Use a Ractor-local callback dispatcher for calls from non-ruby threads

The callback is now routet to the Ractor, that created the FFI::Function .
Within this Ractor a new ruby thread is created to execute the Proc, like before.

2 files changed, 171 insertions, 64 deletions

diff --git a/ext/ffi_c/Function.c b/ext/ffi_c/Function.c
index a74136a..f88bc93 100644
--- a/ext/ffi_c/Function.c
+++ b/ext/ffi_c/Function.c
@@ -42,6 +42,10 @@
 #include <ruby.h>
 #include <ruby/thread.h>
 
+#if HAVE_RB_EXT_RACTOR_SAFE
+#include <ruby/ractor.h>
+#endif
+
 #include <ffi.h>
 #if defined(HAVE_NATIVETHREAD) && !defined(_WIN32)
 #include <pthread.h>
@@ -65,6 +69,9 @@
 #include "MethodHandle.h"
 #include "Function.h"
 
+#define DEFER_ASYNC_CALLBACK 1
+
+struct async_cb_dispatcher;
 typedef struct Function_ {
     Pointer base;
     FunctionType* info;
@@ -73,6 +80,9 @@ typedef struct Function_ {
     Closure* closure;
     VALUE rbProc;
     VALUE rbFunctionInfo;
+#if defined(DEFER_ASYNC_CALLBACK)
+    struct async_cb_dispatcher *dispatcher;
+#endif
 } Function;
 
 static void function_mark(void *data);
@@ -86,9 +96,6 @@ static void* callback_with_gvl(void* data);
 static VALUE invoke_callback(VALUE data);
 static VALUE save_callback_exception(VALUE data, VALUE exc);
 
-#define DEFER_ASYNC_CALLBACK 1
-
-
 #if defined(DEFER_ASYNC_CALLBACK)
 static VALUE async_cb_event(void *);
 static VALUE async_cb_call(void *);
@@ -113,10 +120,6 @@ static const rb_data_type_t function_data_type = {
 
 VALUE rbffi_FunctionClass = Qnil;
 
-#if defined(DEFER_ASYNC_CALLBACK)
-static VALUE async_cb_thread = Qnil;
-#endif
-
 static ID id_call = 0, id_to_native = 0, id_from_native = 0, id_cbtable = 0, id_cb_ref = 0;
 
 struct gvl_callback {
@@ -126,7 +129,10 @@ struct gvl_callback {
     bool done;
     rbffi_frame_t *frame;
 #if defined(DEFER_ASYNC_CALLBACK)
+    struct async_cb_dispatcher *dispatcher;
     struct gvl_callback* next;
+
+    /* Signal when the callback has finished and retval is set */
 # ifndef _WIN32
     pthread_cond_t async_cond;
     pthread_mutex_t async_mutex;
@@ -138,16 +144,74 @@ struct gvl_callback {
 
 
 #if defined(DEFER_ASYNC_CALLBACK)
-static struct gvl_callback* async_cb_list = NULL;
+struct async_cb_dispatcher {
+    /* the Ractor-local dispatcher thread */
+    VALUE thread;
+
+    /* single linked list of pending callbacks */
+    struct gvl_callback* async_cb_list;
+
+    /* Signal new entries in async_cb_list */
 # ifndef _WIN32
-    static pthread_mutex_t async_cb_mutex = PTHREAD_MUTEX_INITIALIZER;
-    static pthread_cond_t async_cb_cond = PTHREAD_COND_INITIALIZER;
+    pthread_mutex_t async_cb_mutex;
+    pthread_cond_t async_cb_cond;
 # else
-    static HANDLE async_cb_cond;
-    static CRITICAL_SECTION async_cb_lock;
+    HANDLE async_cb_cond;
+    CRITICAL_SECTION async_cb_lock;
 # endif
-#endif
+};
 
