IO: Detect closed IO when resuming readable/writable event

src/crystal/system/file.cr

@@ -40,6 +40,13 @@ module Crystal::System::File
 
     oflag = m | o
   end
+
+  # Closes the internal file descriptor without notifying libevent.
+  # This is directly used after the fork of a process to close the
+  # parent's Crystal::Signal.@@pipe reference before re initializing
+  # the event loop. In the case of a fork that will exec there is even
+  # no need to initialize the event loop at all.
+  # def file_description_close
 end
 
 {% if flag?(:unix) %}

src/crystal/system/unix/file_descriptor.cr

@@ -115,6 +115,10 @@ module Crystal::System::FileDescriptor
     # always lead to undefined results. This is not specific to libevent.
     evented_close
 
+    file_description_close
+  end
+
+  def file_description_close
     if LibC.close(@fd) != 0
       case Errno.value
       when Errno::EINTR, Errno::EINPROGRESS

src/crystal/system/win32/file_descriptor.cr

@@ -114,6 +114,10 @@ module Crystal::System::FileDescriptor
   end
 
   private def system_close
+    file_description_close
+  end
+
+  def file_description_close
     err = nil
     if LibC._close(@fd) != 0
       case Errno.value

src/signal.cr

@@ -220,7 +220,7 @@ module Crystal::Signal
   # Replaces the signal pipe so the child process won't share the file
   # descriptors of the parent process and send it received signals.
   def self.after_fork
-    @@pipe.each(&.close)
+    @@pipe.each(&.file_description_close)
   ensure
     @@pipe = IO.pipe(read_blocking: false, write_blocking: true)
   end
@@ -243,7 +243,7 @@ module Crystal::Signal
     end
   ensure
     {% unless flag?(:preview_mt) %}
-      @@pipe.each(&.close)
+      @@pipe.each(&.file_description_close)
     {% end %}
   end