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| author | Dru Lavigne <dru@FreeBSD.org> | 2016-06-30 14:40:58 +0000 |
|---|---|---|
| committer | Dru Lavigne <dru@FreeBSD.org> | 2016-06-30 14:40:58 +0000 |
| commit | 75fa73dc6c1e3d5b73ac9d1c6123abaabc4d88d0 (patch) | |
| tree | d417453cd8fcd32f0b992b643d17b2ebd36dc65c | |
| parent | 716ed4e85751fdf5ec9be0c62c0f56a9ad66a16e (diff) | |
| download | doc-75fa73dc6c1e3d5b73ac9d1c6123abaabc4d88d0.tar.gz doc-75fa73dc6c1e3d5b73ac9d1c6123abaabc4d88d0.zip | |
Add robust mutexes report from kib@FreeBSD.org.
Reviewed by: wblock@freebsd.org
Sponsored by: iXsystems
Notes
Notes:
svn path=/head/; revision=49022
| -rw-r--r-- | en_US.ISO8859-1/htdocs/news/status/report-2016-04-2016-06.xml | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/en_US.ISO8859-1/htdocs/news/status/report-2016-04-2016-06.xml b/en_US.ISO8859-1/htdocs/news/status/report-2016-04-2016-06.xml index 73add06874..c389fe0b6d 100644 --- a/en_US.ISO8859-1/htdocs/news/status/report-2016-04-2016-06.xml +++ b/en_US.ISO8859-1/htdocs/news/status/report-2016-04-2016-06.xml @@ -244,4 +244,86 @@ interest.</task> </help> </project> + + <project cat='proj'> + <title>Robust Mutexes</title> + + <contact> + <person> + <name> + <given>Konstantin</given> + <common>Belousov</common> + </name> + <email>kib@FreeBSD.org</email> + </person> + <person> + <name> + <given>Ed</given> + <common>Maste</common> + </name> + <email>emaste@FreeBSD.org</email> + </person> + </contact> + + <body> + <p>Now that the process-shared locks are implemented for our + POSIX threads implementation library, <tt>libthr</tt>, + the only major lacking feature for POSIX compliance is robust + mutexes. Robust mutexes allow the application to detect, and + theoretically, recover from crashes which occur while + modifying the shared state. The supported model is to protect + shared state by a <tt>pthread_mutex</tt>, and the crash is + detected as the thread termination while owning the mutex. A + thread might terminate alone, or it could be killed due to the + termination of the containing process. As such, the robust + attribute is applicable to both process-private and -shared + mutexes.</p> + + <p>An application must be specifically modified to handle and + recover from failures. The <tt>pthread_mutex_lock()</tt> + function may return new error <tt>EOWNERDEAD</tt>, which + indicates that the previous owner of the lock terminated while + still owning the lock. Despite returning the non-zero value, + the lock is granted to the caller. In the simplest form, an + application may detect the error and refuse to operate until + the persistent shared data is recovered, such as by manual + reinitialization. More sophisticated applications could try + to automatically recover from the condition, in which case + <tt>pthread_mutex_consistent(3)</tt> must be called on the + lock before the unlock. However, such recovery can be + considered to be very hard. Still, even the detection of + inconsistent shared state is useful, since it avoids further + corruption and random faults of the affected application. + </p> + + <p>It is curious but not unexpected that this interface is not + used widely. The only real-life application which utilizes it + is Samba. Using Samba with an updated FreeBSD base uncovered + minor bugs both in the FreeBSD robustness implementation, and + in Samba itself.</p> + + <p>It is believed that <tt>libthr</tt> in FreeBSD 11 is + POSIX-compliant for large features. Further work is planned + to look at the lock structures inlining to remove overhead + and improve performance of the library.</p> + + <p>Most of the implementation of the robustness feature + consisted of making small changes in the lock and unlock + paths, both in <tt>libthr</tt> and in <tt>kern_umtx.c</tt>. + This literally required reading all of the code dealing with + mutexes and conditional variables, which was something I + wanted to help future developers with. In the end, with the + help of Ed Maste, the man pages for <tt>umtx(2)</tt> and all + <tt>thr*(2)</tt> syscalls were written and added to the base + system's documentation set. + </p> + </body> + + <sponsor>The FreeBSD Foundation</sponsor> + + <help> + <task>Use the implementation in real-word applications and + report issues.</task> + </help> + </project> </report> |