Re: [9fans] C-program error..

Re: [9fans] C-program error..

[dhog]

In your example, s in recvit() is expected (by recv()) to point to
storage for the data sent on the channel (all 32 bytes worth),
but you have left it uninitialized.

Also, print() has an internal buffer of 4096 bytes; you need to
increase the stack size or you'll get mysterious errors caused
by stack corruption.

Try this version:

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

#define STACKSIZE (8*1024)

void
recvit(void *arg)
{
	char *s;
	Channel *in = arg;

	recv(in, &s);
	print("%s\n", s);
	free(s);
}

void
threadmain(int argc, char *argv[])
{
	char *m;
	Channel *sch;

	sch = chancreate(sizeof(char*), 0);
	m = strdup("hello world!");
	print("main: %s\n", m);
	proccreate(recvit, (void *)sch, STACKSIZE);

	send(sch, &m);

	print("done\n");
}

Re: [9fans] C-program error..

[rsc]

A few problems.  The main one is that you
sent a 32-byte array and tried to read it
into what was pointed at by an uninitialized pointer.
Compiling with -w would catch this.

The second is that you need to use threadprint
instead of print to avoid stack problems.
Threadprint is like fprint, so you need
to give a file descriptor.

The below works for me.

Russ


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

#define STACKSIZE (2*2048)

void
recvit(void *arg)
{
	char *s;
	Channel *in;	/* of char* */

	in = arg;
	s = recvp(in);
	threadprint(1, "%s\n", s);
	threadexits(0);
}

void
threadmain(int argc, char *argv[])
{
	Channel *sch;	/* of char* */

	sch = chancreate(sizeof(char*), 0);
	proccreate(recvit, (void *)sch, STACKSIZE);
	sendp(sch, "hello world");
	threadprint(1, "done\n");
	threadexitsall(nil);
}

[9fans] C-program error..

[Ish Rattan]

Hello,

Just tried translation of an old alef program. The program
aborts with run time error. Source and output given below.

Any pointers?
- ishwar
----
/* First C program, uses channel and procs..
	dies horribly..
*/

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

#define STACKSIZE (2*2048)

void recvit(void *arg)
{
   char *s;
   Channel *in = arg;

   recv(in, s);
   print("%s\n", s);
}

void threadmain(int argc, char *argv[])
{
   char m[32];
   Channel *sch;

   sch = chancreate(sizeof(m), 0);
   strcpy(m, "hello world!");
   print("main: %s\n", m);
   proccreate(recvit, (void *)sch, STACKSIZE);

   send(sch, m);

   print("done\n");
   exits(nil);
}
---
main: hello world!
 done
hello world!
panic: D2B called on non-block 510a8
8.out 513: suicide: sys: trap: fault read addr=0x0 pc=0x00003fd1
---