Date: Tue, 07 Sep 2010 17:38:06 +0000 From: David Xu <davidxu@freebsd.org> To: Jilles Tjoelker <jilles@stack.nl> Cc: freebsd-threads@freebsd.org Subject: Re: sigwait() cancellation point Message-ID: <4C86787E.6070908@freebsd.org> In-Reply-To: <20100906220041.GA4729@stack.nl> References: <20100906220041.GA4729@stack.nl>
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Jilles Tjoelker wrote: > Our sigwait() implementation may not be POSIX-compliant as it returns > EINTR when it is interrupted by a caught signal. (Unfortunately I can > only find this in SUSv4 in the Rationale, B.2.3 Error Numbers, > Disallowing Return of the [EINTR] Error Code; the sigwait() page in XSH > does not list an [EINTR] error condition, but does not prohibit one > either like pthread_mutex_lock() and various others do.) > > However, libthr's wrapper for sigwait() relies on EINTR. To keep > the possibility of changing this to be what POSIX intends, it would be > nice to remove this dependency. > > One way is to include SIGCANCEL in the set of waited signals, but this > requires two additional syscalls to mask/unmask SIGCANCEL. > > Another way is to use sigwaitinfo() in the wrapper, which is permitted > to return [EINTR]. If [EINTR] is removed from the kernel sigwait(), > looping on [EINTR] can then be implemented in the wrapper. > > Calling pthread_exit from the SIGCANCEL handler is not possible as this > leaves the program in doubt about any signal consumed by sigwait(). > I have worked out a patch: http://people.freebsd.org/~davidxu/patch/sigwait.diff
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