980659a2ca
BACKGROUND: We have learned that on some systems timeout timers are inaccurate and might occasionally fire off too early. To make the multi_socket API work with this, we made libcurl execute timeout actions a bit early too if they are within our MULTI_TIMEOUT_INACCURACY. (added in commit 2c72732ebf, present since 7.21.0) Switching everything to the multi API made this inaccuracy problem slightly more notable as now everyone can be affected. Recently (commit 21091549c02) we tweaked that inaccuracy value to make timeouts more accurate and made it platform specific. We also figured out that we have code at places that check for fixed timeout values so they MUST NOT run too early as then they will not trigger at all (see commit be28223f35 and a691e044705) - so there are definitately problems with running timeouts before they're supposed to run. (We've handled that so far by adding the inaccuracy margin to those specific timeouts.) The libcurl multi_socket API tells the application with a callback that a timeout expires in N milliseconds (and it explicitly will not tell it again for the same timeout), and the application is then supposed to call libcurl when that timeout expires. When libcurl subsequently gets called with curl_multi_socket_action(...CURL_SOCKET_TIMEOUT...), it knows that the application thinks the timeout expired - and alas, if it is within the inaccuracy level libcurl will run code handling that handle. If the application says CURL_SOCKET_TIMEOUT to libcurl and _isn't_ within the inaccuracy level, libcurl will not consider the timeout expired and it will not tell the application again since the timeout value is still the same. NOW: This change introduces a modified behavior here. If the application says CURL_SOCKET_TIMEOUT and libcurl finds no timeout code to run, it will inform the application about the timeout value - *again* even if it is the same timeout that it already told about before (although libcurl will of course tell it the updated time so that it'll still get the correct remaining time). This way, we will not risk that the application believes it has done its job and libcurl thinks the time hasn't come yet to run any code and both just sit waiting. This also allows us to decrease the MULTI_TIMEOUT_INACCURACY margin, but that will be handled in a separate commit. A repeated timeout update to the application risk that the timeout will then fire again immediately and we have what basically is a busy-loop until the time is fine even for libcurl. If that becomes a problem, we need to address it.
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README
Curl is a command line tool for transferring data specified with URL
syntax. Find out how to use curl by reading the curl.1 man page or the
MANUAL document. Find out how to install Curl by reading the INSTALL
document.
libcurl is the library curl is using to do its job. It is readily
available to be used by your software. Read the libcurl.3 man page to
learn how!
You find answers to the most frequent questions we get in the FAQ document.
Study the COPYING file for distribution terms and similar. If you distribute
curl binaries or other binaries that involve libcurl, you might enjoy the
LICENSE-MIXING document.
CONTACT
If you have problems, questions, ideas or suggestions, please contact us
by posting to a suitable mailing list. See http://curl.haxx.se/mail/
All contributors to the project are listed in the THANKS document.
WEB SITE
Visit the curl web site for the latest news and downloads:
http://curl.haxx.se/
GIT
To download the very latest source off the GIT server do this:
git clone git://github.com/bagder/curl.git
(you'll get a directory named curl created, filled with the source code)
NOTICE
Curl contains pieces of source code that is Copyright (c) 1998, 1999
Kungliga Tekniska Högskolan. This notice is included here to comply with the
distribution terms.