1 files changed, 268 insertions, 0 deletions
diff --git a/coroutine/pthread/Context.c b/coroutine/pthread/Context.c
new file mode 100644
index 0000000000..bbf2d4c1a9
--- /dev/null
+++ b/coroutine/pthread/Context.c
@@ -0,0 +1,268 @@
+/*
+ *  This file is part of the "Coroutine" project and released under the MIT License.
+ *
+ *  Created by Samuel Williams on 24/6/2021.
+ *  Copyright, 2021, by Samuel Williams.
+*/
+
+#include "Context.h"
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+
+static const int DEBUG = 0;
+
+static
+int check(const char * message, int result) {
+    if (result) {
+        switch (result) {
+            case EDEADLK:
+                if (DEBUG) fprintf(stderr, "deadlock detected result=%d errno=%d\n", result, errno);
+                break;
+            default:
+                if (DEBUG) fprintf(stderr, "error detected result=%d errno=%d\n", result, errno);
+                perror(message);
+        }
+    }
+
+    assert(result == 0);
+
+    return result;
+}
+
+void coroutine_initialize_main(struct coroutine_context * context) {
+    context->id = pthread_self();
+
+    check("coroutine_initialize_main:pthread_cond_init",
+        pthread_cond_init(&context->schedule, NULL)
+    );
+
+    context->shared = (struct coroutine_shared*)malloc(sizeof(struct coroutine_shared));
+    assert(context->shared);
+
+    context->shared->main = context;
+    context->shared->count = 1;
+
+    if (DEBUG) {
+        pthread_mutexattr_t attr;
+        pthread_mutexattr_init(&attr);
+        pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK);
+
+        check("coroutine_initialize_main:pthread_mutex_init",
+            pthread_mutex_init(&context->shared->guard, &attr)
+        );
+    } else {
+        check("coroutine_initialize_main:pthread_mutex_init",
+            pthread_mutex_init(&context->shared->guard, NULL)
+        );
+    }
+}
+
+static
+void coroutine_release(struct coroutine_context *context) {
+    if (context->shared) {
+        size_t count = (context->shared->count -= 1);
+
+        if (count == 0) {
+            if (DEBUG) fprintf(stderr, "coroutine_release:pthread_mutex_destroy(%p)\n", &context->shared->guard);
+            pthread_mutex_destroy(&context->shared->guard);
+            free(context->shared);
+        }
+
+        context->shared = NULL;
+
+        if (DEBUG) fprintf(stderr, "coroutine_release:pthread_cond_destroy(%p)\n", &context->schedule);
+        pthread_cond_destroy(&context->schedule);
+    }
+}
+
+void coroutine_initialize(
+    struct coroutine_context *context,
+    coroutine_start start,
+    void *stack,
+    size_t size
+) {
+    assert(start && stack && size >= 1024);
+
+    // We will create the thread when we first transfer, but save the details now:
+    context->shared = NULL;
+    context->start = start;
+    context->stack = stack;
+    context->size = size;
+}
+
+static
+int is_locked(pthread_mutex_t * mutex) {
+    int result = pthread_mutex_trylock(mutex);
+
+    // If we could successfully lock the mutex:
+    if (result == 0) {
+        pthread_mutex_unlock(mutex);
+        // We could lock the mutex, so it wasn't locked:
+        return 0;
+    } else {
+        // Otherwise we couldn't lock it because it's already locked:
+        return 1;
+    }
+}
+
+static
+void coroutine_guard_unlock(void * _context)
+{
+    struct coroutine_context * context = _context;
+
+    if (DEBUG) fprintf(stderr, "coroutine_guard_unlock:pthread_mutex_unlock\n");
+
+    check("coroutine_guard_unlock:pthread_mutex_unlock",
+        pthread_mutex_unlock(&context->shared->guard)
+    );
+}
+
+static
+void coroutine_wait(struct coroutine_context *context)
+{
+    if (DEBUG) fprintf(stderr, "coroutine_wait:pthread_mutex_lock(guard=%p is_locked=%d)\n", &context->shared->guard, is_locked(&context->shared->guard));
+    check("coroutine_wait:pthread_mutex_lock",
+        pthread_mutex_lock(&context->shared->guard)
+    );
+
+    if (DEBUG) fprintf(stderr, "coroutine_wait:pthread_mutex_unlock(guard)\n");
+    pthread_mutex_unlock(&context->shared->guard);
+}
+
+static
+void coroutine_trampoline_cleanup(void *_context) {
+    struct coroutine_context * context = _context;
