Subject: Re: [boost] [Boost-users] Brainstorming [WAS: Subject: Formal Review of Proposed Boost.Process library starts tomorrow]
From: Jeremy Maitin-Shepard (jeremy_at_[hidden])
Date: 2011-02-14 16:02:38
On 02/14/2011 01:00 PM, Jeremy Maitin-Shepard wrote:
> On 02/14/2011 12:50 PM, Oliver Kowalke wrote:
>> Am 14.02.2011 21:14, schrieb Jeremy Maitin-Shepard:
>>> SIGCHLD handler will repeatedly invoke waitpid(-1, &status, WNOHANG |
>>> WUNTRACED | WCONTINUED), and then invoke any registered handlers.
>>
>> why polling - it waists CPU cycles?
>> I expect that the thread waiting for child processes state change blocks
>> (gets suspended) until it is notified by the kernel that something has
>> happened.
>> other worker-thread do other stuff like communicating with other process
>> etc.
>
> It wouldn't poll indefinitely, as that would lock up the thread in which
> the signal handler was invoked. It is simply invoked repeatedly until
> the error ECHILD (meaning no more unwaited-for children) is returned.
> The notification is in the form of SIGCHLD, but that just means one or
> more children need to be waited on.
Sorry, it is invoked repeatedly until waitpid returns 0.