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- #define _GNU_SOURCE
- #include <asm/prctl.h>
- #include <assert.h>
- #include <linux/futex.h>
- #include <malloc.h>
- #include <sched.h>
- #include <signal.h>
- #include <stdio.h>
- #include <sys/syscall.h>
- #include <sys/types.h>
- #include <sys/wait.h>
- #include <unistd.h>
- // 64kB stack
- #define FIBER_STACK (1024 * 64)
- #define THREADS 2
- static int myfutex = 0;
- struct atomic_int {
- volatile int counter;
- };
- static struct atomic_int my_counter;
- static inline void atomic_inc(struct atomic_int* v) {
- asm volatile("lock; incl %0" : "+m"(v->counter));
- }
- static int futex(int* uaddr, int futex_op, int val, const struct timespec* timeout, int* uaddr2,
- int val3) {
- return syscall(SYS_futex, uaddr, futex_op, val, timeout, uaddr, val3);
- }
- int thread_function(void* argument) {
- int* ptr = (int*)argument;
- int rv;
- atomic_inc(&my_counter);
- // Sleep on the futex
- rv = futex(&myfutex, FUTEX_WAIT_BITSET, 0, NULL, NULL, *ptr);
- assert(rv == 0);
- // printf("child thread %d awakened\n", getpid());
- return 0;
- }
- int main(int argc, const char** argv) {
- void* stacks[THREADS];
- pid_t pids[THREADS];
- int varx[THREADS];
- my_counter.counter = 0;
- for (int i = 0; i < THREADS; i++) {
- varx[i] = (1 << i);
- // Allocate the stack
- stacks[i] = malloc(FIBER_STACK);
- if (stacks[i] == 0) {
- perror("malloc: could not allocate stack");
- _exit(1);
- }
- // Call the clone system call to create the child thread
- pids[i] = clone(&thread_function, (void*)stacks[i] + FIBER_STACK,
- CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_VM, &varx[i]);
- // printf("clone() creates new thread %d\n", pids[i]);
- if (pids[i] == -1) {
- perror("clone");
- _exit(2);
- }
- }
- // Make sure the threads are sleeping
- do {
- sleep(1);
- } while (my_counter.counter != THREADS);
- printf("Waking up kiddos\n");
- /* Wake in reverse order */
- for (int i = THREADS - 1; i >= 0; i--) {
- pid_t pid;
- int rv;
- int var = (1 << i);
- // Wake up the thread
- rv = futex(&myfutex, FUTEX_WAKE_BITSET, 1, NULL, NULL, var);
- assert(rv == 1);
- // Wait for the child thread to exit
- pid = waitpid(pids[i], NULL, __WALL);
- if (pid == -1) {
- perror("waitpid");
- _exit(3);
- }
- // Free the stack
- free(stacks[i]);
- }
- printf("Woke all kiddos\n");
- return 0;
- }
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