More reliable macOS event loop (#1166)

* More reliable macOS event loop

* Reduce CPU usage of idling

* Add another implementation

* Add benchmark

Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>

1 files changed, 65 insertions, 0 deletions

diff --git a/src/io/io_darwin.cpp b/src/io/io_darwin.cpp
new file mode 100644
index 000000000..74a763812
--- /dev/null
+++ b/src/io/io_darwin.cpp
@@ -0,0 +1,65 @@
+
+#ifdef __APPLE__
+
+#include <sys/event.h>
+
+#include <mach/mach.h>
+// errno
+#include <errno.h>
+
+extern "C" mach_port_t io_darwin_create_machport(uint64_t wakeup, int32_t fd,
+                                                 void *wakeup_buffer_,
+                                                 size_t nbytes) {
+
+  mach_port_t port;
+  // Create a Mach port that will be used to wake up the pump
+  kern_return_t kr =
+      mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &port);
+  if (kr != KERN_SUCCESS) {
+    return 0;
+  }
+
+  // Configure the event to directly receive the Mach message as part of the
+  // kevent64() call.
+  kevent64_s event{};
+  event.ident = port;
+  event.filter = EVFILT_MACHPORT;
+  event.flags = EV_ADD | EV_ENABLE;
+  event.fflags = MACH_RCV_MSG | MACH_RCV_OVERWRITE;
+  event.ext[0] = reinterpret_cast<uint64_t>(wakeup_buffer_);
+  event.ext[1] = nbytes;
+
+  while (true) {
+    int rv = kevent64(fd, &event, 1, NULL, 0, 0, NULL);
+    if (rv == -1) {
+      if (errno == EINTR) {
+        continue;
+      }
+
+      return 0;
+    }
+
+    return port;
+  }
+}
+
+extern "C" bool io_darwin_schedule_wakeup(mach_port_t waker) {
+  mach_msg_empty_send_t message{};
+  message.header.msgh_size = sizeof(message);
+  message.header.msgh_bits =
+      MACH_MSGH_BITS_REMOTE(MACH_MSG_TYPE_MAKE_SEND_ONCE);
+  message.header.msgh_remote_port = waker;
+  kern_return_t kr = mach_msg_send(&message.header);
+  if (kr != KERN_SUCCESS) {
+    // If io_darwin_schedule_wakeup() is being called by other threads faster
+    // than the pump can dispatch work, the kernel message queue for the wakeup
+    // port can fill The kernel does return a SEND_ONCE right in the case of
+    // failure, which must be destroyed to avoid leaking.
+    mach_msg_destroy(&message.header);
+    return false;
+  }
+
+  return true;
+}
+
+#endif
\ No newline at end of file