Question

我在我的程序中使用pthread.h和semaphore.h，并且包含了这些库。但是，似乎虽然我可以调用一些线程函数（例如pthread_exit()）并创建信号量变量，但我不能使用其他函数，例如sem_wait。我收到了来自Eclipse的undefined reference投诉。知道为什么会这样吗？在下面的代码中，semaphore.h中的void *thread1(void* v)函数不起作用。错误日志位于代码下方。

#define _GNU_SOURCE
#include <time.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <fcntl.h>
#include <semaphore.h>
#include <pthread.h>

typedef long long ll;
sem_t mutex;
int num=0;

void A(void);

void handler(void *ptr)
{
    pthread_exit(0);
}

double calculateAverage(double *arr, int len)
{
    double average=0.00;
    //first sum up all entries
    for(int i=0;i<len;i++)
    {
        average+=arr[i];
    }
    return average;
}

static inline ll timespec_to_ns(const struct timespec *tv)
{
    return ((ll) tv->tv_sec * 1000000000) + tv->tv_nsec;
}
ll beginMeasureTime() {
    struct timespec t;
    clock_gettime(CLOCK_MONOTONIC, &t);
    return timespec_to_ns(&t);
}
ll endMeasureTime(ll beginTime) {
    struct timespec t;
    clock_gettime(CLOCK_MONOTONIC, &t);
    return timespec_to_ns(&t)-beginTime;
}

ll measureFunctionCall(int n) {
    ll beginTime=beginMeasureTime();
    for(int i=0;i<n;i++) {
        A();
    }
    return endMeasureTime(beginTime);
}
ll measureSyscall(int n) {
    ll beginTime=beginMeasureTime();
    for(int i=0;i<n;i++) {
        syscall(SYS_getpid);
    }
    return endMeasureTime(beginTime);
}
ll measureProcessSwitch(int n) {
    int p[2];
    int p1[2];
    char arr;
    ll t=-1;
    // 0 for read 1 for writing
    if(pipe(p)<0) {
        perror("pipe");
        return -1;
    }
    if(pipe(p1)<0) {
        perror("pipe");
        goto out1;
    }
    int pid=fork();
    if(pid<0) {
        perror("fork");
        goto out2;
    }
    if(pid==0)
    {
        while(1)
        {
            if(read(p[0],&arr,1)<=0) _exit(1);
            if(write(p1[1],&arr,1)<=0) _exit(1);
        }
        _exit(0);
    }
    ll beginTime=beginMeasureTime();
    for(int i=0;i<n;i++){
        if(write(p[1],&arr,1)<=0) {
            perror("write");
            goto out2;
        }
        if(read(p1[0],&arr,1)<=0) {
            perror("read");
            goto out2;
        }
    }
    t=endMeasureTime(beginTime);
out2:
    close(p1[0]);
    close(p1[1]);
out1:
    close(p[0]);
    close(p[1]);
    return t;
}

typedef struct {
    sem_t s1;   //parent->child
    sem_t s2;   //child->parent
    int abort;
} info;

void* thread1(void* v) {
    info* inf=(info*)v;
    while(1)
    {
        if( sem_wait(&inf->s1) < 0) break;
        if(inf->abort) break;
        sem_post(&inf->s2);
    }
    return NULL;
}
ll measureThreadSwitch(int n) {
    info inf;
    inf.abort=0;
    ll t=-1;
    // 0 for read 1 for writing
    if(sem_init(&inf.s1,0,0)<0) {
        perror("sem_init");
        return -1;
    }
    if(sem_init(&inf.s2,0,0)<0) {
        perror("sem_init");
        goto out1;
    }
    pthread_t th;
    if(pthread_create(&th,NULL,&thread1,&inf)<0) {
        perror("pthread_create");
        goto out2;
    }

    ll beginTime=beginMeasureTime();
    for(int i=0;i<n;i++){
        if(sem_post(&inf.s1)<0) {
            perror("sem_post");
            goto out3;
        }
        if(sem_wait(&inf.s2)<0)  {
            perror("sem_wait");
            goto out3;
        }
    }
    t=endMeasureTime(beginTime);
out3:
    //thread is still running; need to signal to it to exit
    //and wait for it to exit
    inf.abort=1;
    sem_post(&inf.s1);
    pthread_join(th,NULL);
out2:
    sem_destroy(&inf.s2);
out1:
    sem_destroy(&inf.s1);
    return t;
}



int main(int argc, char **argv)
{
    if(argc <2)
    {
        printf("You entered less than two arguements\n");
        exit(-2);
    }
    if(argv[1] <0)
    {
        printf("you entered a negative argument\n");
        exit(-1);
    }
    int n=(atoi(argv[1]));

    printf("function call: %lld ns\n",measureFunctionCall(n)/n);
    printf("system call: %lld ns\n",measureSyscall(n)/n);
    printf("process switching: %lld ns\n",measureProcessSwitch(n)/n);
    printf("thread switching: %lld ns\n",measureThreadSwitch(n)/n);
}

/home/anb1/workspace/test/Debug/../src/test.c:123: undefined reference to sem_wait” /home/anb1/workspace/test/Debug/../src/test.c:125：对sem_post' ./src/test.o: In function measureThreadSwitch'的未定义引用： /home/anb1/workspace/test/Debug/../src/test.c:134：对sem_init' /home/anb1/workspace/test/Debug/../src/test.c:138: undefined reference to sem_init'的未定义引用 /home/anb1/workspace/test/Debug/../src/test.c:143：对pthread_create' /home/anb1/workspace/test/Debug/../src/test.c:150: undefined reference to sem_post'的未定义引用 /home/anb1/workspace/test/Debug/../src/test.c:154：对sem_wait' /home/anb1/workspace/test/Debug/../src/test.c:164: undefined reference to sem_post'的未定义引用 /home/anb1/workspace/test/Debug/../src/test.c:165：对pthread_join' /home/anb1/workspace/test/Debug/../src/test.c:167: undefined reference to sem_destroy'的未定义引用 /home/anb1/workspace/test/Debug/../src/test.c:169：对sem_destroy' collect2: error: ld returned 1 exit status make: *** [test] Error 1的未定义引用

Answer 1

您通过包含正确的头文件来编译程序，但必须正确链接。访问https://www.eclipse.org/forums/index.php/t/332260/，因为它反映了您在Eclipse中必须做的事情。你必须包括的是pthread库。

图书馆看起来只是部分包括在内，C和Eclipse

1 个答案: