From 1cfbd6226690ad9a808e40c5a8d4c5e03eac9d5f Mon Sep 17 00:00:00 2001
From: ridiculousfish <corydoras@ridiculousfish.com>
Date: Mon, 23 Jan 2017 11:35:22 -0800
Subject: [PATCH] Enable use of std::function and lambdas in iothread_perform

---
 src/iothread.cpp | 52 ++++++++++++++++++++++++------------------------
 src/iothread.h   | 28 +++++++++++++++++---------
 2 files changed, 45 insertions(+), 35 deletions(-)

diff --git a/src/iothread.cpp b/src/iothread.cpp
index d3cff9a70..0ed6f52b1 100644
--- a/src/iothread.cpp
+++ b/src/iothread.cpp
@@ -33,13 +33,19 @@
 static void iothread_service_main_thread_requests(void);
 static void iothread_service_result_queue();
 
-struct spawn_request_t {
-    int (*handler)(void *) = NULL;
-    void (*completion)(void *, int) = NULL;
-    void *context = NULL;
-    int handler_result = -1;
+typedef std::function<void(void)> void_function_t;
 
-    spawn_request_t() {}
+struct spawn_request_t {
+    void_function_t handler;
+    void_function_t completion;
+
+    spawn_request_t()
+    {}
+
+    spawn_request_t(void_function_t f, void_function_t comp) :
+        handler(std::move(f)),
+        completion(std::move(comp))
+    {}
 
     // Move-only
     spawn_request_t &operator=(const spawn_request_t &) = delete;
@@ -50,9 +56,9 @@ struct spawn_request_t {
 
 struct main_thread_request_t {
     volatile bool done = false;
-    std::function<void(void)> func;
+    void_function_t func;
 
-    main_thread_request_t(std::function<void(void)> &&f) : func(f) {}
+    main_thread_request_t(void_function_t f) : func(std::move(f)) {}
 
     // No moving OR copying
     // main_thread_requests are always stack allocated, and we deal in pointers to them
@@ -131,10 +137,11 @@ static void *iothread_worker(void *unused) {
         locker.unlock();
 
         // Perform the work.
-        req.handler_result = req.handler(req.context);
+        req.handler();
 
         // If there's a completion handler, we have to enqueue it on the result queue.
-        if (req.completion != NULL) {
+        // Note we're using std::function's weirdo operator== here
+        if (req.completion != nullptr) {
             // Enqueue the result, and tell the main thread about it.
             enqueue_thread_result(std::move(req));
             const char wakeup_byte = IO_SERVICE_RESULT_QUEUE;
@@ -183,23 +190,17 @@ static void iothread_spawn() {
     VOMIT_ON_FAILURE(pthread_sigmask(SIG_SETMASK, &saved_set, NULL));
 }
 
-int iothread_perform_base(int (*handler)(void *), void (*completion)(void *, int),
-                          void *context) {
+int iothread_perform(void_function_t &&func, void_function_t &&completion) {
     ASSERT_IS_MAIN_THREAD();
     ASSERT_IS_NOT_FORKED_CHILD();
     iothread_init();
-
-    // Create and initialize a request.
-    struct spawn_request_t req;
-    req.handler = handler;
-    req.completion = completion;
-    req.context = context;
-
+    
+    struct spawn_request_t req(std::move(func), std::move(completion));
     int local_thread_count = -1;
     bool spawn_new_thread = false;
     {
-        // Lock around a local region. Note that we can only access s_active_thread_count under the
-        // lock.
+        // Lock around a local region.
+        // Note that we can only access s_active_thread_count under the lock.
         scoped_lock locker(s_spawn_queue_lock);
         add_to_queue(std::move(req));
         if (s_active_thread_count < IO_MAX_THREADS) {
@@ -213,8 +214,6 @@ int iothread_perform_base(int (*handler)(void *), void (*completion)(void *, int
     if (spawn_new_thread) {
         iothread_spawn();
     }
-
-    // We return the active thread count for informational purposes only.
     return local_thread_count;
 }
 
@@ -334,13 +333,14 @@ static void iothread_service_result_queue() {
     while (!result_queue.empty()) {
         spawn_request_t req = std::move(result_queue.front());
         result_queue.pop();
-        if (req.completion) {
-            req.completion(req.context, req.handler_result);
+        // ensure we don't invoke empty functions, that raises an exception
+        if (req.completion != nullptr) {
+            req.completion();
         }
     }
 }
 
-void iothread_perform_on_main(std::function<void(void)> &&func) {
+void iothread_perform_on_main(void_function_t &&func) {
     if (is_main_thread()) {
         func();
         return;
diff --git a/src/iothread.h b/src/iothread.h
index e5383781b..5faa477e7 100644
--- a/src/iothread.h
+++ b/src/iothread.h
@@ -26,19 +26,29 @@ void iothread_service_completion(void);
 /// Waits for all iothreads to terminate.
 void iothread_drain_all(void);
 
-/// Helper templates.
-template <typename T>
-int iothread_perform(int (*handler)(T *), void (*completion)(T *, int), T *context) {
-    return iothread_perform_base((int (*)(void *))handler,
-                                 (void (*)(void *, int))completion,
-                                 static_cast<void *>(context));
+int iothread_perform(std::function<void(void)> &&func,
+                     std::function<void(void)> &&completion = std::function<void(void)>());
+
+// Variant that allows computing a value in func, and then passing it to the completion handler
+template<typename T>
+int iothread_perform(std::function<T(void)> &&handler, std::function<void(T)> &&completion) {
+    T *result = new T();
+    return iothread_perform([=](){ *result = handler(); },
+                            [=](){ completion(std::move(*result)); delete result; }
+                            );
+}
+
+/// Legacy templates
+template <typename T>
+int iothread_perform(int (*handler)(T *), void (*completion)(T *, int), T *context) {
+    return iothread_perform(std::function<int(void)>([=](){return handler(context);}),
+                            std::function<void(int)>([=](int v){completion(context, v);})
+                            );
 }
 
-// Variant that takes no completion callback.
 template <typename T>
 int iothread_perform(int (*handler)(T *), T *context) {
-    return iothread_perform_base((int (*)(void *))handler, (void (*)(void *, int))0,
-                                 static_cast<void *>(context));
+    return iothread_perform([=](){ handler(context); });
 }
 
 /// Performs a function on the main thread, blocking until it completes.