Bulletin number:  56
Products affected: D711D
Description: soft channels in threads
Component: compiler
Date: Fri May 4 15:18:42 BST 1990
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There have been reports of strangely behaving C programs which use
soft channels with threads. Such symptoms as binaries running fine on
say a B008 and then failing on a B016. This can be caused by using
soft channels to communicate between threads and their parent main()
or another sibling thread. These channels should have memory malloced
for them as illustrated in the example program below. If this is not
done then all channels have NULL pointers and so use the same word in
memory. This arrangement may work fine on occasions when the channel
communications do not trample over each other. If, as in a B016, the
running order of processes can be altered say by VME buss activity
then chaos may ensue.

#include <chan.h>
#include <thread.h>
#include <stdio.h> 

CHAN *to_thread, *from_thread;

main(argc,argv,envp,in_ports,ins,out_ports,outs)
int argc,ins,outs;
char *argv[],*envp[];
CHAN *in_ports[],*out_ports[];
{
   extern void thread();
   int news = 0;

   /*!!!>>  Allocate memory to channels  <<!!! */
   to_thread = malloc(sizeof(CHAN));
   from_thread = malloc(sizeof(CHAN));
   
   /* Initialise channel before use */
   chan_init(from_thread);
   chan_init(to_thread);

   thread_create(thread, 5000, 1, 1);
   for(;;) {
      chan_out_word(news,to_thread);	 /* sync to par task */
      chan_in_word(&news,from_thread);  /* receive word from thread */
      printf("News=%d\n",news++);
   }
}

/* thread communicates with main process via internal channel word */

void thread(i)
int i;
{
   int temp;

   for(;;) {
      chan_in_word(&temp,to_thread);  /* receive word from main process*/
      chan_out_word(temp,from_thread);  /* send word to main process */
   }
}