使用条件变量输出 Mandelbrot 的线程同步问题

Question

我尝试将线程与条件变量同步以输出曼德博，但我得到了错误的曼德博。 函数output_mandel_line 和compute_mandel_line 已给出并且是正确的。我做了 void *function() 和 int main()。我怀疑问题出在 mutex_lock 内的 if 语句。我尝试了不同的 if 或 while 语句，但无法修复它。也许我如何使用 cond_wait ，cond_broadcast 也存在问题。

/*
 * mandel.c
 *
 * A program to draw the Mandelbrot Set on a 256-color xterm.
 *
 */

#include <stdio.h>
#include <unistd.h>
#include <assert.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#include "mandel-lib.h"
#include <pthread.h>
#include <errno.h>
#define perror_pthread(ret, msg) \
        do { errno = ret; perror(msg); } while (0)
#define MANDEL_MAX_ITERATION 100000
int nthreads;
pthread_cond_t cond;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
/***************************
 * Compile-time parameters *
 ***************************/

/*
 * Output at the terminal is is x_chars wide by y_chars long
 */
int y_chars = 50;
int x_chars = 90;

/*
 * The part of the complex plane to be drawn:
 * upper left corner is (xmin, ymax), lower right corner is (xmax, ymin)
 */
double xmin = -1.8, xmax = 1.0;
double ymin = -1.0, ymax = 1.0;

/*
 * Every character in the final output is
 * xstep x ystep units wide on the complex plane.
 */
double xstep;
double ystep;

/*
 * This function computes a line of output
 * as an array of x_char color values.
 */
void compute_mandel_line(int line, int color_val[])
{
        /*
         * x and y traverse the complex plane.
         */
        double x, y;

        int n;
        int val;

        /* Find out the y value corresponding to this line */
        y = ymax - ystep * line;

        /* and iterate for all points on this line */
        for (x = xmin, n = 0; n < x_chars; x+= xstep, n++) {

                /* Compute the point's color value */
                val = mandel_iterations_at_point(x, y, MANDEL_MAX_ITERATION);
                if (val > 255)
                        val = 255;

                /* And store it in the color_val[] array */
                val = xterm_color(val);
                color_val[n] = val;
        }
}

/*
 * This function outputs an array of x_char color values
 * to a 256-color xterm.
 */
void output_mandel_line(int fd, int color_val[])
{
        int i;

        char point ='@';
        char newline='\n';

        for (i = 0; i < x_chars; i++) {
                /* Set the current color, then output the point */
                set_xterm_color(fd, color_val[i]);
                if (write(fd, &point, 1) != 1) {
                        perror("compute_and_output_mandel_line: write point");
                        exit(1);
                }
        }

        /* Now that the line is done, output a newline character */
        if (write(fd, &newline, 1) != 1) {
                perror("compute_and_output_mandel_line: write newline");
                exit(1);
        }
}



void *function(void *arg){
        int *number = (int*)arg,  line;

int color_val[x_chars];
        for(line = *number; line < y_chars; line+=nthreads){
                
compute_mandel_line(line,color_val);            
                pthread_mutex_lock(&mutex);

               output_mandel_line(1,color_val);
pthread_cond_signal(&cond);
if( line + nthreads < y_chars ) {

pthread_cond_wait(&cond,&mutex);
                                }
        
pthread_cond_signal(&cond);
                pthread_mutex_unlock(&mutex);

pthread_cond_broadcast(&cond);
}
free(arg);

return NULL;
}
int main(int argc, char **argv)
{
        if(argc != 2) {
                fprintf(stderr, "Wrong format");
                exit(1);
        }
        nthreads = atoi(argv[1]);
        int i;
        pthread_t t[nthreads];
        //pthread_t *t =(pthread_t*)malloc(nthreads * sizeof(pthread_t));

        //ret =(pthread_cond_t*)malloc(nthreads * sizeof(pthread_cond_t));
        int ret;

        xstep = (xmax - xmin) / x_chars;
        ystep = (ymax - ymin) / y_chars;

        pthread_cond_init(&cond, NULL);
pthread_mutex_init(&mutex, NULL);


        for( i=0; i<nthreads; i++){
                int* a = malloc(sizeof(int));
                *a = i;
                ret = pthread_create(&t[i], NULL , function , a);
                if(ret){
                        perror_pthread(ret,"error");
                        exit(1);
                }
        }
       

        for( i=0; i<nthreads; i++){
                ret = pthread_join(t[i],NULL);
                if(ret){
                        perror_pthread(ret,"error");
                        exit(1);
                }
        }

        pthread_cond_destroy(&cond);
    pthread_mutex_destroy(&mutex);


        /*
         * Allocate memory for threads and semaphores
         * draw the Mandelbrot Set, one line at a time.
         * Output is sent to file descriptor '1', i.e., standard output.
         */


        reset_xterm_color(1);
  return 0;
}

我尝试更改 if 语句和 cond_wait 、 cond_signal 的条件变量顺序

Answer 1

我看到我的问题中有一个错误，但是我仍然不明白如何将条件变量实现到曼德尔布罗特集中，我已经更新了前面的语句，因为我显然被误导了