+#if HAVE_RB_EXT_RACTOR_SAFE
+static void
+async_cb_dispatcher_mark(void *ptr)
+{
+    struct async_cb_dispatcher *ctx = (struct async_cb_dispatcher *)ptr;
+    rb_gc_mark(ctx->thread);
+}
+
+static void
+async_cb_dispatcher_free(void *ptr)
+{
+    struct async_cb_dispatcher *ctx = (struct async_cb_dispatcher *)ptr;
+    xfree(ctx);
+}
+
+struct rb_ractor_local_storage_type async_cb_dispatcher_key_type = {
+    async_cb_dispatcher_mark,
+    async_cb_dispatcher_free,
+};
+
+static rb_ractor_local_key_t async_cb_dispatcher_key;
+
+static struct async_cb_dispatcher *
+async_cb_dispatcher_get(void)
+{
+    struct async_cb_dispatcher *ctx = (struct async_cb_dispatcher *)rb_ractor_local_storage_ptr(async_cb_dispatcher_key);
+    return ctx;
+}
+
+static void
+async_cb_dispatcher_set(struct async_cb_dispatcher *ctx)
+{
+    rb_ractor_local_storage_ptr_set(async_cb_dispatcher_key, ctx);
+}
+#else
+// for ruby 2.x
+static struct async_cb_dispatcher *async_cb_dispatcher = NULL;
+
+static struct async_cb_dispatcher *
+async_cb_dispatcher_get(void)
+{
+    return async_cb_dispatcher;
+}
+
+static void
+async_cb_dispatcher_set(struct async_cb_dispatcher *ctx)
+{
+    async_cb_dispatcher = ctx;
+}
+#endif
+#endif
 
 static VALUE
 function_allocate(VALUE klass)
@@ -328,9 +392,7 @@ static void
 after_fork_callback(void)
 {
     /* Ensure that a new dispatcher thread is started in a forked process */
-    async_cb_thread = Qnil;
-    pthread_mutex_init(&async_cb_mutex, NULL);
-    pthread_cond_init(&async_cb_cond, NULL);
+    async_cb_dispatcher_set(NULL);
 }
 #endif
 
@@ -360,17 +422,30 @@ function_init(VALUE self, VALUE rbFunctionInfo, VALUE rbProc)
         }
 
 #if defined(DEFER_ASYNC_CALLBACK)
-        if (async_cb_thread == Qnil) {
+        {
+            struct async_cb_dispatcher *ctx = async_cb_dispatcher_get();
+            if (ctx == NULL) {
+                ctx = (struct async_cb_dispatcher*)ALLOC(struct async_cb_dispatcher);
+                ctx->async_cb_list = NULL;
 
 #if !defined(_WIN32)
-            if( pthread_atfork(NULL, NULL, after_fork_callback) ){
-                rb_warn("FFI: unable to register fork callback");
-            }
+                pthread_mutex_init(&ctx->async_cb_mutex, NULL);
+                pthread_cond_init(&ctx->async_cb_cond, NULL);
+                if( pthread_atfork(NULL, NULL, after_fork_callback) ){
+                    rb_warn("FFI: unable to register fork callback");
+                }
+#else
+                InitializeCriticalSection(&ctx->async_cb_lock);
+                ctx->async_cb_cond = CreateEvent(NULL, FALSE, FALSE, NULL);
 #endif
+                ctx->thread = rb_thread_create(async_cb_event, ctx);
 
-            async_cb_thread = rb_thread_create(async_cb_event, NULL);
-            /* Name thread, for better debugging */
-            rb_funcall(async_cb_thread, rb_intern("name="), 1, rb_str_new2("FFI Callback Dispatcher"));
+                /* Name thread, for better debugging */
+                rb_funcall(ctx->thread, rb_intern("name="), 1, rb_str_new2("FFI Callback Dispatcher"));
+
+                async_cb_dispatcher_set(ctx);
+            }
+            fn->dispatcher = ctx;
         }
 #endif
 
@@ -505,6 +580,7 @@ function_release(VALUE self)
 static void
 callback_invoke(ffi_cif* cif, void* retval, void** parameters, void* user_data)
 {
+    Function* fn;
     struct gvl_callback cb = { 0 };
 
     cb.closure = (Closure *) user_data;
@@ -512,6 +588,7 @@ callback_invoke(ffi_cif* cif, void* retval, void** parameters, void* user_data)
     cb.parameters = parameters;
     cb.done = false;
     cb.frame = rbffi_frame_current();
+    fn = (Function *) cb.closure->info;
 
     if (cb.frame != NULL) cb.frame->exc = Qnil;
 
@@ -524,18 +601,19 @@ callback_invoke(ffi_cif* cif, void* retval, void** parameters, void* user_data)
 #if defined(DEFER_ASYNC_CALLBACK) && !defined(_WIN32)
     } else {
         bool empty = false;
+        struct async_cb_dispatcher *ctx = fn->dispatcher;
 
         pthread_mutex_init(&cb.async_mutex, NULL);
         pthread_cond_init(&cb.async_cond, NULL);
 
