Re: [9fans] alt..?

Re: [9fans] alt..?

[Sape Mullender]

I tried that code.  It doesn't crash.  Neither is it supposed to.
What is strange in the construction

        switch(alt(a)) {
          case 0:
                pval = recvp(a[0].c);
                threadprint(1, "alrmproc: request: %d, %x\n", pval->timer,
                        pval->mine);
                break;
          default:
                threadprint(2, "wow!");
        }

is that you receive from a[0].c twice, ignoring the first value
you receive.  When alt() returns (zero in the example above) it
will have put the received value in the location pointed to by
a[0].v (pval, in your case).  You probably don't want a recvp
call inside the switch on alt().

	Sape

Re: [9fans] alt..?

[Sape Mullender]

You were right, there IS a bug associated with CAHNNOBLK.
In line 86 of /sys/src/libthread/channel.c, replace `continue'
with `break'.  Sorry about that.

	Sape

[9fans] alt..?

[Ish Rattan]

One more problem. I am trying to translate the `alef' alarmproc example
(from Vol2. Alef User's Guide -- 2nd Ed). The code is given below.

1. When `a[1]' entry is {nil, nil, CHANEND} -- only one message is
recevied on a[0].c

main: chan: 510c8
alrmproc: request: 2, 510c8
main: done
(the first and the third one are lost..)

2. When a[1] is made {nil, nil, CHANNOBLK} --- program does suicide trap..

main: chan: 510c8
wow!8.out 2331: suicide: ...

Any pointers on nature of `alt' will be appreciated.

- ishwar
----
/* Alarm queue scenario, using synchronous and asynchronous
 * channels..	*/

#include <u.h>
#include <libc.h>
#include <thread.h>

#define STKSIZE (2*2048)

typedef struct alinfo {
	int timer;
	Channel *mine;
} alinfo;


void alrmproc(void *arg)
{
   alinfo *pval;
   Alt a[] = {	/* c  v  op */
		{nil, &pval, CHANRCV},
		{nil, nil, CHANEND},
	     };

   a[0].c = arg;

   for(;;) {
	switch(alt(a)) {
	  case 0:
		pval = recvp(a[0].c);
		threadprint(1, "alrmproc: request: %d, %x\n", pval->timer,
			pval->mine);
		break;
	  default:
		threadprint(2, "wow!");
	}

   }
}

void threadmain(int argc, char *argv[])
{
   alinfo out;
   Channel *cout;
   int i;

   cout = chancreate(sizeof(alinfo *), 0);
   threadprint(1, "main: chan: %x\n", cout);
   proccreate(alrmproc, (void *)cout, STKSIZE);

   out.mine = cout;
   for(i = 0; i< 3; i++) {
	out.timer = i+ 1;
        sendp(cout, &out);
   }
   sleep(4000);
   threadprint(1, "main: done\n");
}