass to the worker callback.
+	 */
+	void (*set_worker_ptr)(struct thread_pool_t *pool, size_t idx,
+			       void *ptr);
+
+	/**
+	 * @brief Submit a work item to a thread pool.
+	 *
+	 * This function will fail on allocation failure or if the internal
+	 * error state is set was set by one of the workers.
+	 *
+	 * @param ptr A pointer to a work object to enqueue.
+	 *
+	 * @return Zero on success.
+	 */
+	int (*submit)(struct thread_pool_t *pool, void *ptr);
+
+	/**
+	 * @brief Wait for a work item to be completed.
+	 *
+	 * This function dequeues a single completed work item. It may block
+	 * until one of the worker threads signals completion of an additional
+	 * item.
+	 *
+	 * This function guarantees to return the items in the same order as
+	 * they were submitted, so the function can actually block longer than
+	 * necessary, because it has to wait until the next item in sequence
+	 * is finished.
+	 *
+	 * @return A pointer to a new work item or NULL if there are none
+	 *         in the pipeline.
+	 */
+	void *(*dequeue)(struct thread_pool_t *pool);
+
+	/**
+	 * @brief Get the internal worker return status value.
+	 *
+	 * If the worker functions returns a non-zero exit status in one of the
+	 * worker threads, the thread pool stors the value internally and shuts
+	 * down. This function can be used to retrieve the value.
+	 *
+	 * @return A non-zero value returned by the worker callback or zero if
+	 *         everything is A-OK.
+	 */
+	int (*get_status)(struct thread_pool_t *pool);
+} thread_pool_t;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Create a thread pool instance.
+ *
+ * @param num_jobs The number of worker threads to launch.
+ * @param worker A function to call from the worker threads to process
+ *               the work items.
+ *
+ * @return A pointer to a thread pool on success, NULL on failure.
+ */
+SQFS_INTERNAL thread_pool_t *thread_pool_create(size_t num_jobs,
+						thread_pool_worker_t worker);
+
+/**
+ * @brief Create a serial mockup thread pool implementation.
+ *
+ * This returns a @ref thread_pool_t implementation that, instead of running a
+ * thread pool actually does the work in-situ when dequeueing.
+ *
+ * @param worker A function to call from the worker threads to process
+ *               the work items.
+ *
+ * @return A pointer to a thread pool on success, NULL on failure.
+ */
+SQFS_INTERNAL
+thread_pool_t *thread_pool_create_serial(thread_pool_worker_t worker);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* THREADPOOL_H */