-        /* Now signal the async callback thread */
-        pthread_mutex_lock(&async_cb_mutex);
-        empty = async_cb_list == NULL;
-        cb.next = async_cb_list;
-        async_cb_list = &cb;
+        /* Now signal the async callback dispatcher thread */
+        pthread_mutex_lock(&ctx->async_cb_mutex);
+        empty = ctx->async_cb_list == NULL;
+        cb.next = ctx->async_cb_list;
+        ctx->async_cb_list = &cb;
 
-        pthread_cond_signal(&async_cb_cond);
-        pthread_mutex_unlock(&async_cb_mutex);
+        pthread_cond_signal(&ctx->async_cb_cond);
+        pthread_mutex_unlock(&ctx->async_cb_mutex);
 
         /* Wait for the thread executing the ruby callback to signal it is done */
         pthread_mutex_lock(&cb.async_mutex);
@@ -549,17 +627,18 @@ callback_invoke(ffi_cif* cif, void* retval, void** parameters, void* user_data)
 #elif defined(DEFER_ASYNC_CALLBACK) && defined(_WIN32)
     } else {
         bool empty = false;
+        struct async_cb_dispatcher *ctx = fn->dispatcher;
 
         cb.async_event = CreateEvent(NULL, FALSE, FALSE, NULL);
 
-        /* Now signal the async callback thread */
-        EnterCriticalSection(&async_cb_lock);
-        empty = async_cb_list == NULL;
-        cb.next = async_cb_list;
-        async_cb_list = &cb;
-        LeaveCriticalSection(&async_cb_lock);
+        /* Now signal the async callback dispatcher thread */
+        EnterCriticalSection(&ctx->async_cb_lock);
+        empty = ctx->async_cb_list == NULL;
+        cb.next = ctx->async_cb_list;
+        ctx->async_cb_list = &cb;
+        LeaveCriticalSection(&ctx->async_cb_lock);
 
-        SetEvent(async_cb_cond);
+        SetEvent(ctx->async_cb_cond);
 
         /* Wait for the thread executing the ruby callback to signal it is done */
         WaitForSingleObject(cb.async_event, INFINITE);
@@ -570,6 +649,7 @@ callback_invoke(ffi_cif* cif, void* retval, void** parameters, void* user_data)
 
 #if defined(DEFER_ASYNC_CALLBACK)
 struct async_wait {
+    struct async_cb_dispatcher *dispatcher;
     void* cb;
     bool stop;
 };
@@ -578,9 +658,10 @@ static void * async_cb_wait(void *);
 static void async_cb_stop(void *);
 
 static VALUE
-async_cb_event(void* unused)
+async_cb_event(void* ptr)
 {
-    struct async_wait w = { 0 };
+    struct async_cb_dispatcher *ctx = (struct async_cb_dispatcher *)ptr;
+    struct async_wait w = { ctx };
 
     w.stop = false;
     while (!w.stop) {
@@ -601,23 +682,24 @@ static void *
 async_cb_wait(void *data)
 {
     struct async_wait* w = (struct async_wait *) data;
+    struct async_cb_dispatcher *ctx = w->dispatcher;
 
     w->cb = NULL;
 
-    EnterCriticalSection(&async_cb_lock);
+    EnterCriticalSection(&ctx->async_cb_lock);
 
-    while (!w->stop && async_cb_list == NULL) {
-        LeaveCriticalSection(&async_cb_lock);
-        WaitForSingleObject(async_cb_cond, INFINITE);
-        EnterCriticalSection(&async_cb_lock);
+    while (!w->stop && ctx->async_cb_list == NULL) {
+        LeaveCriticalSection(&ctx->async_cb_lock);
+        WaitForSingleObject(ctx->async_cb_cond, INFINITE);
+        EnterCriticalSection(&ctx->async_cb_lock);
     }
 
-    if (async_cb_list != NULL) {
-        w->cb = async_cb_list;
-        async_cb_list = async_cb_list->next;
+    if (ctx->async_cb_list != NULL) {
+        w->cb = ctx->async_cb_list;
+        ctx->async_cb_list = ctx->async_cb_list->next;
     }
 
