Add coroutine implementation with setjmp/longjmp

Author: jserv

README.md

@@ -6,6 +6,7 @@ purpose of these programs is to be illustrative and educational.
 
 ## Project Listing
 * [Coroutine](https://en.wikipedia.org/wiki/Coroutine)
+    - [coro](coro/): A coroutine implementation with setjmp/longjmp.
     - [tinync](tinync/): A tiny `nc` implementation using coroutine.
     - [fiber](fiber/): A user-level thread (fiber) using `clone` system call.
     - [preempt\_sched](preempt_sched/): A preemptive userspace multitasking based on a SIGALRM signal.

coro/Makefile

@@ -0,0 +1,6 @@
+CFLAGS = -O2 -Wall
+all:
+	gcc $(CFLAGS) -o coro coro.c
+
+clean:
+	rm -f coro

coro/coro.c

@@ -0,0 +1,135 @@
+/* Implementing coroutines with setjmp/longjmp */
+
+#include <setjmp.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "list.h"
+
+struct task {
+    jmp_buf env;
+    struct list_head list;
+};
+
+static LIST_HEAD(tasklist);
+static void (**tasks)(void *);
+static int ntasks;
+static jmp_buf sched;
+
+static void task_add(struct list_head *tasklist, jmp_buf env)
+{
+    struct task *t = malloc(sizeof(*t));
+    memcpy(t->env, env, sizeof(jmp_buf));
+    INIT_LIST_HEAD(&t->list);
+    list_add_tail(&t->list, tasklist);
+}
+
+static void task_switch(struct list_head *tasklist)
+{
+    jmp_buf env;
+
+    if (!list_empty(tasklist)) {
+        struct task *t = list_first_entry(tasklist, struct task, list);
+        list_del(&t->list);
+        memcpy(env, t->env, sizeof(jmp_buf));
+        free(t);
+        longjmp(env, 1);
+    }
+}
+
+static void task_join(struct list_head *tasklist)
+{
+    jmp_buf env;
+
+    while (!list_empty(tasklist)) {
+        struct task *t = list_first_entry(tasklist, struct task, list);
+        list_del(&t->list);
+        memcpy(env, t->env, sizeof(jmp_buf));
+        free(t);
+        longjmp(env, 1);
+    }
+}
+
+void schedule(void)
+{
+    static int i;
+
+    srand(0xCAFEBABE ^ (uintptr_t) &schedule); /* Thanks to ASLR */
+
+    setjmp(sched);
+
+    while (ntasks-- > 0) {
+        int n = rand() % 5;
+        tasks[i++](&n);
+        printf("Never reached\n");
+    }
+
+    task_join(&tasklist);
+}
+
+/* A task yields control n times */
+
+void task0(void *arg)
+{
+    jmp_buf env;
+    static int n;
+    n = *(int *) arg;
+
+    printf("Task 0: n = %d\n", n);
+
+    if (setjmp(env) == 0) {
+        task_add(&tasklist, env);
+        // Jump back to scheduler
+        longjmp(sched, 1);
+    }
+
+    for (int i = 0; i < n; i++) {
+        if (setjmp(env) == 0) {
+            task_add(&tasklist, env);
+            task_switch(&tasklist);
+        }
+        printf("Task 0: resume\n");
+    }
+
+    printf("Task 0: complete\n");
+    longjmp(sched, 1);
+}
+
+void task1(void *arg)
+{
+    jmp_buf env;
+    static int n;
+    n = *(int *) arg;
+
+    printf("Task 1: n = %d\n", n);
+
+    if (setjmp(env) == 0) {
+        task_add(&tasklist, env);
+        // Jump back to scheduler
+        longjmp(sched, 1);
+    }
+
+    for (int i = 0; i < n; i++) {
+        if (setjmp(env) == 0) {
+            task_add(&tasklist, env);
+            task_switch(&tasklist);
+        }
+        printf("Task 1: resume\n");
+    }
+
+    printf("Task 1: complete\n");
+    longjmp(sched, 1);
+}
+
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
+int main(void)
+{
+    void (*registered_task[])(void *) = {task0, task1};
+    tasks = registered_task;
+    ntasks = ARRAY_SIZE(registered_task);
+
+    schedule();
+
+    return 0;
+}