/* $OpenBSD: pthread_rwlock2.c,v 1.1 2019/03/04 08:23:05 semarie Exp $ */
/*
 * Copyright (c) 2019 Sebastien Marie <semarie@online.fr>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <err.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define LOOP_MAIN       64      /* number of loop to try */
#define NTHREADS        16      /* number of concurrents threads */

/*
 * start several threads that share a buffer protected by rwlock.
 *
 * for each thread, take lock rw to set the buffer, and next take lock
 * rd to read (print) the buffer content.
 */

static pthread_rwlock_t rwlock = PTHREAD_RWLOCK_INITIALIZER;
static char msg[128] = "default message";

void
set_msg(int self_n, char *new_msg)
{
        pthread_t self = pthread_self();

        if (pthread_rwlock_wrlock(&rwlock) != 0)
                err(EXIT_FAILURE, "set_msg: pthread_rwlock_wrlock");

        printf("%p: %d: set_msg\n", self, self_n);
        strlcpy(msg, new_msg, sizeof(msg));
        
        if (pthread_rwlock_unlock(&rwlock) != 0)
                err(EXIT_FAILURE, "set_msg: pthread_rwlock_unlock");
}

void
print_msg(int self_n)
{
        pthread_t self = pthread_self();
        
        if (pthread_rwlock_rdlock(&rwlock) != 0)
                err(EXIT_FAILURE, "print_msg: pthread_rwlock_rdlock");
                
        printf("%p: %d: msg: \"%s\"\n", self, self_n, msg);

        if (pthread_rwlock_unlock(&rwlock) != 0)
                err(EXIT_FAILURE, "print_msg: pthread_rwlock_unlock");
}

void *
run(void *data)
{
        int self_n = (int)data;
        pthread_t self = pthread_self();

        printf("%p: %d: enter run()\n", self, self_n);

        set_msg(self_n, "new message");
        print_msg(self_n);

        printf("%p: %d: exit run()\n", self, self_n);
        return NULL;
}

int
main(int argc, char *argv[])
{
        int i, j;

        /* enable some rthread debug code (env take precedence) */
        if (setenv("RTHREAD_DEBUG", "9", 0) == -1)
                err(EXIT_FAILURE, "setenv");

        /* test in loop */
        for (i=0; i < LOOP_MAIN; i++) {
                pthread_t handlers[NTHREADS];

                printf("main: %d\n", i);

                /* launch a serie of threads */
                for (j=0; j < NTHREADS; j++) {
                        if (pthread_create(&(handlers[j]), NULL,
                            &run, (void *)(long)j) != 0)
                                err(EXIT_FAILURE, "main: pthread_create");
                }

                /* wait for them to finish */
                for (j=0; j < NTHREADS; j++) {
                        if (pthread_join(handlers[j], NULL) != 0)
                                err(EXIT_FAILURE, "main: pthread_join");
                }
        }

        return EXIT_SUCCESS;
}