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1
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2 .. _threadpool:
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3
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4 Thread pool work scheduling
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5 ===========================
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6
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7 libuv provides a threadpool which can be used to run user code and get notified
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8 in the loop thread. This thread pool is internally used to run all file system
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9 operations, as well as getaddrinfo and getnameinfo requests.
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10
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11 Its default size is 4, but it can be changed at startup time by setting the
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12 ``UV_THREADPOOL_SIZE`` environment variable to any value (the absolute maximum
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13 is 1024).
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14
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15 .. versionchanged:: 1.30.0 the maximum UV_THREADPOOL_SIZE allowed was increased from 128 to 1024.
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16
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17 .. versionchanged:: 1.45.0 threads now have an 8 MB stack instead of the
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18 (sometimes too low) platform default.
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19
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20 .. versionchanged:: 1.50.0 threads now have a default name of libuv-worker.
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21
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22 The threadpool is global and shared across all event loops. When a particular
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23 function makes use of the threadpool (e.g. when using :c:func:`uv_queue_work`)
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24 libuv preallocates and initializes the maximum number of threads allowed by
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25 ``UV_THREADPOOL_SIZE``. More threads usually means more throughput but a higher
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26 memory footprint. Thread stacks grow lazily on most platforms though.
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27
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28 .. note::
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29 Note that even though a global thread pool which is shared across all events
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30 loops is used, the functions are not thread safe.
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31
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32
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33 Data types
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34 ----------
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35
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36 .. c:type:: uv_work_t
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37
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38 Work request type.
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39
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40 .. c:type:: void (*uv_work_cb)(uv_work_t* req)
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41
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42 Callback passed to :c:func:`uv_queue_work` which will be run on the thread
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43 pool.
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44
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45 .. c:type:: void (*uv_after_work_cb)(uv_work_t* req, int status)
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46
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47 Callback passed to :c:func:`uv_queue_work` which will be called on the loop
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48 thread after the work on the threadpool has been completed. If the work
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49 was cancelled using :c:func:`uv_cancel` `status` will be ``UV_ECANCELED``.
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50
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51
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52 Public members
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53 ^^^^^^^^^^^^^^
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54
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55 .. c:member:: uv_loop_t* uv_work_t.loop
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56
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57 Loop that started this request and where completion will be reported.
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58 Readonly.
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59
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60 .. seealso:: The :c:type:`uv_req_t` members also apply.
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61
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62
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63 API
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64 ---
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65
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66 .. 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)
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67
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68 Initializes a work request which will run the given `work_cb` in a thread
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69 from the threadpool. Once `work_cb` is completed, `after_work_cb` will be
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70 called on the loop thread.
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71
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72 This request can be cancelled with :c:func:`uv_cancel`.
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73
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74 .. seealso:: The :c:type:`uv_req_t` API functions also apply.
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