Add extra debug information when failing to deliver an interrupt message.

runtime/bin/eventhandler_macos.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <errno.h>
 #include <poll.h>
 #include <pthread.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/time.h>
@@ skipping 77 matching lines @@
 void EventHandlerImplementation::WakeupHandler(intptr_t id,
                                                Dart_Port dart_port,
                                                int64_t data) {
   InterruptMessage msg;
   msg.id = id;
   msg.dart_port = dart_port;
   msg.data = data;
   intptr_t result =
       FDUtils::WriteToBlocking(interrupt_fds_[1], &msg, kInterruptMessageSize);
   if (result != kInterruptMessageSize) {
-    FATAL("Interrupt message failure");
+    if (result == -1) {
+      perror("Interrupt message failure:");
+    }
+    FATAL1("Interrupt message failure. Wrote %d bytes.", result);
   }
 }
 
 
 struct pollfd* EventHandlerImplementation::GetPollFds(intptr_t* pollfds_size) {
   struct pollfd* pollfds;
 
   // Calculate the number of file descriptors to poll on.
   intptr_t numPollfds = 1;
   for (HashMap::Entry* entry = socket_map_.Start();
@@ skipping 271 matching lines @@
 void* EventHandlerImplementation::GetHashmapKeyFromFd(intptr_t fd) {
   // The hashmap does not support keys with value 0.
   return reinterpret_cast<void*>(fd + 1);
 }
 
 
 uint32_t EventHandlerImplementation::GetHashmapHashFromFd(intptr_t fd) {
   // The hashmap does not support keys with value 0.
   return dart::Utils::WordHash(fd + 1);
 }