From 02346abc32a3995299fa9c2f35b9f0a1d091b045 Mon Sep 17 00:00:00 2001 From: Daniel Stenberg Date: Mon, 29 Jul 2019 13:41:00 +0200 Subject: curl_multi_poll: a sister to curl_multi_wait() that waits more Repeatedly we see problems where using curl_multi_wait() is difficult or just awkward because if it has no file descriptor to wait for internally, it returns immediately and leaves it to the caller to wait for a small amount of time in order to avoid occasional busy-looping. This is often missed or misunderstood, leading to underperforming applications. This change introduces curl_multi_poll() as a replacement drop-in function that accepts the exact same set of arguments. This function works identically to curl_multi_wait() - EXCEPT - for the case when there's nothing to wait for internally, as then this function will by itself wait for a "suitable" short time before it returns. This effectiely avoids all risks of busy-looping and should also make it less likely that apps "over-wait". This also changes the curl tool to use this funtion internally when doing parallel transfers and changes curl_easy_perform() to use it internally. Closes #4163 --- docs/libcurl/Makefile.inc | 1 + docs/libcurl/curl_multi_poll.3 | 110 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 111 insertions(+) create mode 100644 docs/libcurl/curl_multi_poll.3 (limited to 'docs') diff --git a/docs/libcurl/Makefile.inc b/docs/libcurl/Makefile.inc index b4ff45dde..bd88c9c38 100644 --- a/docs/libcurl/Makefile.inc +++ b/docs/libcurl/Makefile.inc @@ -46,6 +46,7 @@ man_MANS = \ curl_multi_info_read.3 \ curl_multi_init.3 \ curl_multi_perform.3 \ + curl_multi_poll.3 \ curl_multi_remove_handle.3 \ curl_multi_setopt.3 \ curl_multi_socket.3 \ diff --git a/docs/libcurl/curl_multi_poll.3 b/docs/libcurl/curl_multi_poll.3 new file mode 100644 index 000000000..9fc72c55d --- /dev/null +++ b/docs/libcurl/curl_multi_poll.3 @@ -0,0 +1,110 @@ +.\" ************************************************************************** +.\" * _ _ ____ _ +.\" * Project ___| | | | _ \| | +.\" * / __| | | | |_) | | +.\" * | (__| |_| | _ <| |___ +.\" * \___|\___/|_| \_\_____| +.\" * +.\" * Copyright (C) 1998 - 2019, Daniel Stenberg, , et al. +.\" * +.\" * This software is licensed as described in the file COPYING, which +.\" * you should have received as part of this distribution. The terms +.\" * are also available at https://curl.haxx.se/docs/copyright.html. +.\" * +.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell +.\" * copies of the Software, and permit persons to whom the Software is +.\" * furnished to do so, under the terms of the COPYING file. +.\" * +.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY +.\" * KIND, either express or implied. +.\" * +.\" ************************************************************************** +.TH curl_multi_poll 3 "29 Jul 2019" "libcurl 7.66.0" "libcurl Manual" +.SH NAME +curl_multi_poll - polls on all easy handles in a multi handle +.SH SYNOPSIS +.nf +#include + +CURLMcode curl_multi_poll(CURLM *multi_handle, + struct curl_waitfd extra_fds[], + unsigned int extra_nfds, + int timeout_ms, + int *numfds); +.ad +.SH DESCRIPTION +\fIcurl_multi_poll(3)\fP polls all file descriptors used by the curl easy +handles contained in the given multi handle set. It will block until activity +is detected on at least one of the handles or \fItimeout_ms\fP has passed. +Alternatively, if the multi handle has a pending internal timeout that has a +shorter expiry time than \fItimeout_ms\fP, that shorter time will be used +instead to make sure timeout accuracy is reasonably kept. + +The calling application may pass additional curl_waitfd structures which are +similar to \fIpoll(2)\fP's pollfd structure to be waited on in the same call. + +On completion, if \fInumfds\fP is non-NULL, it will be populated with the +total number of file descriptors on which interesting events occurred. This +number can include both libcurl internal descriptors as well as descriptors +provided in \fIextra_fds\fP. + +If no extra file descriptors are provided and libcurl has no file descriptor +to offer to wait for, this function will instead wait during \fItimeout_ms\fP +milliseconds (or shorter if an internal timer indicates so). This is the +detail that makes this function different than \fIcurl_multi_wait(3)\fP. + +This function is encouraged to be used instead of select(3) when using the +multi interface to allow applications to easier circumvent the common problem +with 1024 maximum file descriptors. +.SH curl_waitfd +.nf +struct curl_waitfd { + curl_socket_t fd; + short events; + short revents; +}; +.fi +.IP CURL_WAIT_POLLIN +Bit flag to curl_waitfd.events indicating the socket should poll on read +events such as new data received. +.IP CURL_WAIT_POLLPRI +Bit flag to curl_waitfd.events indicating the socket should poll on high +priority read events such as out of band data. +.IP CURL_WAIT_POLLOUT +Bit flag to curl_waitfd.events indicating the socket should poll on write +events such as the socket being clear to write without blocking. +.SH EXAMPLE +.nf +CURL *easy_handle; +CURLM *multi_handle; + +/* add the individual easy handle */ +curl_multi_add_handle(multi_handle, easy_handle); + +do { + CURLMcode mc; + int numfds; + + mc = curl_multi_perform(multi_handle, &still_running); + + if(mc == CURLM_OK) { + /* wait for activity or timeout */ + mc = curl_multi_poll(multi_handle, NULL, 0, 1000, &numfds); + } + + if(mc != CURLM_OK) { + fprintf(stderr, "curl_multi failed, code %d.\\n", mc); + break; + } + +} while(still_running); + +curl_multi_remove_handle(multi_handle, easy_handle); +.fi +.SH RETURN VALUE +CURLMcode type, general libcurl multi interface error code. See +\fIlibcurl-errors(3)\fP +.SH AVAILABILITY +This function was added in libcurl 7.66.0. +.SH "SEE ALSO" +.BR curl_multi_fdset "(3), " curl_multi_perform "(3), " curl_multi_wait "(3)" -- cgit v1.2.3