Interrupting Threads with boost::thread::interrupt()

[Matthias Vallentin]

Hi folks,

I am having issues with boost::thread::interrupt(). As far as I
understood, calling this function will throw an exception in the
corresponding thread. How can deal with blocking functions, such as a
calls to accept() or when a thread is waiting on a condition variable
to change? Basically the thread blocks somewhere in a while (true) loop.

Injecting interruption points manually with
boost::this_thread::interruption_point() does not seem to help here
either. boost::thread::interrupt() (or interrupt_all in a thread_group),
simply does not return.

Regards,

Matthias

[dhruva]

Hi,

On Tue, Jun 17, 2008 at 2:43 PM, Matthias Vallentin

Post by Matthias Vallentin
corresponding thread. How can deal with blocking functions, such as a
calls to accept() or when a thread is waiting on a condition variable

FWIK, there is no way to get out of blocking calls elegantly. The way
to go about it is to use non-blocking calls. Wait for multiple objects
(on windows I have used this) where one of the object is an event. On
an interrupt, you set the event and the wait will return.
For 'select', SAMBA has a neat trick. They create a pipe, the select
call also listens on one end of this pipe. On a signal, the signal
handler writes a char to the pipe which makes the call to select
return.
For non-blocking accept, you could check the SAMBA implementation of
socketpair. In a single thread, they create a socket, bind, accept,
connect and return the pair of connected sockets.

-dhruva

[Anthony Williams]

Post by Matthias Vallentin
I am having issues with boost::thread::interrupt(). As far as I
understood, calling this function will throw an exception in the
corresponding thread. How can deal with blocking functions, such as a
calls to accept() or when a thread is waiting on a condition variable
to change? Basically the thread blocks somewhere in a while (true) loop.
Injecting interruption points manually with
boost::this_thread::interruption_point() does not seem to help here
either. boost::thread::interrupt() (or interrupt_all in a thread_group),
simply does not return.

boost::thread::interrupt() calls the interrupted thread to throw an
exception when it next reaches an interruption point with interruption
enabled. Interruption points are boost::this_thread::sleep,
boost::this_thread::interruption_point, boost::thread::join,
boost::condition_variable::wait and timed_ variants.

See
http://www.justsoftwaresolutions.co.uk/threading/thread-interruption-in-boost-thread-library.html

boost::thread::interrupt() should return almost immediately: it does
not wait for the thread to be interrupted.

Anthony

[Reynolds, John]

Matthias

I believe that only certain boost thread methods such as sleep can be interrupted. What you could do is a loop that calls select with a timeout and only call a blocking accept when there is socket activity or you could loop with a non-blocking accept.

I assume that asio does this much better than what I have described.

John Reynolds
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-----Original Message-----
From: boost-users-***@lists.boost.org [mailto:boost-users-***@lists.boost.org] On Behalf Of Matthias Vallentin
Sent: 17 June 2008 10:14
To: boost-***@lists.boost.org
Subject: [Boost-users] Interrupting Threads with boost::thread::interrupt()

Hi folks,

I am having issues with boost::thread::interrupt(). As far as I understood, calling this function will throw an exception in the corresponding thread. How can deal with blocking functions, such as a calls to accept() or when a thread is waiting on a condition variable to change? Basically the thread blocks somewhere in a while (true) loop.

Injecting interruption points manually with
boost::this_thread::interruption_point() does not seem to help here either. boost::thread::interrupt() (or interrupt_all in a thread_group), simply does not return.

Regards,

Matthias
--
Matthias Vallentin
***@icsi.berkeley.edu
pgp/gpg: 0x37F34C16

[Matthias Vallentin]

Post by Reynolds, John
I believe that only certain boost thread methods such as sleep can be
interrupted.

That summarizes pretty much my misunderstanding. In essence I did not
realize that only the methods outlined by Anthony are interruptable via
interrupt().

Post by Reynolds, John
What you could do is a loop that calls select with a
timeout and only call a blocking accept when there is socket activity
or you could loop with a non-blocking accept.
I assume that asio does this much better than what I have described.

Migrating to the non-blocking versions will probably do the trick. It
seems to be a reasonable thing to leverage boost::asio for this purpose.

Thanks for your help,

Matthias

(dhruva: I will probably resort to boost::asio although the Samba tricks
are indeed quite elegant.)