Make FFI callbacks thread safe

ext/ffi/ffi.c

@@ -935,9 +935,24 @@ static void zend_ffi_callback_hash_dtor(zval *zv) /* {{{ */
 }
 /* }}} */
 
-static void zend_ffi_callback_trampoline(ffi_cif* cif, void* ret, void** args, void* data) /* {{{ */
-{
-	zend_ffi_callback_data *callback_data = (zend_ffi_callback_data*)data;
+static void (*orig_interrupt_function)(zend_execute_data *execute_data);
+
+static void zend_ffi_dispatch_callback_end(void){ /* {{{ */
+	zend_atomic_bool_store_ex(&FFI_G(callback_in_progress), false);
+	pthread_cond_broadcast(&FFI_G(vm_ack));
+	pthread_mutex_unlock(&FFI_G(vm_lock));
+}
+/* }}} */
+
+static void zend_ffi_dispatch_callback(void){ /* {{{ */
+	// this function must always run on the main thread
+	assert(pthread_self() == FFI_G(main_tid));
+
+	if (!zend_atomic_bool_load_ex(&FFI_G(callback_in_progress))) {
+		return;
+	}
+
+	zend_ffi_callback_data *callback_data = FFI_G(callback_data).data;
 	zend_fcall_info fci;
 	zend_ffi_type *ret_type;
 	zval retval;
@@ -951,13 +966,14 @@ static void zend_ffi_callback_trampoline(ffi_cif* cif, void* ret, void** args, v
 	fci.param_count = callback_data->arg_count;
 	fci.named_params = NULL;
 
+
 	if (callback_data->type->func.args) {
 		int n = 0;
 		zend_ffi_type *arg_type;
 
 		ZEND_HASH_PACKED_FOREACH_PTR(callback_data->type->func.args, arg_type) {
 			arg_type = ZEND_FFI_TYPE(arg_type);
-			zend_ffi_cdata_to_zval(NULL, args[n], arg_type, BP_VAR_R, &fci.params[n], (zend_ffi_flags)(arg_type->attr & ZEND_FFI_ATTR_CONST), 0, 0);
+			zend_ffi_cdata_to_zval(NULL, FFI_G(callback_data).args[n], arg_type, BP_VAR_R, &fci.params[n], (zend_ffi_flags)(arg_type->attr & ZEND_FFI_ATTR_CONST), 0, 0);
 			n++;
 		} ZEND_HASH_FOREACH_END();
 	}
@@ -977,15 +993,77 @@ static void zend_ffi_callback_trampoline(ffi_cif* cif, void* ret, void** args, v
 	free_alloca(fci.params, use_heap);
 
 	if (EG(exception)) {
+		zend_ffi_dispatch_callback_end();
 		zend_error_noreturn(E_ERROR, "Throwing from FFI callbacks is not allowed");
 	}
 
 	ret_type = ZEND_FFI_TYPE(callback_data->type->func.ret_type);
 	if (ret_type->kind != ZEND_FFI_TYPE_VOID) {
-		zend_ffi_zval_to_cdata(ret, ret_type, &retval);
+		zend_ffi_zval_to_cdata(FFI_G(callback_data).ret, ret_type, &retval);
 	}
 
 	zval_ptr_dtor(&retval);
+	zend_ffi_dispatch_callback_end();
+}
+/* }}} */
+
+static void zend_ffi_interrupt_function(zend_execute_data *execute_data){ /* {{{ */
+	zend_ffi_dispatch_callback();
+
+	if (orig_interrupt_function) {
+		orig_interrupt_function(execute_data);
+	}
+}
+/* }}} */
+
+static void zend_ffi_wait_request_barrier(bool release){ /* {{{ */
+	// get lock, first
+	pthread_mutex_lock(&FFI_G(vm_lock));
+
+	while(zend_atomic_bool_load_ex(&FFI_G(callback_in_progress))){
+		// we acquired the lock before the request could be serviced
+		// unlock it and wait for the flag
+		pthread_cond_wait(&FFI_G(vm_ack), &FFI_G(vm_lock));
+	}
+
+	if(release){
+		pthread_mutex_unlock(&FFI_G(vm_lock));
+	}
+}
+/* }}} */
+
+static void zend_ffi_callback_trampoline(ffi_cif* cif, void* ret, void** args, void* data) /* {{{ */
+{
+	// wait for a previously initiated request to complete
+	zend_ffi_wait_request_barrier(false);
+
+	// mutex is now locked, and request is not pending.
+	// start a new one
+	zend_atomic_bool_store_ex(&FFI_G(callback_in_progress), true);
+
+	zend_ffi_call_data call_data = {
+		.cif = cif,
+		.ret = ret,
+		.args = args,
+		.data = (zend_ffi_callback_data *)data
+	};
+	FFI_G(callback_data) = call_data;
+
+	bool is_main_thread = pthread_self() == FFI_G(main_tid);
+
+	if(is_main_thread){
+		// dispatch the callback directly
+		zend_ffi_dispatch_callback();
+	} else {
+		// post interrupt request to acquire the main thread
+		zend_atomic_bool_store_ex(&EG(vm_interrupt), true);
+		pthread_mutex_unlock(&FFI_G(vm_lock));
+	}
+
+	if(!is_main_thread){
+		// wait for the request to complete before returning
+		zend_ffi_wait_request_barrier(true);
+	}
 }
 /* }}} */
 
