Fiber ucontext support

Author: trowski

Zend/zend_fibers.c

@@ -113,6 +113,9 @@ static zend_always_inline void zend_fiber_restore_vm_state(zend_fiber_vm_state *
 	EG(active_fiber) = state->active_fiber;
 }
 
+#ifdef ZEND_FIBER_UCONTEXT
+# include <ucontext.h>
+#else
 /* boost_context_data is our customized definition of struct transfer_t as
  * provided by boost.context in fcontext.hpp:
  *
@@ -125,12 +128,13 @@ static zend_always_inline void zend_fiber_restore_vm_state(zend_fiber_vm_state *
 
 typedef struct {
 	void *handle;
-	zend_fiber_transfer *transfer;
+	zend_fiber_context *context;
 } boost_context_data;
 
 /* These functions are defined in assembler files provided by boost.context (located in "Zend/asm"). */
 extern void *make_fcontext(void *sp, size_t size, void (*fn)(boost_context_data));
-extern boost_context_data jump_fcontext(void *to, zend_fiber_transfer *data);
+extern boost_context_data jump_fcontext(void *to, zend_fiber_context *context);
+#endif
 
 ZEND_API zend_class_entry *zend_ce_fiber;
 static zend_class_entry *zend_ce_fiber_error;
@@ -245,27 +249,21 @@ static void zend_fiber_stack_free(zend_fiber_stack *stack)
 	efree(stack);
 }
 
-static ZEND_NORETURN void zend_fiber_trampoline(boost_context_data data)
+static ZEND_NORETURN void zend_fiber_trampoline(zend_fiber_context *context)
 {
-	zend_fiber_context *from = data.transfer->context;
+	/* Initialize transfer struct with a copy of passed data. */
+	zend_fiber_transfer transfer = *context->transfer;
+	zend_fiber_context *from = transfer.context;
 
 #ifdef __SANITIZE_ADDRESS__
 	__sanitizer_finish_switch_fiber(NULL, &from->stack->asan_pointer, &from->stack->asan_size);
 #endif
 
-	/* Get a hold of the context that resumed us and update its handle to allow for symmetric coroutines. */
-	from->handle = data.handle;
-
-	/* Initialize transfer struct with a copy of passed data. */
-	zend_fiber_transfer transfer = *data.transfer;
-
 	/* Ensure that previous fiber will be cleaned up (needed by symmetric coroutines). */
 	if (from->status == ZEND_FIBER_STATUS_DEAD) {
 		zend_fiber_destroy_context(from);
 	}
 
-	zend_fiber_context *context = EG(current_fiber_context);
-
 	context->function(&transfer);
 	context->status = ZEND_FIBER_STATUS_DEAD;
 
@@ -276,6 +274,19 @@ static ZEND_NORETURN void zend_fiber_trampoline(boost_context_data data)
 	abort();
 }
 
+#ifndef ZEND_FIBER_UCONTEXT
+static ZEND_NORETURN void zend_fiber_start(boost_context_data data)
+{
+	zend_fiber_context *context = data.context;
+
+	/* Get the context that resumed us and update its handle to allow for symmetric coroutines. */
+	zend_fiber_context *from = context->transfer->context;
+	from->handle = data.handle;
+
+	zend_fiber_trampoline(context);
+}
+#endif
+
 ZEND_API void zend_fiber_switch_block(void)
 {
 	++zend_fiber_switch_blocking;
@@ -300,11 +311,25 @@ ZEND_API bool zend_fiber_init_context(zend_fiber_context *context, void *kind, z
 		return false;
 	}
 
+#ifdef ZEND_FIBER_UCONTEXT
+	ucontext_t *handle = emalloc(sizeof(ucontext_t));
+	getcontext(handle);
+
+	handle->uc_stack.ss_size = context->stack->size;
+	handle->uc_stack.ss_sp = context->stack->pointer;
+	handle->uc_stack.ss_flags = 0;
+	handle->uc_link = NULL;
+
+	makecontext(handle, (void (*)(void)) zend_fiber_trampoline, 1, context);
+
+	context->handle = handle;
+#else
 	// Stack grows down, calculate the top of the stack. make_fcontext then shifts pointer to lower 16-byte boundary.
 	void *stack = (void *) ((uintptr_t) context->stack->pointer + context->stack->size);
 
-	context->handle = make_fcontext(stack, context->stack->size, zend_fiber_trampoline);
+	context->handle = make_fcontext(stack, context->stack->size, zend_fiber_start);
 	ZEND_ASSERT(context->handle != NULL && "make_fcontext() never returns NULL");
+#endif
 
 	context->kind = kind;
 	context->function = coroutine;
@@ -318,6 +343,10 @@ ZEND_API bool zend_fiber_init_context(zend_fiber_context *context, void *kind, z
 ZEND_API void zend_fiber_destroy_context(zend_fiber_context *context)
 {
 	zend_fiber_stack_free(context->stack);
+
+#ifdef ZEND_FIBER_UCONTEXT
+	efree(context->handle);
+#endif
 }
 
