Store active Fiber instance separately from current fiber context

This allows another fiber abstraction to create fibers within a Fiber instance (or vice versa), while maintaining the behavior of Fiber::suspend() switching execution to the last call to Fiber::start/resume/throw.

Author: trowski

Zend/zend.c

@@ -774,7 +774,9 @@ static void executor_globals_ctor(zend_executor_globals *executor_globals) /* {{
 	executor_globals->exception_class = NULL;
 	executor_globals->exception = NULL;
 	executor_globals->objects_store.object_buckets = NULL;
-	executor_globals->current_fiber = NULL;
+	executor_globals->current_fiber_context = NULL;
+	executor_globals->main_fiber_context = NULL;
+	executor_globals->active_fiber = NULL;
 #ifdef ZEND_WIN32
 	zend_get_windows_version_info(&executor_globals->windows_version_info);
 #endif

Zend/zend_fibers.c

@@ -183,7 +183,7 @@ static void zend_fiber_stack_free(zend_fiber_stack *stack)
 
 static ZEND_NORETURN void zend_fiber_trampoline(transfer_t transfer)
 {
-	zend_fiber_context *context = EG(current_fiber);
+	zend_fiber_context *context = EG(current_fiber_context);
 	zend_fiber_context *from = transfer.data;
 
 	from->handle = transfer.context;
@@ -228,7 +228,7 @@ ZEND_API void zend_fiber_destroy_context(zend_fiber_context *context)
 
 ZEND_API zend_fiber_context *zend_fiber_switch_context(zend_fiber_context *to)
 {
-	zend_fiber_context *from = EG(current_fiber);
+	zend_fiber_context *from = EG(current_fiber_context);
 	zend_fiber_vm_state state;
 
 	ZEND_ASSERT(to && to->handle && "Invalid fiber context");
@@ -245,7 +245,7 @@ ZEND_API zend_fiber_context *zend_fiber_switch_context(zend_fiber_context *to)
 		from->status = ZEND_FIBER_STATUS_SUSPENDED;
 	}
 
-	EG(current_fiber) = to;
+	EG(current_fiber_context) = to;
 
 #ifdef __SANITIZE_ADDRESS__
 	void *fake_stack = NULL;
@@ -261,7 +261,7 @@ ZEND_API zend_fiber_context *zend_fiber_switch_context(zend_fiber_context *to)
 	__sanitizer_finish_switch_fiber(fake_stack, &to->stack.prior_pointer, &to->stack.prior_size);
 #endif
 
-	EG(current_fiber) = from;
+	EG(current_fiber_context) = from;
 
 	zend_fiber_context *previous = transfer.data;
 	previous->handle = transfer.context;
@@ -281,7 +281,6 @@ ZEND_API zend_fiber_context *zend_fiber_switch_context(zend_fiber_context *to)
 	return previous;
 }
 
-
 static zend_always_inline zend_vm_stack zend_fiber_vm_stack_alloc(size_t size)
 {
 	zend_vm_stack page = emalloc(size);
@@ -352,6 +351,23 @@ static ZEND_STACK_ALIGNED zend_fiber_context *zend_fiber_execute(zend_fiber_cont
 	return caller;
 }
 
+static void zend_fiber_switch_to(zend_fiber *fiber)
+{
+	zend_fiber *previous = EG(active_fiber);
+	fiber->caller = EG(current_fiber_context);
+	EG(active_fiber) = fiber;
+	zend_fiber_switch_context(zend_fiber_get_context(fiber));
+	EG(active_fiber) = previous;
+}
+
+static void zend_fiber_suspend(zend_fiber *fiber)
+{
+	zend_fiber_context *caller = fiber->caller;
+	ZEND_ASSERT(caller != NULL);
+	fiber->caller = NULL;
+	zend_fiber_switch_context(caller);
+}
+
 static zend_object *zend_fiber_object_create(zend_class_entry *ce)
 {
 	zend_fiber *fiber;
@@ -376,10 +392,9 @@ static void zend_fiber_object_destroy(zend_object *object)
 	zend_object *exception = EG(exception);
 	EG(exception) = NULL;
 
-	fiber->caller = EG(current_fiber);
 	fiber->flags |= ZEND_FIBER_FLAG_DESTROYED;
 
