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Bug 1192 - Restoring an app gets stuck in an infinite loop.
Summary: Restoring an app gets stuck in an infinite loop.
Status: RESOLVED FIXED
Alias: None
Product: SDL
Classification: Unclassified
Component: video (show other bugs)
Version: HG 2.0
Hardware: iPhone/iPod touch iOS (All)
: P2 blocker
Assignee: Sam Lantinga
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2011-04-27 17:57 UTC by Jeremy Jurksztowicz
Modified: 2012-01-06 22:44 UTC (History)
1 user (show)

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Description Jeremy Jurksztowicz 2011-04-27 17:57:52 UTC 
SDL_render_gles2.c, function [GLES2_CacheProgram]:

entry = rdata->program_cache.head; 
    while (entry) 
    {
        if (entry->vertex_shader == vertex && entry->fragment_shader == fragment) 
            break; 
        entry = entry->next;  // <-PROBLEM HERE
    }

The rdata->program_cache.head node's next and prev pointers point to itself, hence infinite loop.
Comment 1 Jeremy Jurksztowicz 2011-05-07 20:14:48 UTC 
The linked list code in SDL_render_gles2.c is faulty. It's actually a circular linked list.
Comment 2 Jeremy Jurksztowicz 2011-05-07 20:54:59 UTC 
This is a WORKAROUND, not a fix, as the linked list should be constructed properly.

Change:

    /* Check if we've already cached this program */
    entry = rdata->program_cache.head;
    while (entry)
    {
        if (entry->vertex_shader == vertex && entry->fragment_shader == fragment)
            break;
			
        entry = entry->next;
    }

To:

    /* Check if we've already cached this program */
    entry = rdata->program_cache.head;
    while (entry)
    {
        if (entry->vertex_shader == vertex && entry->fragment_shader == fragment)
            break;
			
		/* Quick 'n dirty hack! The linked list is not managed properly. */
		if(entry == rdata->program_cache.tail)
		{
			entry = 0;
			break;
		}
			
        entry = entry->next;
    }
Comment 3 Jeremy Jurksztowicz 2011-05-08 07:46:16 UTC 
FAIL! Last workaround screws up cache hit rate. This one is works by relying on the node count being accurate to avoid the infinite loop.

numCaches = rdata->program_cache.count; 
   if(numCaches < 0) 
      return NULL; 
       
    while (entry && numCaches) 
    { 
        if (entry->vertex_shader == vertex && entry->fragment_shader == fragment) 
            break; 
                
        entry = entry->next; 
       
      if(--numCaches <= 0) 
      { 
         entry = 0; 
         break; 
      } 
    }
Comment 4 Sam Lantinga 2012-01-06 22:44:11 UTC 
Hahah, yeah, I ran into this one myself and fixed it a couple months ago.  Can you take a look at the latest SDL snapshot and see if the fix looks good to you?
http://www.libsdl.org/tmp/SDL-1.3.zip