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author ImJezze <jezze@gmx.net>2016-02-21 11:48:45 +0100
committer ImJezze <jezze@gmx.net>2016-02-21 11:48:45 +0100
commitcc24a339d8c0517259084b5c178d784626ba965c (patch)
tree9868e9687b5802ae0a3733712a3bbeb3bc75c953 /3rdparty/libuv/docs/src/threadpool.rst
parentb5daabda5495dea5c50e17961ecfed2ea8619d76 (diff)
Merge remote-tracking branch 'refs/remotes/mamedev/master'
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+
+.. _threadpool:
+
+Thread pool work scheduling
+===========================
+
+libuv provides a threadpool which can be used to run user code and get notified
+in the loop thread. This thread pool is internally used to run all filesystem
+operations, as well as getaddrinfo and getnameinfo requests.
+
+Its default size is 4, but it can be changed at startup time by setting the
+``UV_THREADPOOL_SIZE`` environment variable to any value (the absolute maximum
+is 128).
+
+The threadpool is global and shared across all event loops. When a particular
+function makes use of the threadpool (i.e. when using :c:func:`uv_queue_work`)
+libuv preallocates and initializes the maximum number of threads allowed by
+``UV_THREADPOOL_SIZE``. This causes a relatively minor memory overhead
+(~1MB for 128 threads) but increases the performance of threading at runtime.
+
+.. note::
+ Note that even though a global thread pool which is shared across all events
+ loops is used, the functions are not thread safe.
+
+
+Data types
+----------
+
+.. c:type:: uv_work_t
+
+ Work request type.
+
+.. c:type:: void (*uv_work_cb)(uv_work_t* req)
+
+ Callback passed to :c:func:`uv_queue_work` which will be run on the thread
+ pool.
+
+.. c:type:: void (*uv_after_work_cb)(uv_work_t* req, int status)
+
+ Callback passed to :c:func:`uv_queue_work` which will be called on the loop
+ thread after the work on the threadpool has been completed. If the work
+ was cancelled using :c:func:`uv_cancel` `status` will be ``UV_ECANCELED``.
+
+
+Public members
+^^^^^^^^^^^^^^
+
+.. c:member:: uv_loop_t* uv_work_t.loop
+
+ Loop that started this request and where completion will be reported.
+ Readonly.
+
+.. seealso:: The :c:type:`uv_req_t` members also apply.
+
+
+API
+---
+
+.. c:function:: int uv_queue_work(uv_loop_t* loop, uv_work_t* req, uv_work_cb work_cb, uv_after_work_cb after_work_cb)
+
+ Initializes a work request which will run the given `work_cb` in a thread
+ from the threadpool. Once `work_cb` is completed, `after_work_cb` will be
+ called on the loop thread.
+
+ This request can be cancelled with :c:func:`uv_cancel`.
+
+.. seealso:: The :c:type:`uv_req_t` API functions also apply.