On 04/04/07, malc <[EMAIL PROTECTED]> wrote:
On Wed, 4 Apr 2007, andrzej zaborowski wrote:
> Hi, thanks for quick response!
>
> On 03/04/07, malc <[EMAIL PROTECTED]> wrote:
>> On Tue, 3 Apr 2007, andrzej zaborowski wrote:
[..snip..]
> It should be using ALSA.
>
>>
>> Here's my theory: signal will be delivered to the arbitrary thread
>> that happens to not block it, for whatever reason, the thread SDL
>> created to do audio processing is picked up, which leads to some
>> system call being interrupted(eventually) and -1 (errno == EINTR), SDL
>> happily continues calling stuff.
Actually the signal can be just handled (by whatever signal handler
QEMU installed with sigaction) in a SDL created thread, so things can,
and mostlikely will, be silently wrong, i.e. EINTR while possible will
not necessarily happen.
>
> Yes, reading the PTHREAD_SIGNAL(3) note, this sounds very likely.
>
>>
>> One solution would be to explicitly block everything upon entering
>> sdl_callback for the first time. This is ugly and can have any
>> consequences one cares to imagine, but that's SDL for you (any
>> particular reason why you are using it?)
>
> Not really - just had only OSS and SDL compiled into qemu at this moment.
>
> Yes, the suggested solution works. Unfortunately it's neither pretty
> nor correct, because at the time sdl_callback runs, the signal which
> was supposed to wake up sigwait() is already lost and I can't find any
> way to prevent that - we can add a kill(0, SIGUSR2) but this is even
> uglier and again we don't know when sdl_callback is called as a result
> of this signal and when legally. (That's also why I didn't put a
> "return" after pthread_sigmask().)
[..snip..]
> What POSIX needs is a way to set the default signal mask for new threads :-/
http://www.opengroup.org/onlinepubs/007908799/xsh/pthread_create.html
in part reads
<quote>
The signal state of the new thread is initialised as follows:
* The signal mask is inherited from the creating thread.
</quote>
Oh, right.
Hence sequence of:
sigfillset (newset)
pthread_sigmask (SIG_BLOCK, newset, oldset)
SDL_OpenAudio (...)
pthread_sigmask (SGI_SETMASK, oldset, NULL)
Will probably achieve the desired effect.
Thanks, this works!
Attached is a patch, should be safe to apply. We're still making the
assumption that the thread is created precisely in SDL_OpenAudio and
not later, but this should not be a problem because all signals in the
main thread should be blocked throughout the entire runtime.
Regards,
Andrzej
From 6843399e5e751e999f33de09e4476f7c96839974 Mon Sep 17 00:00:00 2001
From: Andrzej Zaborowski <[EMAIL PROTECTED]>
Date: Wed, 4 Apr 2007 15:18:20 +0200
Subject: [PATCH] Ensure signals are properly masked for new SDL Audio threads.
---
audio/sdlaudio.c | 18 ++++++++++++++++++
1 files changed, 18 insertions(+), 0 deletions(-)
diff --git a/audio/sdlaudio.c b/audio/sdlaudio.c
index f2a6896..11edab0 100644
--- a/audio/sdlaudio.c
+++ b/audio/sdlaudio.c
@@ -25,6 +25,13 @@
#include <SDL_thread.h>
#include "vl.h"
+#ifndef _WIN32
+#ifdef __sun__
+#define _POSIX_PTHREAD_SEMANTICS 1
+#endif
+#include <signal.h>
+#endif
+
#define AUDIO_CAP "sdl"
#include "audio_int.h"
@@ -177,11 +184,22 @@ static int sdl_to_audfmt (int sdlfmt, audfmt_e *fmt, int
*endianess)
static int sdl_open (SDL_AudioSpec *req, SDL_AudioSpec *obt)
{
int status;
+#ifndef _WIN32
+ sigset_t new, old;
+
+ /* Make sure potential threads created by SDL don't hog signals. */
+ sigfillset (&new);
+ pthread_sigmask (SIG_BLOCK, &new, &old);
+#endif
status = SDL_OpenAudio (req, obt);
if (status) {
sdl_logerr ("SDL_OpenAudio failed\n");
}
+
+#ifndef _WIN32
+ pthread_sigmask (SIG_SETMASK, &old, 0);
+#endif
return status;
}
--
1.4.4.3
