One Way to Suspend Another Thread In Linux

// at process start call init_pthread_suspending to install the handlers
// to suspend a thread use pthread_kill(thread_id, SUSPEND_SIG)
// to resume a thread use pthread_kill(thread_id, RESUME_SIG)

#include <signal.h>

#define RESUME_SIG SIGUSR2
#define SUSPEND_SIG SIGUSR1

static sigset_t wait_mask;
static __thread int suspended; // per-thread flag

void resume_handler(int sig)
{
    suspended = 0;
}

void suspend_handler(int sig)
{
    if (suspended) return;
    suspended = 1;
    do sigsuspend(&wait_mask); while (suspended);
}

void init_pthread_suspending()
{
    struct sigaction sa;

    sigfillset(&wait_mask);
    sigdelset(&wait_mask, SUSPEND_SIG)
    sigdelset(&wait_mask, RESUME_SIG);

    sigfillset(&sa.sa_mask);
    sa.sa_flags = 0;
    sa.sa_handler = resume_handler;
    sigaction(RESUME_SIG, &sa, NULL);

    sa.sa_handler = suspend_handler;
    sigaction(SUSPEND_SIG, &sa, NULL);
}