+    coroutine_release(context);
+}
+
+void * coroutine_trampoline(void * _context)
+{
+    struct coroutine_context * context = _context;
+    assert(context->shared);
+
+    pthread_cleanup_push(coroutine_trampoline_cleanup, context);
+
+    coroutine_wait(context);
+
+    context->start(context->from, context);
+
+    pthread_cleanup_pop(1);
+
+    return NULL;
+}
+
+static
+int coroutine_create_thread(struct coroutine_context *context)
+{
+    int result;
+
+    pthread_attr_t attr;
+    result = pthread_attr_init(&attr);
+    if (result != 0) {
+        return result;
+    }
+
+    result = pthread_attr_setstack(&attr, context->stack, (size_t)context->size);
+    if (result != 0) {
+        pthread_attr_destroy(&attr);
+        return result;
+    }
+
+    result = pthread_cond_init(&context->schedule, NULL);
+    if (result != 0) {
+        pthread_attr_destroy(&attr);
+        return result;
+    }
+
+    result = pthread_create(&context->id, &attr, coroutine_trampoline, context);
+    if (result != 0) {
+        pthread_attr_destroy(&attr);
+        if (DEBUG) fprintf(stderr, "coroutine_create_thread:pthread_cond_destroy(%p)\n", &context->schedule);
+        pthread_cond_destroy(&context->schedule);
+        return result;
+    }
+
+    context->shared->count += 1;
+
+    return result;
+}
+
+struct coroutine_context * coroutine_transfer(struct coroutine_context * current, struct coroutine_context * target)
+{
+    assert(current->shared);
+
+    struct coroutine_context * previous = target->from;
+    target->from = current;
+
+    if (DEBUG) fprintf(stderr, "coroutine_transfer:pthread_mutex_lock(guard=%p is_locked=%d)\n", &current->shared->guard, is_locked(&current->shared->guard));
+    pthread_mutex_lock(&current->shared->guard);
+    pthread_cleanup_push(coroutine_guard_unlock, current);
+
+    // First transfer:
+    if (target->shared == NULL) {
+        target->shared = current->shared;
+
+        if (DEBUG) fprintf(stderr, "coroutine_transfer:coroutine_create_thread...\n");
+        if (coroutine_create_thread(target)) {
+            if (DEBUG) fprintf(stderr, "coroutine_transfer:coroutine_create_thread failed\n");
+            target->shared = NULL;
+            target->from = previous;
+            return NULL;
+        }
+    } else {
+        if (DEBUG) fprintf(stderr, "coroutine_transfer:pthread_cond_signal(target)\n");
+        pthread_cond_signal(&target->schedule);
+    }
+
+    // A side effect of acting upon a cancellation request while in a condition wait is that the mutex is (in effect) re-acquired before calling the first cancellation cleanup handler. If cancelled, pthread_cond_wait immediately invokes cleanup handlers.
+    if (DEBUG) fprintf(stderr, "coroutine_transfer:pthread_cond_wait(schedule=%p, guard=%p, is_locked=%d)\n", &current->schedule, &current->shared->guard, is_locked(&current->shared->guard));
+    check("coroutine_transfer:pthread_cond_wait",
+        pthread_cond_wait(&current->schedule, &current->shared->guard)
+    );
+
+    if (DEBUG) fprintf(stderr, "coroutine_transfer:pthread_cleanup_pop\n");
+    pthread_cleanup_pop(1);
+
+#ifdef __FreeBSD__
+    // Apparently required for FreeBSD:
+    pthread_testcancel();
+#endif
+
+    target->from = previous;
+
+    return target;
+}
+
+static
+void coroutine_join(struct coroutine_context * context) {
+    if (DEBUG) fprintf(stderr, "coroutine_join:pthread_cancel\n");
+    check("coroutine_join:pthread_cancel",
+        pthread_cancel(context->id)
+    );
+
+    if (DEBUG) fprintf(stderr, "coroutine_join:pthread_join\n");
+    check("coroutine_join:pthread_join",
+        pthread_join(context->id, NULL)
+    );
+
+    if (DEBUG) fprintf(stderr, "coroutine_join:pthread_join done\n");
+}
+
+void coroutine_destroy(struct coroutine_context * context)
+{
+    if (DEBUG) fprintf(stderr, "coroutine_destroy\n");
+
+    assert(context);
+
+    // We are already destroyed or never created:
+    if (context->shared == NULL) return;
+
+    if (context == context->shared->main) {
+        context->shared->main = NULL;
+        coroutine_release(context);
+    } else {
+        coroutine_join(context);
+        assert(context->shared == NULL);
+    }
+}