解析Linux进程为什么会进入睡眠模式

#include <stdio.h>
#include <pthread.h>

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
int shared_resource = 0;

void* thread_function(void* arg) {
    pthread_mutex_lock(&mutex);
    shared_resource++;
    pthread_mutex_unlock(&mutex);
    return NULL;
}

int main() {
    pthread_t thread;
    pthread_create(&thread, NULL, thread_function, NULL);
    
    pthread_mutex_lock(&mutex);
    while (shared_resource == 0) {
        pthread_mutex_unlock(&mutex);
        sched_yield(); // 主动让出CPU，避免忙等待
        pthread_mutex_lock(&mutex);
    }
    pthread_mutex_unlock(&mutex);

    pthread_join(thread, NULL);
    
    return 0;
}

#include <stdio.h>
#include <signal.h>

int main() {
    sigset_t set;
    int sig_no;
    sigemptyset(&set);
    sigaddset(&set, SIGUSR1);
    sigprocmask(SIG_BLOCK, &set, NULL);
    sigwait(&set, &sig_no);
    printf("Received signal SIGUSR1
");
    return 0;
}

#include <stdio.h>
#include <sys/select.h>

int main() {
    fd_set rfds;
    struct timeval tv;
    int retval;

    FD_ZERO(&rfds);
    FD_SET(0, &rfds);

    tv.tv_sec = 5;
    tv.tv_usec = 0;

    retval = select(1, &rfds, NULL, NULL, &tv);
    if (retval == -1) {
        perror("select()");
    } else if (retval) {
        printf("Data is available now.
");
    } else {
        printf("No data within five seconds.
");
    }

    return 0;
}