@@ -5518,13 +5596,24 @@ ZEND_MINIT_FUNCTION(ffi)
 		return zend_ffi_preload(FFI_G(preload));
 	}
 
+	FFI_G(main_tid) = pthread_self();
+
+	zend_atomic_bool_store_ex(&FFI_G(callback_in_progress), false);
+	orig_interrupt_function = zend_interrupt_function;
+	zend_interrupt_function = zend_ffi_interrupt_function;
+
+	pthread_mutex_init(&FFI_G(vm_lock), NULL);
+	pthread_cond_init(&FFI_G(vm_ack), NULL);
+
 	return SUCCESS;
 }
 /* }}} */
 
 /* {{{ ZEND_RSHUTDOWN_FUNCTION */
 ZEND_RSHUTDOWN_FUNCTION(ffi)
 {
+	zend_ffi_wait_request_barrier(true);
+
 	if (FFI_G(callbacks)) {
 		zend_hash_destroy(FFI_G(callbacks));
 		efree(FFI_G(callbacks));
@@ -5636,6 +5725,7 @@ static ZEND_GINIT_FUNCTION(ffi)
 /* {{{ ZEND_GINIT_FUNCTION */
 static ZEND_GSHUTDOWN_FUNCTION(ffi)
 {
+	zend_ffi_wait_request_barrier(true);
 	if (ffi_globals->scopes) {
 		zend_hash_destroy(ffi_globals->scopes);
 		free(ffi_globals->scopes);

ext/ffi/php_ffi.h

@@ -17,6 +17,9 @@
 #ifndef PHP_FFI_H
 #define PHP_FFI_H
 
+#include <ffi.h>
+#include <pthread.h>
+
 extern zend_module_entry ffi_module_entry;
 #define phpext_ffi_ptr &ffi_module_entry
 
@@ -27,6 +30,15 @@ typedef enum _zend_ffi_api_restriction {
 } zend_ffi_api_restriction;
 
 typedef struct _zend_ffi_type  zend_ffi_type;
+typedef struct _zend_ffi_callback_data zend_ffi_callback_data;
+
+
+typedef struct _zend_ffi_call_data {
+	ffi_cif* cif;
+	void* ret;
+	void** args;
+	zend_ffi_callback_data* data;
+} zend_ffi_call_data;
 
 ZEND_BEGIN_MODULE_GLOBALS(ffi)
 	zend_ffi_api_restriction restriction;
@@ -35,6 +47,12 @@ ZEND_BEGIN_MODULE_GLOBALS(ffi)
 	/* predefined ffi_types */
 	HashTable types;
 
+	zend_atomic_bool callback_in_progress;
+	pthread_mutex_t vm_lock;
+	pthread_cond_t vm_ack;
+	pthread_t main_tid;
+	zend_ffi_call_data callback_data;
+
 	/* preloading */
 	char *preload;
 	HashTable *scopes;           /* list of preloaded scopes */

ext/ffi/tests/callback_threads.phpt

@@ -0,0 +1,59 @@
+--TEST--
+FFI Thread safe callbacks
+--EXTENSIONS--
+ffi
+--SKIPIF--
+<?php
+try {
+	$libc = FFI::cdef('
+		int pthread_create(void *restrict thread,
+							const void *restrict attr,
+							void *(*start_routine)(void *),
+							void *arg);
+		', 'libc.so.6');
+} catch(Throwable $_){
+	die('skip libc.so.6 not available');
+}
+?>
+--INI--
+ffi.enable=1
+--FILE--
+<?php
+$libc = FFI::cdef('
+typedef uint64_t pthread_t;
+int pthread_create(pthread_t *thread,
+					const void* attr,
+					void *(*start_routine)(void *),
+					void *arg);
+int pthread_detach(pthread_t thread);
+', 'libc.so.6');
+
+$tid = $libc->new($libc->type('pthread_t'));
+$accum = 0;
+$thread_func = function($arg) use($libc, &$accum){
+	//$v = $libc->cast('int *', $arg)[0];
+	FFI::free($arg);
+	usleep(10 * 1000);
+	$accum++;
+	//print(".");
+};
+
+for($i=0; $i<100; $i++){
+	$arg = $libc->new('int', false);
+	$arg->cdata = $i;
+
+	$libc->pthread_create(
+		FFI::addr($tid), NULL,
+		$thread_func, FFI::addr($arg)
+	);
+	$libc->pthread_detach($tid->cdata);
+}
+
+while($accum != 100){
+	//print("w");
+	usleep(1000);
+}
+print($accum);
+?>
+--EXPECT--
+100