From: havoc <havoc@d7cf8633-e32d-0410-b094-e92efae38249>
Date: Mon, 23 May 2011 09:41:52 +0000 (+0000)
Subject: fix a crash in debug builds where the compiler did not optimize
X-Git-Tag: xonotic-v0.6.0~163^2~385
X-Git-Url: https://git.rm.cloudns.org/?a=commitdiff_plain;h=b812f1cdbdd266c770423017f47a129e64811cf0;p=xonotic%2Fdarkplaces.git

fix a crash in debug builds where the compiler did not optimize
ch->sfx-> to use a local variable holding the unchanging value of sfx
(the crash occurs when the mixer thread clears ch->sfx while the main
thread is deciding whether to merge a sound onto an existing channel -
if the channel dies during this code, the sfx pointer must be preserved)


git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@11161 d7cf8633-e32d-0410-b094-e92efae38249
---

diff --git a/snd_main.c b/snd_main.c
index fac45a4f..9265cb68 100644
--- a/snd_main.c
+++ b/snd_main.c
@@ -1200,6 +1200,7 @@ channel_t *SND_PickChannel(int entnum, int entchannel)
 	int first_to_die;
 	int first_life_left, life_left;
 	channel_t* ch;
+	sfx_t *sfx; // use this instead of ch->sfx->, because that is volatile.
 
 // Check for replacement sound, or find the best one to replace
 	first_to_die = -1;
@@ -1224,7 +1225,8 @@ channel_t *SND_PickChannel(int entnum, int entchannel)
 	for (ch_idx=NUM_AMBIENTS ; ch_idx < NUM_AMBIENTS + MAX_DYNAMIC_CHANNELS ; ch_idx++)
 	{
 		ch = &channels[ch_idx];
-		if (!ch->sfx)
+		sfx = ch->sfx; // fetch the volatile variable
+		if (!sfx)
 		{
 			// no sound on this channel
 			first_to_die = ch_idx;
@@ -1236,9 +1238,9 @@ channel_t *SND_PickChannel(int entnum, int entchannel)
 			continue;
 
 		// don't override looped sounds
-		if ((ch->flags & CHANNELFLAG_FORCELOOP) || ch->sfx->loopstart < ch->sfx->total_length)
+		if ((ch->flags & CHANNELFLAG_FORCELOOP) || sfx->loopstart < sfx->total_length)
 			continue;
-		life_left = ch->sfx->total_length - ch->pos;
+		life_left = sfx->total_length - ch->pos;
 
 		if (life_left < first_life_left)
 		{
@@ -1852,6 +1854,7 @@ void S_UpdateAmbientSounds (void)
 	int			ambient_channel;
 	channel_t	*chan;
 	unsigned char		ambientlevels[NUM_AMBIENTS];
+	sfx_t		*sfx;
 
 	memset(ambientlevels, 0, sizeof(ambientlevels));
 	if (cl.worldmodel && cl.worldmodel->brush.AmbientSoundLevelsForPoint)
@@ -1861,7 +1864,8 @@ void S_UpdateAmbientSounds (void)
 	for (ambient_channel = 0 ; ambient_channel< NUM_AMBIENTS ; ambient_channel++)
 	{
 		chan = &channels[ambient_channel];
-		if (chan->sfx == NULL || chan->sfx->fetcher == NULL)
+		sfx = chan->sfx; // fetch the volatile variable
+		if (sfx == NULL || sfx->fetcher == NULL)
 			continue;
 
 		vol = (int)ambientlevels[ambient_channel];
diff --git a/snd_main.h b/snd_main.h
index c7c631f8..7419e9ce 100644
--- a/snd_main.h
+++ b/snd_main.h
@@ -86,7 +86,7 @@ typedef struct channel_s
 {
 	int			listener_volume [SND_LISTENERS];	// 0-65536 volume per speaker
 	int				master_vol;		// 0-65536 master volume
-	sfx_t			*sfx;			// sfx number
+	sfx_t			*sfx;			// pointer to sound sample being used
 	unsigned int	flags;			// cf CHANNELFLAG_* defines
 	int				pos;			// sample position in sfx, negative values delay the start of the sound playback
 	int				entnum;			// to allow overriding a specific sound
diff --git a/snd_mix.c b/snd_mix.c
index 05abc83a..cc425bac 100644
--- a/snd_mix.c
+++ b/snd_mix.c
@@ -186,6 +186,11 @@ static qboolean SND_PaintChannel (channel_t *ch, portable_sampleframe_t *paint,
 	int vol[SND_LISTENERS];
 	const snd_buffer_t *sb;
 	unsigned int i, sb_offset;
+	sfx_t *sfx;
+
+	sfx = ch->sfx; // fetch the volatile variable
+	if (!sfx) // given that this is called by the mixer thread, this never happens, but...
+		return false;
 
 	// move to the stack (do we need to?)
 	for (i = 0;i < SND_LISTENERS;i++)
@@ -199,11 +204,11 @@ static qboolean SND_PaintChannel (channel_t *ch, portable_sampleframe_t *paint,
 		return false;
 
 	sb_offset = ch->pos;
-	sb = ch->sfx->fetcher->getsb (ch->sfx->fetcher_data, &ch->fetcher_data, &sb_offset, count);
+	sb = sfx->fetcher->getsb (sfx->fetcher_data, &ch->fetcher_data, &sb_offset, count);
 	if (sb == NULL)
 	{
 		Con_DPrintf("SND_PaintChannel: ERROR: can't get sound buffer from sfx \"%s\"\n",
-					ch->sfx->name); // , count); // or add this? FIXME
+					sfx->name); // , count); // or add this? FIXME
 		return false;
 	}
 	else