Hello, this is my first post on allegro.cc. Actually, I'm not used to posting on the internet at all (usually when I run into a programming problem I just use a search engine until I find a way to fix it), so this post is probably going to be rather stilted. I apologize in advance.
While working on a heavy C++11 wrapper for Allegro 5 to use in my game engine (which is not really an engine, just a large collection of classes), I encountered a problem when using al_detach_voice(), and also al_detach_mixer(), where the ALLEGRO_MIXER is one that is attached to an ALLEGRO_VOICE.
The problem is that, every ~5 to ~20 program executions, the code will hang at a call to al_detach_voice(). GDB says the problem occurs starting from this line, in addons/audio/kcm_voice.c, at line 379. I can provide a full backtrace if needed.
#SelectExpand
1voice->driver->stop_voice(voice);
Further inspection of GDB's backtrace would seem to indicate that Allegro is using the pulseaudio driver, but I would not know if this is specific to that driver.
I have tested and found that the exact same problem can be demonstrated with al_detach_mixer() as well (according to GDB, both call into the same underlying code in addons/audio/kcm_voice.c).
The version of Allegro I am using is Allegro 5.0.10 (debug) - the latest stable, I believe. I have not tested the WIP version, mainly because I want to use the stable release, but if someone needs me to test the unstable version, I can (assuming I can convince GCC to compile it, that is).
Here is an example program which should demonstrate the problem. You may need to run the program several times; I am able to reproduce the problem more or less reliably that way. Sometimes the program will deadlock/hang at the very first call to al_detach_voice().
#SelectExpand
1
2// This program is intended to demonstrate a possible problem in
3// al_detach_voice().
4
5#include <allegro5/allegro.h>
6#include <allegro5/allegro_audio.h>
7
8#include <iostream>
9#include <cassert>
10
11
12
13int main
(int /* argc */,
char** /* argv */)
14{
15 std::cout
<< "Starting tests ..." << std::endl
;
16
17 // Initialize Allegro Base.
18 if(!al_init())
19 {
20 std::cout
<< "al_init() failed.";
21 return -1;
22 }
23
24 // Initialize Allegro Audio add-on.
25 if(!al_install_audio())
26 {
27 std::cout
<< "al_install_audio() failed.";
28 return -1;
29 }
30
31 // Sanity checks.
32 assert(al_is_system_installed());
33 assert(al_is_audio_installed());
34
35 ALLEGRO_VOICE* pVoice
= 0;
36 ALLEGRO_MIXER* pMixer
= 0;
37
38 // Configuration variables.
39 const unsigned int frequency
= 44100;
40 const ALLEGRO_CHANNEL_CONF channel_conf
= ALLEGRO_CHANNEL_CONF_2
;
41 const ALLEGRO_AUDIO_DEPTH audio_depth
= ALLEGRO_AUDIO_DEPTH_FLOAT32
;
42
43 // Create the voice and mixer.
44 pVoice
= al_create_voice(frequency, audio_depth, channel_conf
);
45
46 if(!pVoice
)
47 {
48 std::cout
<< "al_create_voice() failed." << std::endl
;
49 return -1;
50 }
51
52 assert(pVoice
);
53
54 pMixer
= al_create_mixer(frequency, audio_depth, channel_conf
);
55
56 if(!pMixer
)
57 {
58 std::cout
<< "al_create_mixer() failed." << std::endl
;
59 return -1;
60 }
61
62 // Sanity checks.
63 assert(pMixer
);
64 assert(pVoice
);
65
66 // Perform one initial attach/detach before the main test loop. Sometimes the
67 // program will hang on the very first call to al_detach_voice() or
68 // al_detach_mixer().
69 {
70 std::cout
<< "Test #0 ... ";
71 std::cout.flush
();
72 bool result
= al_attach_mixer_to_voice(pMixer, pVoice
);
73 assert(result
);
74 al_detach_voice(pVoice
);
75 assert(!al_get_mixer_attached(pMixer
));
76 std::cout
<< "\tsucceeded." << std::endl
;
77 }
78
79
80
81 // Begin testing al_attach_mixer_to_voice() and al_detach_voice() multiple
82 // times ...
83 for(int i
= 1; i
<= 1000; ++i
)
84 {
85 std::cout
<< "Test #" << i
<< " ... ";
86 std::cout.flush
();
87
88 bool result
= al_attach_mixer_to_voice(pMixer, pVoice
);
89 assert(result
);
90
91 // Here is one of the troublesome functions. It hangs within its call stack.
92 al_detach_voice(pVoice
);
93
94 // Calling this function instead of al_detach_voice() also demonstrates the
95 // same problem.
96 // al_detach_mixer(pMixer);
97
98 assert(!al_get_mixer_attached(pMixer
));
99 std::cout
<< "\tsucceeded." << std::endl
;
100 }
101
102
103
104 // Clean up.
105 assert(pMixer
);
106 assert(pVoice
);
107 al_destroy_mixer(pMixer
);
108 pMixer
= 0;
109 al_destroy_voice(pVoice
);
110 pVoice
= 0;
111
112 // Shutdown Allegro Audio add-on; Allegro Base.
113 al_uninstall_audio();
114 al_uninstall_system();
115
116 // Sanity checks.
117 assert(!al_is_system_installed());
118 assert(!al_is_audio_installed());
119 std::cout
<< "Tests finished." << std::endl
;
120 return 0;
121}
Yes, I know attaching and detaching 1000 times is generally not realistic. But any little imperfection in Allegro bugs me. 
I hope I am not accidentally disturbing the wrong part of the forum ....
If I missed something that someone will need, please let me know.
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