1 2.. _threadpool: 3 4Thread pool work scheduling 5=========================== 6 7libuv provides a threadpool which can be used to run user code and get notified 8in the loop thread. This thread pool is internally used to run all file system 9operations, as well as getaddrinfo and getnameinfo requests. 10 11Its default size is 4, but it can be changed at startup time by setting the 12``UV_THREADPOOL_SIZE`` environment variable to any value (the absolute maximum 13is 1024). 14 15.. versionchanged:: 1.30.0 the maximum UV_THREADPOOL_SIZE allowed was increased from 128 to 1024. 16 17.. versionchanged:: 1.45.0 threads now have an 8 MB stack instead of the 18 (sometimes too low) platform default. 19 20The threadpool is global and shared across all event loops. When a particular 21function makes use of the threadpool (i.e. when using :c:func:`uv_queue_work`) 22libuv preallocates and initializes the maximum number of threads allowed by 23``UV_THREADPOOL_SIZE``. This causes a relatively minor memory overhead 24(~1MB for 128 threads) but increases the performance of threading at runtime. 25 26.. note:: 27 Note that even though a global thread pool which is shared across all events 28 loops is used, the functions are not thread safe. 29 30 31Data types 32---------- 33 34.. c:type:: uv_work_t 35 36 Work request type. 37 38.. c:type:: void (*uv_work_cb)(uv_work_t* req) 39 40 Callback passed to :c:func:`uv_queue_work` which will be run on the thread 41 pool. 42 43.. c:type:: void (*uv_after_work_cb)(uv_work_t* req, int status) 44 45 Callback passed to :c:func:`uv_queue_work` which will be called on the loop 46 thread after the work on the threadpool has been completed. If the work 47 was cancelled using :c:func:`uv_cancel` `status` will be ``UV_ECANCELED``. 48 49 50Public members 51^^^^^^^^^^^^^^ 52 53.. c:member:: uv_loop_t* uv_work_t.loop 54 55 Loop that started this request and where completion will be reported. 56 Readonly. 57 58.. seealso:: The :c:type:`uv_req_t` members also apply. 59 60 61API 62--- 63 64.. 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) 65 66 Initializes a work request which will run the given `work_cb` in a thread 67 from the threadpool. Once `work_cb` is completed, `after_work_cb` will be 68 called on the loop thread. 69 70 This request can be cancelled with :c:func:`uv_cancel`. 71 72.. seealso:: The :c:type:`uv_req_t` API functions also apply. 73
