Use fd_event_signaller in iothread completions

This simplifies how iothread notices when there are completions ready to
run.

src/fish_tests.cpp

@@ -971,7 +971,7 @@ static void test_debounce() {
 
     // Wait until the last completion is done.
     while (!completion_ran.back()) {
-        iothread_service_completion();
+        iothread_service_main();
     }
     iothread_drain_all();
 

src/input_common.cpp

@@ -124,7 +124,7 @@ char_event_t input_event_queue_t::readb() {
             // Check for iothread completions only if there is no data to be read from the stdin.
             // This gives priority to the foreground.
             if (ioport > 0 && FD_ISSET(ioport, &fdset)) {
-                iothread_service_completion();
+                iothread_service_main();
                 if (auto mc = pop_discard_timeouts()) {
                     return *mc;
                 }

src/iothread.cpp

@@ -31,16 +31,9 @@
 // which is too low, even tho the system can handle more than 64 threads.
 #define IO_MAX_THREADS 1024
 
-// Values for the wakeup bytes sent to the ioport.
-#define IO_SERVICE_MAIN_THREAD_REQUEST_QUEUE 99
-#define IO_SERVICE_RESULT_QUEUE 100
-
 // The amount of time an IO thread many hang around to service requests, in milliseconds.
 #define IO_WAIT_FOR_WORK_DURATION_MS 500
 
-static void iothread_service_main_thread_requests();
-static void iothread_service_result_queue();
-
 using void_function_t = std::function<void()>;
 
 struct work_request_t {
@@ -140,32 +133,38 @@ struct thread_pool_t {
 /// Leaked to avoid shutdown dtor registration (including tsan).
 static thread_pool_t &s_io_thread_pool = *(new thread_pool_t(1, IO_MAX_THREADS));
 
-static owning_lock<std::vector<void_function_t>> s_result_queue;
+/// A queue of "things to do on the main thread."
+struct main_thread_queue_t {
+    // Functions to invoke as the completion callback from iothread_perform.
+    std::vector<void_function_t> completions;
 
-// "Do on main thread" support.
-// The queue of main thread requests. This queue contains pointers to structs that are
-// stack-allocated on the requesting thread.
-static owning_lock<std::vector<main_thread_request_t *>> s_main_thread_request_queue;
+    // iothread_perform_on_main requests.
+    // Note this contains pointers to structs that are stack-allocated on the requesting thread.
+    std::vector<main_thread_request_t *> requests;
 
-// Pipes used for notifying.
-struct notify_pipes_t {
-    int read;
-    int write;
-};
-
-/// \return the (immortal) set of pipes used for notifying of completions.
-static const notify_pipes_t &get_notify_pipes() {
-    static const notify_pipes_t s_notify_pipes = [] {
-        auto pipes = make_autoclose_pipes();
-        if (!pipes) {
-            DIE_WITH_ERRNO("Unable to create iothread notify pipes");
+    /// Transfer ownership of ourselves to a new queue and return it.
+    /// 'this' is left empty.
+    main_thread_queue_t take() {
+        main_thread_queue_t result;
+        std::swap(result.completions, this->completions);
+        std::swap(result.requests, this->requests);
+        return result;
     }
-        // Mark both ends as non-blocking.
-        if (make_fd_nonblocking(pipes->read.fd())) wperror(L"fcntl");
-        if (make_fd_nonblocking(pipes->write.fd())) wperror(L"fcntl");
-        return notify_pipes_t{pipes->read.acquire(), pipes->write.acquire()};
-    }();
-    return s_notify_pipes;
+
+    // Moving is allowed, but not copying.
+    main_thread_queue_t() = default;
+    main_thread_queue_t(main_thread_queue_t &&) = default;
+    main_thread_queue_t &operator=(main_thread_queue_t &&) = default;
+    main_thread_queue_t(const main_thread_queue_t &) = delete;
+    void operator=(const main_thread_queue_t &) = delete;
+};
+static owning_lock<main_thread_queue_t> s_main_thread_queue;
+
+/// \return the signaller for completions and main thread requests.
+static fd_event_signaller_t &get_notify_signaller() {
+    // Leaked to avoid shutdown dtors.
+    static fd_event_signaller_t *s_signaller = new fd_event_signaller_t();
+    return *s_signaller;
 }
 
 /// Dequeue a work item (perhaps waiting on the condition variable), or commit to exiting by
@@ -198,10 +197,8 @@ maybe_t<work_request_t> thread_pool_t::dequeue_work_or_commit_to_exit() {
 }
 
 static void enqueue_thread_result(void_function_t req) {
-    s_result_queue.acquire()->push_back(std::move(req));
-    const char wakeup_byte = IO_SERVICE_RESULT_QUEUE;
-    int notify_fd = get_notify_pipes().write;
-    assert_with_errno(write_loop(notify_fd, &wakeup_byte, sizeof wakeup_byte) != -1);
+    s_main_thread_queue.acquire()->completions.push_back(std::move(req));
+    get_notify_signaller().post();
 }
 
 static void *this_thread() { return (void *)(intptr_t)pthread_self(); }
@@ -285,23 +282,9 @@ void iothread_perform_impl(void_function_t &&func, void_function_t &&completion,
     s_io_thread_pool.perform(std::move(func), std::move(completion), cant_wait);
 }
 
-int iothread_port() { return get_notify_pipes().read; }
+int iothread_port() { return get_notify_signaller().read_fd(); }
 