-    LeaveCriticalSection(&async_cb_lock);
+    LeaveCriticalSection(&ctx->async_cb_lock);
 
     return NULL;
 }
@@ -626,11 +708,12 @@ static void
 async_cb_stop(void *data)
 {
     struct async_wait* w = (struct async_wait *) data;
+    struct async_cb_dispatcher *ctx = w->dispatcher;
 
-    EnterCriticalSection(&async_cb_lock);
+    EnterCriticalSection(&ctx->async_cb_lock);
     w->stop = true;
-    LeaveCriticalSection(&async_cb_lock);
-    SetEvent(async_cb_cond);
+    LeaveCriticalSection(&ctx->async_cb_lock);
+    SetEvent(ctx->async_cb_cond);
 }
 
 #else
@@ -638,21 +721,22 @@ static void *
 async_cb_wait(void *data)
 {
     struct async_wait* w = (struct async_wait *) data;
+    struct async_cb_dispatcher *ctx = w->dispatcher;
 
     w->cb = NULL;
 
-    pthread_mutex_lock(&async_cb_mutex);
+    pthread_mutex_lock(&ctx->async_cb_mutex);
 
-    while (!w->stop && async_cb_list == NULL) {
-        pthread_cond_wait(&async_cb_cond, &async_cb_mutex);
+    while (!w->stop && ctx->async_cb_list == NULL) {
+        pthread_cond_wait(&ctx->async_cb_cond, &ctx->async_cb_mutex);
     }
 
-    if (async_cb_list != NULL) {
-        w->cb = async_cb_list;
-        async_cb_list = async_cb_list->next;
+    if (ctx->async_cb_list != NULL) {
+        w->cb = ctx->async_cb_list;
+        ctx->async_cb_list = ctx->async_cb_list->next;
     }
 
-    pthread_mutex_unlock(&async_cb_mutex);
+    pthread_mutex_unlock(&ctx->async_cb_mutex);
 
     return NULL;
 }
@@ -661,11 +745,12 @@ static void
 async_cb_stop(void *data)
 {
     struct async_wait* w = (struct async_wait *) data;
+    struct async_cb_dispatcher *ctx = w->dispatcher;
 
-    pthread_mutex_lock(&async_cb_mutex);
+    pthread_mutex_lock(&ctx->async_cb_mutex);
     w->stop = true;
-    pthread_cond_signal(&async_cb_cond);
-    pthread_mutex_unlock(&async_cb_mutex);
+    pthread_cond_signal(&ctx->async_cb_cond);
+    pthread_mutex_unlock(&ctx->async_cb_mutex);
 }
 #endif
 
@@ -961,8 +1046,7 @@ rbffi_Function_Init(VALUE moduleFFI)
     id_cb_ref = rb_intern("@__ffi_callback__");
     id_to_native = rb_intern("to_native");
     id_from_native = rb_intern("from_native");
-#if defined(_WIN32)
-    InitializeCriticalSection(&async_cb_lock);
-    async_cb_cond = CreateEvent(NULL, FALSE, FALSE, NULL);
+#if defined(DEFER_ASYNC_CALLBACK) && defined(HAVE_RB_EXT_RACTOR_SAFE)
+    async_cb_dispatcher_key = rb_ractor_local_storage_ptr_newkey(&async_cb_dispatcher_key_type);
 #endif
 }
diff --git a/spec/ffi/async_callback_spec.rb b/spec/ffi/async_callback_spec.rb
index 51a4886..7bb9f70 100644
--- a/spec/ffi/async_callback_spec.rb
+++ b/spec/ffi/async_callback_spec.rb
@@ -50,4 +50,27 @@ describe "async callback" do
 
     expect(callback_runner_thread.name).to eq("FFI Callback Runner")
   end
+
+  it "works in Ractor", :ractor do
+    skip "not yet supported on TruffleRuby" if RUBY_ENGINE == "truffleruby"
+
+    res = Ractor.new do
+      v = 0xdeadbeef
+      correct_ractor = false
+      correct_thread = false
+      thread = Thread.current
+      rac = Ractor.current
+      cb = Proc.new do |i|
+        v = i
+        correct_ractor = rac == Ractor.current
+        correct_thread = thread != Thread.current
+      end
+      LibTest.testAsyncCallback(cb, 0x7fffffff)
+
+      [v, correct_ractor, correct_thread]
+    end.take
+
+    expect(res).to eq([0x7fffffff, true, true])
+  end
+
 end