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);
}