-	zend_fiber_switch_context(zend_fiber_get_context(fiber));
+	zend_fiber_switch_to(fiber);
 
 	if (EG(exception)) {
 		if (!exception && EG(current_execute_data) && EG(current_execute_data)->func
@@ -443,15 +458,11 @@ ZEND_METHOD(Fiber, start)
 	fiber->fci.param_count = param_count;
 	fiber->fci.named_params = named_params;
 
-	zend_fiber_context *context = zend_fiber_get_context(fiber);
-
-	if (!zend_fiber_init_context(context, zend_ce_fiber, zend_fiber_execute, EG(fiber_stack_size))) {
+	if (!zend_fiber_init_context(zend_fiber_get_context(fiber), zend_ce_fiber, zend_fiber_execute, EG(fiber_stack_size))) {
 		RETURN_THROWS();
 	}
 
-	fiber->caller = EG(current_fiber);
-
-	zend_fiber_switch_context(context);
+	zend_fiber_switch_to(fiber);
 
 	if (fiber->status == ZEND_FIBER_STATUS_DEAD) {
 		RETURN_NULL();
@@ -470,33 +481,30 @@ ZEND_METHOD(Fiber, suspend)
 		Z_PARAM_ZVAL(value);
 	ZEND_PARSE_PARAMETERS_END();
 
-	if (UNEXPECTED(EG(current_fiber)->kind != zend_ce_fiber)) {
+	zend_fiber *fiber = EG(active_fiber);
+
+	if (!fiber) {
 		zend_throw_error(zend_ce_fiber_error, "Cannot suspend outside of a fiber");
 		RETURN_THROWS();
 	}
 
-	zend_fiber *fiber = zend_fiber_from_context(EG(current_fiber));
-	zend_fiber_context *caller = fiber->caller;
-
 	if (UNEXPECTED(fiber->flags & ZEND_FIBER_FLAG_DESTROYED)) {
 		zend_throw_error(zend_ce_fiber_error, "Cannot suspend in a force-closed fiber");
 		RETURN_THROWS();
 	}
 
 	ZEND_ASSERT(fiber->status == ZEND_FIBER_STATUS_RUNNING);
-	ZEND_ASSERT(caller != NULL);
 
 	if (value) {
 		ZVAL_COPY(&fiber->value, value);
 	} else {
 		ZVAL_NULL(&fiber->value);
 	}
 
-	fiber->caller = NULL;
 	fiber->execute_data = EG(current_execute_data);
 	fiber->stack_bottom->prev_execute_data = NULL;
 
-	zend_fiber_switch_context(caller);
+	zend_fiber_suspend(fiber);
 
 	if (fiber->flags & ZEND_FIBER_FLAG_DESTROYED) {
 		// This occurs when the fiber is GC'ed while suspended.
@@ -539,10 +547,9 @@ ZEND_METHOD(Fiber, resume)
 		ZVAL_NULL(&fiber->value);
 	}
 
-	fiber->caller = EG(current_fiber);
 	fiber->stack_bottom->prev_execute_data = EG(current_execute_data);
 
-	zend_fiber_switch_context(zend_fiber_get_context(fiber));
+	zend_fiber_switch_to(fiber);
 
 	if (fiber->status == ZEND_FIBER_STATUS_DEAD) {
 		RETURN_NULL();
@@ -571,10 +578,9 @@ ZEND_METHOD(Fiber, throw)
 	Z_ADDREF_P(exception);
 	fiber->exception = exception;
 
-	fiber->caller = EG(current_fiber);
 	fiber->stack_bottom->prev_execute_data = EG(current_execute_data);
 
-	zend_fiber_switch_context(zend_fiber_get_context(fiber));
+	zend_fiber_switch_to(fiber);
 
 	if (fiber->status == ZEND_FIBER_STATUS_DEAD) {
 		RETURN_NULL();
@@ -659,11 +665,13 @@ ZEND_METHOD(Fiber, this)
 {
 	ZEND_PARSE_PARAMETERS_NONE();
 
-	if (EG(current_fiber)->kind != zend_ce_fiber) {
+	zend_fiber *fiber = EG(active_fiber);
+
+	if (!fiber) {
 		RETURN_NULL();
 	}
 
