Fix: make Crystal::EventLoop#remove(io) a class method

The method is called from IO::FileDescriptor and Socket finalizers,
which means they can be run from any thread during GC collections, yet
calling an instance method means accessing the current event loop, which
may have not been instantiated yet for the thread.

Fix: replace typeof for backend_class accessor

The API won't change if we start having two potential event loop
implementations in a single binary (e.g. io_uring with a fallback to
epoll).

src/crystal/event_loop.cr

@@ -1,26 +1,30 @@
 abstract class Crystal::EventLoop
-  # Creates an event loop instance
-  def self.create : self
+  def self.backend_class
     {% if flag?(:wasi) %}
-      Crystal::EventLoop::Wasi.new
+      Crystal::EventLoop::Wasi
     {% elsif flag?(:unix) %}
       # TODO: enable more targets by default (need manual tests or fixes)
       {% if flag?("evloop=libevent") %}
-        Crystal::EventLoop::LibEvent.new
+        Crystal::EventLoop::LibEvent
       {% elsif flag?("evloop=epoll") || flag?(:android) || flag?(:linux) %}
-        Crystal::EventLoop::Epoll.new
+        Crystal::EventLoop::Epoll
       {% elsif flag?("evloop=kqueue") || flag?(:darwin) || flag?(:freebsd) %}
-        Crystal::EventLoop::Kqueue.new
+        Crystal::EventLoop::Kqueue
       {% else %}
-        Crystal::EventLoop::LibEvent.new
+        Crystal::EventLoop::LibEvent
       {% end %}
     {% elsif flag?(:win32) %}
-      Crystal::EventLoop::IOCP.new
+      Crystal::EventLoop::IOCP
     {% else %}
       {% raise "Event loop not supported" %}
     {% end %}
   end
 
+  # Creates an event loop instance
+  def self.create : self
+    backend_class.new
+  end
+
   @[AlwaysInline]
   def self.current : self
     {% if flag?(:execution_context) %}

src/crystal/event_loop/file_descriptor.cr

@@ -19,13 +19,20 @@ abstract class Crystal::EventLoop
 
     # Closes the file descriptor resource.
     abstract def close(file_descriptor : Crystal::System::FileDescriptor) : Nil
+  end
 
-    # Removes the file descriptor from the event loop. Can be used to free up
-    # memory resources associated with the file descriptor, as well as removing
-    # the file descriptor from kernel data structures.
-    #
-    # Called by `::IO::FileDescriptor#finalize` before closing the file
-    # descriptor. Errors shall be silently ignored.
-    abstract def remove(file_descriptor : Crystal::System::FileDescriptor) : Nil
+  # Removes the file descriptor from the event loop. Can be used to free up
+  # memory resources associated with the file descriptor, as well as removing
+  # the file descriptor from kernel data structures.
+  #
+  # Called by `::IO::FileDescriptor#finalize` before closing the file
+  # descriptor. Errors shall be silently ignored.
+  def self.remove(file_descriptor : Crystal::System::FileDescriptor) : Nil
+    backend_class.remove_impl(file_descriptor)
+  end
+
+  # Actual implementation for `.remove`. Must be implemented on a subclass of
+  # `Crystal::EventLoop` when needed.
+  protected def self.remove_impl(file_descriptor : Crystal::System::FileDescriptor) : Nil
   end
 end

src/crystal/event_loop/iocp.cr

@@ -209,9 +209,6 @@ class Crystal::EventLoop::IOCP < Crystal::EventLoop
     LibC.CancelIoEx(file_descriptor.windows_handle, nil) unless file_descriptor.system_blocking?
   end
 
-  def remove(file_descriptor : Crystal::System::FileDescriptor) : Nil
-  end
-
   private def wsa_buffer(bytes)
     wsabuf = LibC::WSABUF.new
     wsabuf.len = bytes.size
@@ -322,7 +319,4 @@ class Crystal::EventLoop::IOCP < Crystal::EventLoop
 
   def close(socket : ::Socket) : Nil
   end
-
-  def remove(socket : ::Socket) : Nil
-  end
 end

src/crystal/event_loop/libevent.cr

@@ -128,9 +128,6 @@ class Crystal::EventLoop::LibEvent < Crystal::EventLoop
     file_descriptor.evented_close
   end
 
