Date: Thu, 11 Dec 2008 16:26:38 +0200 From: Andriy Pylypenko <bamby@sippysoft.com> To: python@FreeBSD.org Subject: Problem with signals in threads in Python Message-ID: <4941231E.4050408@sippysoft.com>
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Hello,
Almost a year ago I've created an issue in Python's bugtracker but the
issue seems to be stuck since then so I'm sending the patch here in hope
it could be included in ports collection.
In short there is a problem in the Python that can be seen under FreeBSD
but not under MacOSX or Linux. If a Python program started a thread in
background then it can be impossible to interrupt the program with
Ctrl-C. Here is an example of such script:
some_time = 6000000 # seconds
class MyThread(Thread):
def run(self):
while (True):
time.sleep(some_time)
t = MyThread()
t.setDaemon(True)
t.start()
while(True):
select.select(None, None, None, some_time)
The reason why this problem is FreeBSD specific is that the FreeBSD has
different order of processing of signals.
The signal handler under FreeBSD fires up in the context of the last
started thread while under Linux signals are processed in the main
thread. It should be noted that both behaviors are standards conformant.
So to ensure that signal handler runs in the correct thread context the
developer should use pthread_sigmask(). Initially the Python contained
this code but starting from Python 2.4 it was thrown away.
The attached patch restores the code that ensures correct execution
context of the signal handler code.
The detailed description of the issue can be seen here:
http://bugs.python.org/issue1975
--
Kind regards,
Andriy Pylypenko
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Index: Python/thread_pthread.h
===================================================================
--- Python/thread_pthread.h (revision 60447)
+++ Python/thread_pthread.h (working copy)
@@ -149,6 +149,7 @@
{
pthread_t th;
int status;
+ sigset_t set, oset;
#if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
pthread_attr_t attrs;
#endif
@@ -178,6 +179,8 @@
pthread_attr_setscope(&attrs, PTHREAD_SCOPE_SYSTEM);
#endif
+ sigfillset(&set);
+ SET_THREAD_SIGMASK(SIG_BLOCK, &set, &oset);
status = pthread_create(&th,
#if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
&attrs,
@@ -187,6 +190,7 @@
(void* (*)(void *))func,
(void *)arg
);
+ SET_THREAD_SIGMASK(SIG_SETMASK, &oset, NULL);
#if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
pthread_attr_destroy(&attrs);
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