修改PID管理器以进行多线程seg故障

Question

当线程进入perform_work（）以创建新的pid时，它会在第二次尝试执行时发出分段错误。我必须配置我的线程创建错误，但我不知道在哪里。这个问题是对Modify PID manager for multi-threading

的跟进

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <assert.h>

#define MIN_PID 300
#define MAX_PID 5000
#define CB CHAR_BIT

#define NUM_THREADS 20

int sz = MAX_PID - MIN_PID + 1;

int id;
int i;
int map;

unsigned char *unsignedChar;

int allocate_map();
int allocate_pid();
void *perform_work();
void release_pid(int pid);

int main() 
{
    pthread_t threads[NUM_THREADS];
    int thread_args[NUM_THREADS];
    int result_code, index;

    //create all threads one by one
    for (index = 0; index < NUM_THREADS; ++index){
        thread_args[index] = index;
        printf("Creating thread %d\n", index);
        result_code = pthread_create(&threads[index], NULL, perform_work(), (void *) &thread_args[index]);
        assert(0 == result_code);
    }

    // wait for each thread to complete
    for (index = 0; index < NUM_THREADS; ++index) {
            // block until thread 'index' completes
            result_code = pthread_join(threads[index], NULL);
            printf("In main: thread %d has completed\n", index);
            assert(0 == result_code);
    }

    printf("In main: all threads completed successfully\n");

    //release a few processes
        release_pid(303); printf("\nProcess 303 released.");
        release_pid(308); printf("\nProcess 308 released.");
    release_pid(309); printf("\nProcess 309 released.");

    //allocate a few more processes after this release
        int val = allocate_pid(); printf("\nProcess %d : pid = %d", ++i, val); //should be 303
    val = allocate_pid(); printf("\nProcess %d : pid = %d\n", ++i, val); //should be 308
}

void *perform_work(void *argument){
    map = allocate_map();
    i = 0;
    id = 0;

    if (map == 1) {
        printf("\nBitmap Data Structure initialized.\n");

        int val = allocate_pid();
        printf("\nProcess %d: pid = %d\n", i+1, val);
        i++;
    }
    else printf("\nFailed to initialize data structure.\n");
}

/* Creates and initializes a bitmap data structure for representing pids;
 returns —1 for unsuccessful, 1 for successful */
int allocate_map() {
    unsignedChar = (unsigned char*)malloc((sz+CB-1)/CB * sizeof(char));
    if (unsignedChar) return 1;
    return -1;
}

/* Allocates and returns a pid; returns -1
if it is unable to allocate a pid (all pids are in use) */
int allocate_pid() {
    int i = 0;
    int pid = unsignedChar[i/CB] & (1 << (i & (CB-1)));
    while (pid != 0) {
        i++;
        pid = unsignedChar[i/CB] & (1 << (i & (CB-1)));
        }

    if (i+MIN_PID > MAX_PID) return -1;
    unsignedChar[i/CB] |= 1 << (i & (CB-1));
    return i+MIN_PID;
}

/* Releases a pid given a pid parameter*/
void release_pid(int pid) {
    if (pid < 300) {
        printf("\nInvalid PID: It should lie between 300 and 3000.");
        return;
    }
    int i = pid - MIN_PID;
    unsignedChar[i/CB] &= ~(1 << (i & (CB-1)));
}