 ZEND_API void zend_fiber_switch_context(zend_fiber_transfer *transfer)
@@ -352,6 +381,7 @@ ZEND_API void zend_fiber_switch_context(zend_fiber_transfer *transfer)
 
 	/* Update transfer context with the current fiber before switching. */
 	transfer->context = from;
+	to->transfer = transfer;
 
 	EG(current_fiber_context) = to;
 
@@ -363,14 +393,20 @@ ZEND_API void zend_fiber_switch_context(zend_fiber_transfer *transfer)
 		to->stack->asan_size);
 #endif
 
-	boost_context_data data = jump_fcontext(to->handle, transfer);
+#ifdef ZEND_FIBER_UCONTEXT
+	swapcontext(from->handle, to->handle);
+#else
+	boost_context_data data = jump_fcontext(to->handle, to);
+#endif
 
 	/* Copy transfer struct because it might live on the other fiber's stack that will eventually be destroyed. */
-	*transfer = *data.transfer;
+	*transfer = *from->transfer;
 
-	/* Get a hold of the context that resumed us and update its handle to allow for symmetric coroutines. */
+	/* Get the context that resumed us and update its handle to allow for symmetric coroutines. */
 	to = transfer->context;
+#ifndef ZEND_FIBER_UCONTEXT
 	to->handle = data.handle;
+#endif
 
 #ifdef __SANITIZE_ADDRESS__
 	__sanitizer_finish_switch_fiber(fake_stack, &to->stack->asan_pointer, &to->stack->asan_size);
@@ -844,6 +880,10 @@ void zend_fiber_init(void)
 	context->stack = emalloc(sizeof(zend_fiber_stack));
 #endif
 
+#ifdef ZEND_FIBER_UCONTEXT
+	context->handle = emalloc(sizeof(ucontext_t));
+#endif
+
 	context->status = ZEND_FIBER_STATUS_RUNNING;
 
 	EG(main_fiber_context) = context;
@@ -855,9 +895,14 @@ void zend_fiber_init(void)
 
 void zend_fiber_shutdown(void)
 {
+#ifdef ZEND_FIBER_UCONTEXT
+	efree(EG(main_fiber_context)->handle);
+#endif
+
 #ifdef __SANITIZE_ADDRESS__
 	efree(EG(main_fiber_context)->stack);
 #endif
+
 	efree(EG(main_fiber_context));
 
 	zend_fiber_switch_block();

Zend/zend_fibers.h

@@ -73,7 +73,7 @@ typedef struct _zend_fiber_transfer {
 typedef void (*zend_fiber_coroutine)(zend_fiber_transfer *transfer);
 
 struct _zend_fiber_context {
-	/* Handle to fiber state as needed by boost.context */
+	/* Pointer to boost.context or ucontext_t data. */
 	void *handle;
 
 	/* Pointer that identifies the fiber type. */
@@ -82,6 +82,9 @@ struct _zend_fiber_context {
 	/* Entrypoint function of the fiber. */
 	zend_fiber_coroutine function;
 
+	/* Data transferred from calling context. */
+	zend_fiber_transfer *transfer;
+
 	/* Assigned C stack. */
 	zend_fiber_stack *stack;
 

configure.ac

@@ -1192,8 +1192,14 @@ dnl ----------------------------------------------------------------------------
 PHP_HELP_SEPARATOR([Zend:])
 PHP_CONFIGURE_PART(Configuring Zend)
 
+fiber_asm="yes"
+fiber_ucontext="no"
+
+AC_CHECK_HEADER(ucontext.h, [
+  fiber_ucontext="yes"
+])
+
 AC_MSG_CHECKING(for fiber switching context)
-fibers="yes"
 
 AS_CASE([$host_cpu],
   [x86_64*|amd64*], [fiber_cpu="x86_64"],
@@ -1231,14 +1237,18 @@ if test "$fiber_os" = 'mac'; then
 elif test "$fiber_asm_file_prefix" != 'unknown'; then
   fiber_asm_file="${fiber_asm_file_prefix}_elf_gas"
 else
-  fibers="no"
+  fiber_asm="no"
 fi
 
-if test "$fibers" = 'yes'; then
+if test "$fiber_asm" = 'yes'; then
+  AC_DEFINE([ZEND_FIBER_ASM], 1, [ ])
   PHP_ADD_SOURCES(Zend/asm, make_${fiber_asm_file}.S jump_${fiber_asm_file}.S)
   AC_MSG_RESULT([$fiber_asm_file])
+elif test "$fiber_ucontext" = 'yes'; then
+  AC_DEFINE([ZEND_FIBER_UCONTEXT], 1, [ ])
+  AC_MSG_RESULT([ucontext.h])
 else
-  AC_MSG_ERROR([Unable to determine platform!])
+  AC_MSG_ERROR([No fiber switching context available on this platform])
 fi
 
 LIBZEND_BASIC_CHECKS