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@@ -0,0 +1,114 @@
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+/* -*- mode:c; c-file-style:"k&r"; c-basic-offset: 4; tab-width:4; indent-tabs-mode:nil; mode:auto-fill; fill-column:78; -*- */
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+/* vim: set ts=4 sw=4 et tw=78 fo=cqt wm=0: */
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+
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+#define _GNU_SOURCE
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+#include <malloc.h>
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+#include <unistd.h>
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+#include <sys/types.h>
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+#include <sys/wait.h>
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+#include <signal.h>
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+#include <sched.h>
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+#include <stdio.h>
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+#include <sys/syscall.h>
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+#include <asm/prctl.h>
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+#include <linux/futex.h>
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+#include <assert.h>
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+
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+// 64kB stack
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+#define FIBER_STACK 1024 * 64
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+#define THREADS 2
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+static int myfutex = 0;
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+struct atomic_int {
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+ volatile int counter;
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+};
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+static struct atomic_int my_counter;
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+
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+static inline void atomic_inc (struct atomic_int * v)
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+{
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+ asm volatile( "lock; incl %0"
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+ : "+m" (v->counter));
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+}
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+
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+static int
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+futex(int *uaddr, int futex_op, int val,
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+ const struct timespec *timeout, int *uaddr2, int val3)
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+{
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+ return syscall(SYS_futex, uaddr, futex_op, val,
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+ timeout, uaddr, val3);
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+}
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+
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+int thread_function (void * argument)
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+{
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+ int *ptr = (int *) argument;
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+ int rv;
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+ atomic_inc(&my_counter);
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+
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+ // Sleep on the futex
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+ rv = futex(&myfutex, FUTEX_WAIT_BITSET, 0, NULL, NULL, *ptr);
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+ assert(rv == 0);
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+ //printf("child thread %d awakened\n", getpid());
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+ return 0;
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+}
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+
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+int main (int argc, const char ** argv)
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+{
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+ void * stacks[THREADS];
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+ pid_t pids[THREADS];
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+ int varx[THREADS];
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+ my_counter.counter = 0;
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+
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+ for (int i = 0; i < THREADS; i++) {
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+
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+ varx[i] = (1 << i);
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+
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+ // Allocate the stack
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+ stacks[i] = malloc(FIBER_STACK);
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+ if (stacks[i] == 0) {
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+ perror("malloc: could not allocate stack");
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+ _exit(1);
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+ }
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+
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+ // Call the clone system call to create the child thread
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+ pids[i] = clone(&thread_function, (void *) stacks[i] + FIBER_STACK,
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+ CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_VM,
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+ &varx[i]);
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+
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+ //printf("clone() creates new thread %d\n", pids[i]);
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+
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+ if (pids[i] == -1) {
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+ perror("clone");
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+ _exit(2);
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+ }
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+ }
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+
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+ // Make sure the threads are sleeping
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+ do {
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+ sleep(1);
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+ } while(my_counter.counter != THREADS);
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+
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+ printf("Waking up kiddos\n");
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+ /* Wake in reverse order */
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+ for (int i = THREADS-1; i >= 0; i--) {
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+ pid_t pid;
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+ int rv;
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+ int var = (1 << i);
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+
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+ // Wake up the thread
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+ rv = futex(&myfutex, FUTEX_WAKE_BITSET, 1, NULL, NULL, var);
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+ assert(rv == 1);
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+
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+ // Wait for the child thread to exit
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+ pid = waitpid(pids[i], NULL, __WALL);
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+ if (pid == -1) {
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+ perror("waitpid");
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+ _exit(3);
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+ }
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+
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+ // Free the stack
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+ free(stacks[i]);
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+ }
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+
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+ printf("Woke all kiddos\n");
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+
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+ return 0;
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+}
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Don Porter