-void iothread_service_completion() {
-    ASSERT_IS_MAIN_THREAD();
-    // Drain the read buffer, and then service completions.
-    // The order is important.
-    int port = iothread_port();
-    char buff[256];
-    while (read(port, buff, sizeof buff) > 0) {
-        // pass
-    }
-
-    iothread_service_main_thread_requests();
-    iothread_service_result_queue();
-}
-
-static bool iothread_wait_for_pending_completions(long timeout_usec) {
+static bool iothread_wait_for_main_requests(long timeout_usec) {
     const long usec_per_sec = 1000000;
     struct timeval tv;
     tv.tv_sec = timeout_usec / usec_per_sec;
@@ -314,9 +297,9 @@ static bool iothread_wait_for_pending_completions(long timeout_usec) {
     return ret > 0;
 }
 
-void iothread_service_completion_with_timeout(long timeout_usec) {
-    if (iothread_wait_for_pending_completions(timeout_usec)) {
-        iothread_service_completion();
+void iothread_service_main_with_timeout(long timeout_usec) {
+    if (iothread_wait_for_main_requests(timeout_usec)) {
+        iothread_service_main();
     }
 }
 
@@ -344,9 +327,7 @@ int iothread_drain_all() {
 
     // Nasty polling via select().
     while (pool.req_data.acquire()->total_threads > 0) {
-        if (iothread_wait_for_pending_completions(1000)) {
-            iothread_service_completion();
-        }
+        iothread_service_main_with_timeout(1000);
     }
 
     // Clear the drain flag.
@@ -364,33 +345,29 @@ int iothread_drain_all() {
     return thread_count;
 }
 
-/// "Do on main thread" support.
-static void iothread_service_main_thread_requests() {
+// Service the main thread queue, by invoking any functions enqueued for the main thread.
+void iothread_service_main() {
     ASSERT_IS_MAIN_THREAD();
+    // Note the order here is important: we must consume events before handling requests, as posting
+    // uses the opposite order.
+    (void)get_notify_signaller().try_consume();
 
     // Move the queue to a local variable.
-    std::vector<main_thread_request_t *> request_queue;
-    s_main_thread_request_queue.acquire()->swap(request_queue);
+    // Note the s_main_thread_queue lock is not held after this.
+    main_thread_queue_t queue = s_main_thread_queue.acquire()->take();
 
-    // Perform each of the functions. Note we are NOT responsible for deleting these. They are
-    // stack allocated in their respective threads!
-    for (main_thread_request_t *req : request_queue) {
-        req->func();
-        req->done.set_value();
-    }
-}
-
-// Service the queue of results
-static void iothread_service_result_queue() {
-    // Move the queue to a local variable.
-    std::vector<void_function_t> result_queue;
-    s_result_queue.acquire()->swap(result_queue);
-
-    // Perform each completion in order
-    for (const auto &func : result_queue) {
+    // Perform each completion in order.
+    for (const void_function_t &func : queue.completions) {
         // ensure we don't invoke empty functions, that raises an exception
         if (func) func();
     }
+
+    // Perform each main thread request. Note we are NOT responsible for deleting these. They are
+    // stack allocated in their respective threads!
+    for (main_thread_request_t *req : queue.requests) {
+        req->func();
+        req->done.set_value();
+    }
 }
 
 void iothread_perform_on_main(void_function_t &&func) {
@@ -403,12 +380,10 @@ void iothread_perform_on_main(void_function_t &&func) {
     main_thread_request_t req(std::move(func));
 
     // Append it. Ensure we don't hold the lock after.
-    s_main_thread_request_queue.acquire()->push_back(&req);
+    s_main_thread_queue.acquire()->requests.push_back(&req);
 
-    // Tell the pipe and then wait until our future is set.
-    const char wakeup_byte = IO_SERVICE_MAIN_THREAD_REQUEST_QUEUE;
-    int notify_fd = get_notify_pipes().write;
-    assert_with_errno(write_loop(notify_fd, &wakeup_byte, sizeof wakeup_byte) != -1);
+    // Tell the signaller and then wait until our future is set.
+    get_notify_signaller().post();
     req.done.get_future().wait();
 }
 

src/iothread.h

@@ -14,11 +14,12 @@
 /// \return the fd on which to listen for completion callbacks.
 int iothread_port();
 
-/// Services iothread completion callbacks.
-void iothread_service_completion();
+/// Services iothread main thread completions and requests.
+/// This does not block.
+void iothread_service_main();
 
-/// Services completions, except does not wait more than \p timeout_usec.
-void iothread_service_completion_with_timeout(long timeout_usec);
+// Services any main thread requests. Does not wait more than \p timeout_usec.
+void iothread_service_main_with_timeout(long timeout_usec);
 
 /// Waits for all iothreads to terminate.
 /// \return the number of threads that were running.

src/reader.cpp

@@ -2480,9 +2480,9 @@ void reader_data_t::finish_highlighting_before_exec() {
     auto deadline = now + sc::milliseconds(kHighlightTimeoutForExecutionMs);
     while (now < deadline) {
         long timeout_usec = sc::duration_cast<sc::microseconds>(deadline - now).count();
-        iothread_service_completion_with_timeout(timeout_usec);
+        iothread_service_main_with_timeout(timeout_usec);
 
-        // Note iothread_service_completion_with_timeout will reentrantly modify us,
+        // Note iothread_service_main_with_timeout will reentrantly modify us,
         // by invoking a completion.
         if (in_flight_highlight_request.empty()) break;
         now = sc::steady_clock::now();