224 lines
5.6 KiB
HTML
224 lines
5.6 KiB
HTML
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lil-gp Bug Patches
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<H1> lil-gp Bug Patches</h1>
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<p> I have identified two chief bugs in lil-gpl 1.1 beta while working in multi-threaded mode. Until they are resolved, here are (ugly) patches to the code which should work nicely.
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<a href="http://www.daimi.aau.dk/~ptr/">Peter Anderson</a> has also identified a bug in lilgp's ERC facility; I've not verified this bug, but his patch is located <a href="peters-patch.html">here</a>.
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<h2>The Tree Evaluation Facility</h2>
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<p> This appears to be a <b>very</b> serious bug; all the function <tt>set_current_individual()</tt> does is modify a global static pointer. This creates a very dangerous race condition when individuals are being evaluated simultaneously. The patch is to move this global variable into the thread-safe globaldata structure. This means you will have to first add to your <b>globaldata</b> structure the line...
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<p><tt>individual* current_individual;</tt>
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<p>You should not access this line in your evaluation code, even though it's in the globaldata structure. Once this line has been added, follow the following patch instructions.
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<p><b>Open the file <tt>eval.c</tt>. Change the passage...</b>
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<P><pre><tt>
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static individual * current_individual;
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void set_current_individual ( individual *ind )
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{
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current_individual = ind;
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}
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</tt></pre>
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<p><b>...to...</b>
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<p><pre><tt>
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#if !defined(POSIX_MT) && !defined(SOLARIS_MT)
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static individual * current_individual;
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#define CURRENT_INDIVIDUAL current_individual
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#else
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#define CURRENT_INDIVIDUAL ((get_globaldata())->current_individual)
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#endif
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void set_current_individual ( individual *ind )
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{
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CURRENT_INDIVIDUAL = ind;
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}
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</tt></pre>
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<p><b>...next, there are THREE passages you'll need to change. They're all identical. All three times it occurs, change...</b>
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<p><pre><tt>
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arg->d = evaluate_tree ( current_individual->tr[f->evaltree].data,
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f->evaltree );
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</tt></pre>
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<p><b>...to...</b>
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<p><pre><tt>
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arg->d = evaluate_tree ( CURRENT_INDIVIDUAL->tr[f->evaltree].data,
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f->evaltree );
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</tt></pre>
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<h2>The Random Facility</h2>
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<p> lil-gp's random facility is not threadsafe and cannot be called from your evaluation code in multi-threaded mode without some patching. The patch for this wraps the random facility in a mutex so only one thread can call the random function at a time. Assuming threads aren't re-seeing the generator, the only function that needs to be wrapped is <tt>random_double()</tt> because the other random functions operate on it. <b>Note that this patch only works for POSIX Threads</b>. You'll have to code your own Solaris Threads patch, sorry. Here are the patch instructions.
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<p><b>First open <tt>main.c</tt>, and change the passage</b>
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<P><pre><tt>
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/* maximum number of nodes per individual. -1 if no limit is
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enforced. */
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int ind_nodelimit;
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int main ( int argc, char **argv )
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{
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multipop *mpop;
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int startgen;
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char *param;
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event start, end, diff;
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event eval, breed;
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int startfromcheckpoint;
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#ifdef MEMORY_LOG
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/* dump all memory allocations to a file. */
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mlog = fopen ( "memory.log", "w" );
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#endif
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</tt></pre>
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<p> <b>...to...</b>
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<p><pre><tt>
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/* maximum number of nodes per individual. -1 if no limit is
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enforced. */
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int ind_nodelimit;
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extern pthread_mutex_t random_mutex; /* Mutexes the random code */
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int main ( int argc, char **argv )
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{
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multipop *mpop;
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int startgen;
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char *param;
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event start, end, diff;
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event eval, breed;
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int startfromcheckpoint;
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pthread_mutex_init(&random_mutex,NULL); /* Initialize the random mutex */
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#ifdef MEMORY_LOG
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/* dump all memory allocations to a file. */
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mlog = fopen ( "memory.log", "w" );
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#endif
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</tt></pre>
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<p><b> Then modify the passage (at the end of <tt>main()</tt>)...</b>
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<p><pre><tt>
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/* print memory/time statistics and close output files. */
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output_system_stats ( &diff, &eval, &breed );
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close_output_streams();
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#ifdef MEMORY_LOG
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fclose ( mlog );
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#endif
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/* all done. */
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return 0;
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}
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</tt></pre>
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<p><b>...to...</b>
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<p><pre><tt>
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/* print memory/time statistics and close output files. */
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output_system_stats ( &diff, &eval, &breed );
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close_output_streams();
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#ifdef MEMORY_LOG
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fclose ( mlog );
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#endif
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pthread_mutex_destroy(&random_mutex); /* Destroy random mutex */
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/* all done. */
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return 0;
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}
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</tt></pre>
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<p><b> Next, open the file <tt>random.c</tt> Change the passage </b>
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<p><pre><tt>
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static double mz = 0.0;
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static double ma[55]; /* the number 55 is special -- see Knuth. */
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static int inext, inextp;
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</tt></pre>
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<p><b> ...to...</b>
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<p><pre><tt>
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static double mz = 0.0;
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static double ma[55]; /* the number 55 is special -- see Knuth. */
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static int inext, inextp;
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pthread_mutex_t random_mutex;
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</tt></pre>
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<p><b> and change the function...</b>
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<p><pre><tt>
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double random_double ( void )
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{
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double mj;
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double res;
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inext = (inext+1)%55;
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inextp = (inextp+1)%55;
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mj = ma[inext] - ma[inextp];
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if ( mj < mz )
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mj = mj + mbig;
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ma[inext] = mj;
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res=mbig;
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return mj/res;
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}
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</tt></pre>
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<p><b> ...to...</b>
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<p><pre><tt>
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double random_double ( void )
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{
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/* There's a race condition on this, so we need to mutex it! */
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double mj;
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double res;
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pthread_mutex_lock(&random_mutex);
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inext = (inext+1)%55;
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inextp = (inextp+1)%55;
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mj = ma[inext] - ma[inextp];
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if ( mj < mz )
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mj = mj + mbig;
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ma[inext] = mj;
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res=mbig;
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pthread_mutex_unlock(&random_mutex);
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return mj/res;
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}
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</tt></pre>
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