async: coroutine engine core, reference schedulers and the coroutine context

The Async Core ABI (zend_async_API.h): coroutines with a packed lifecycle,
scheduler slots (launch, enqueue-with-error, suspend, cancel, await),
switch/finish handler vectors, the awaiting-info vector, microtasks, and
the coroutine context — an embedded internal store for C extensions
(process-unique numeric keys) plus the userland zend_async_context_t
storage behind a provider-registered class. Fibers run as coroutines under
a scheduler; gc_collect_cycles() stays synchronous over a GC coroutine;
shutdown drains coroutines gracefully.

Two optional in-tree providers validate the ABI from both sides:
ext/test_scheduler, the C reference (gated by test_scheduler.enable), and
ext/async_scheduler_hook, the PHP bridge — Async\SchedulerHook +
Async\Scheduler (onLaunch/onShutdown/onFiber/onEnqueue/onSuspend/onDefer),
a coroutine-centric mandate of three hidden capabilities
(bindEntry/switchTo/currentCoroutine), explicit main replacement at every
end-of-main handover, and the Async\Context / Async\get_context() surface
over the engine storage.

Tests run both variants in one binary: upstream suites stay byte-for-byte
and run schedulerless; scheduler-adapted duplicates and the provider
suites opt in.

Author: EdmondDantes

Zend/tests/fibers/gc-generator-in-suspended-fiber.phpt

@@ -0,0 +1,42 @@
+--TEST--
+GC collects a cycle through a generator parked in Fiber::suspend() on a fiber stack
+--FILE--
+<?php
+
+class C {
+    public function __destruct() {
+        echo __METHOD__, "\n";
+    }
+}
+
+function gen() {
+    $c = new C();
+    $self = Fiber::getCurrent(); // cycle: fiber -> frames -> $self -> fiber
+    yield 1;
+    Fiber::suspend("from gen");
+    yield 2;
+}
+
+$fiber = new Fiber(function () {
+    $g = gen();
+    $g->current();
+    $g->next(); // parks in Fiber::suspend() inside the generator
+    echo "unreachable\n";
+});
+
+$fiber->start();
+print "1\n";
+
+// Still referenced: nothing to collect.
+gc_collect_cycles();
+print "2\n";
+
+$fiber = null;
+gc_collect_cycles();
+print "3\n";
+?>
+--EXPECT--
+1
+2
+C::__destruct
+3

Zend/zend.c

@@ -24,6 +24,7 @@
 #include "zend_API.h"
 #include "zend_exceptions.h"
 #include "zend_builtin_functions.h"
+#include "zend_async_API.h"
 #include "zend_ini.h"
 #include "zend_vm.h"
 #include "zend_dtrace.h"
@@ -831,6 +832,7 @@ static void executor_globals_ctor(zend_executor_globals *executor_globals) /* {{
 	executor_globals->current_fiber_context = NULL;
 	executor_globals->main_fiber_context = NULL;
 	executor_globals->active_fiber = NULL;
+	memset(&executor_globals->shutdown_context, 0, sizeof(executor_globals->shutdown_context));
 #ifdef ZEND_WIN32
 	zend_get_windows_version_info(&executor_globals->windows_version_info);
 #endif
@@ -1979,8 +1981,13 @@ ZEND_API zend_result zend_execute_script(int type, zval *retval, zend_file_handl
 			if (Z_TYPE(EG(user_exception_handler)) != IS_UNDEF) {
 				zend_user_exception_handler();
 			}
+
 			if (EG(exception)) {
-				ret = zend_exception_error(EG(exception), E_ERROR);
+				if (ZEND_ASYNC_CURRENT_COROUTINE == NULL) {
+					ret = zend_exception_error(EG(exception), E_ERROR);
+				} else {
+					ret = FAILURE;
+				}
 			}
 		}
 		zend_destroy_static_vars(op_array);