-	RETURN_OBJ_COPY(&zend_fiber_from_context(EG(current_fiber))->std);
+	RETURN_OBJ_COPY(&fiber->std);
 }
 
 ZEND_METHOD(FiberError, __construct)
@@ -698,11 +706,12 @@ void zend_fiber_init(void)
 
 	context->status = ZEND_FIBER_STATUS_RUNNING;
 
-	EG(main_fiber) = context;
-	EG(current_fiber) = context;
+	EG(main_fiber_context) = context;
+	EG(current_fiber_context) = context;
+	EG(active_fiber) = NULL;
 }
 
 void zend_fiber_shutdown(void)
 {
-	efree(EG(main_fiber));
+	efree(EG(main_fiber_context));
 }

Zend/zend_globals.h

@@ -62,6 +62,7 @@ END_EXTERN_C()
 typedef struct _zend_vm_stack *zend_vm_stack;
 typedef struct _zend_ini_entry zend_ini_entry;
 typedef struct _zend_fiber_context zend_fiber_context;
+typedef struct _zend_fiber zend_fiber;
 
 struct _zend_compiler_globals {
 	zend_stack loop_var_stack;
@@ -249,8 +250,11 @@ struct _zend_executor_globals {
 
 	zend_get_gc_buffer get_gc_buffer;
 
-	zend_fiber_context *main_fiber;
-	zend_fiber_context *current_fiber;
+	zend_fiber_context *main_fiber_context;
+	zend_fiber_context *current_fiber_context;
+
+	/* Active instance of Fiber. */
+	zend_fiber *active_fiber;
 
 	/* Default fiber C stack size. */
 	zend_long fiber_stack_size;

ext/reflection/php_reflection.c

@@ -6895,7 +6895,7 @@ ZEND_METHOD(ReflectionFiber, getTrace)
 	prev_execute_data = fiber->stack_bottom->prev_execute_data;
 	fiber->stack_bottom->prev_execute_data = NULL;
 
-	if (EG(current_fiber) != zend_fiber_get_context(fiber)) {
+	if (EG(active_fiber) != fiber) {
 		// No need to replace current execute data if within the current fiber.
 		EG(current_execute_data) = fiber->execute_data;
 	}
@@ -6915,7 +6915,7 @@ ZEND_METHOD(ReflectionFiber, getExecutingLine)
 
 	REFLECTION_CHECK_VALID_FIBER(fiber);
 
-	if (EG(current_fiber) == zend_fiber_get_context(fiber)) {
+	if (EG(active_fiber) == fiber) {
 		prev_execute_data = execute_data->prev_execute_data;
 	} else {
 		prev_execute_data = fiber->execute_data->prev_execute_data;
@@ -6933,7 +6933,7 @@ ZEND_METHOD(ReflectionFiber, getExecutingFile)
 
 	REFLECTION_CHECK_VALID_FIBER(fiber);
 
-	if (EG(current_fiber) == zend_fiber_get_context(fiber)) {
+	if (EG(active_fiber) == fiber) {
 		prev_execute_data = execute_data->prev_execute_data;
 	} else {
 		prev_execute_data = fiber->execute_data->prev_execute_data;

ext/zend_test/test.c

@@ -436,7 +436,7 @@ static void fiber_enter_observer(zend_fiber_context *from, zend_fiber_context *t
 	if (ZT_G(observer_fiber_switch)) {
 		if (to->status == ZEND_FIBER_STATUS_INIT) {
 			php_printf("<init '%p'>\n", to);
-		} else if (to != EG(main_fiber)) {
+		} else if (to->kind == zend_ce_fiber) {
 			zend_fiber *fiber = zend_fiber_from_context(to);
 			if (fiber->caller != from) {
 				return;
@@ -462,7 +462,7 @@ static void fiber_suspend_observer(zend_fiber_context *from, zend_fiber_context
 			} else {
 				php_printf("<returned '%p'>\n", from);
 			}
-		} else if (from != EG(main_fiber)) {
+		} else if (from->kind == zend_ce_fiber) {
 			zend_fiber *fiber = zend_fiber_from_context(from);
 			if (fiber->caller == NULL) {
 				php_printf("<suspend '%p'>\n", from);