-  def remove(file_descriptor : Crystal::System::FileDescriptor) : Nil
-  end
-
   def read(socket : ::Socket, slice : Bytes) : Int32
     evented_read(socket, "Error reading socket") do
       LibC.recv(socket.fd, slice, slice.size, 0).to_i32
@@ -224,9 +221,6 @@ class Crystal::EventLoop::LibEvent < Crystal::EventLoop
     socket.evented_close
   end
 
-  def remove(socket : ::Socket) : Nil
-  end
-
   def evented_read(target, errno_msg : String, &) : Int32
     loop do
       bytes_read = yield

src/crystal/event_loop/polling.cr

@@ -175,7 +175,7 @@ abstract class Crystal::EventLoop::Polling < Crystal::EventLoop
     evented_close(file_descriptor)
   end
 
-  def remove(file_descriptor : System::FileDescriptor) : Nil
+  protected def self.remove_impl(file_descriptor : System::FileDescriptor) : Nil
     internal_remove(file_descriptor)
   end
 
@@ -278,7 +278,7 @@ abstract class Crystal::EventLoop::Polling < Crystal::EventLoop
     evented_close(socket)
   end
 
-  def remove(socket : ::Socket) : Nil
+  protected def self.remove_impl(socket : ::Socket) : Nil
     internal_remove(socket)
   end
 
@@ -336,7 +336,7 @@ abstract class Crystal::EventLoop::Polling < Crystal::EventLoop
     end
   end
 
-  private def internal_remove(io)
+  private def self.internal_remove(io)
     return unless (index = io.__evloop_data).valid?
 
     Polling.arena.free(index) do |pd|

src/crystal/event_loop/socket.cr

@@ -62,13 +62,20 @@ abstract class Crystal::EventLoop
 
     # Closes the socket.
     abstract def close(socket : ::Socket) : Nil
+  end
 
-    # Removes the socket from the event loop. Can be used to free up memory
-    # resources associated with the socket, as well as removing the socket from
-    # kernel data structures.
-    #
-    # Called by `::Socket#finalize` before closing the socket. Errors shall be
-    # silently ignored.
-    abstract def remove(socket : ::Socket) : Nil
+  # Removes the socket from the event loop. Can be used to free up memory
+  # resources associated with the socket, as well as removing the socket from
+  # kernel data structures.
+  #
+  # Called by `::Socket#finalize` before closing the socket. Errors shall be
+  # silently ignored.
+  def self.remove(socket : ::Socket) : Nil
+    backend_class.remove_impl(socket)
+  end
+
+  # Actual implementation for `.remove`. Must be implemented on a subclass of
+  # `Crystal::EventLoop` when needed.
+  protected def self.remove_impl(socket : ::Socket) : Nil
   end
 end

src/crystal/event_loop/wasi.cr

@@ -53,9 +53,6 @@ class Crystal::EventLoop::Wasi < Crystal::EventLoop
     file_descriptor.evented_close
   end
 
-  def remove(file_descriptor : Crystal::System::FileDescriptor) : Nil
-  end
-
   def read(socket : ::Socket, slice : Bytes) : Int32
     evented_read(socket, "Error reading socket") do
       LibC.recv(socket.fd, slice, slice.size, 0).to_i32
@@ -88,9 +85,6 @@ class Crystal::EventLoop::Wasi < Crystal::EventLoop
     socket.evented_close
   end
 
-  def remove(socket : ::Socket) : Nil
-  end
-
   def evented_read(target, errno_msg : String, &) : Int32
     loop do
       bytes_read = yield

src/crystal/system/unix/process.cr

@@ -352,7 +352,7 @@ struct Crystal::System::Process
 
   private def self.reopen_io(src_io : IO::FileDescriptor, dst_io : IO::FileDescriptor)
     if src_io.closed?
-      Crystal::EventLoop.current.remove(dst_io)
+      Crystal::EventLoop.remove(dst_io)
       dst_io.file_descriptor_close
     else
       src_io = to_real_fd(src_io)

src/crystal/system/unix/signal.cr

@@ -112,7 +112,7 @@ module Crystal::System::Signal
   # descriptors of the parent process and send it received signals.
   def self.after_fork
     @@pipe.each do |pipe_io|
-      Crystal::EventLoop.current.remove(pipe_io)
+      Crystal::EventLoop.remove(pipe_io)
       pipe_io.file_descriptor_close { }
     end
   ensure

src/io/file_descriptor.cr

@@ -255,7 +255,7 @@ class IO::FileDescriptor < IO
   def finalize
     return if closed? || !close_on_finalize?
 
-    event_loop?.try(&.remove(self))
+    Crystal::EventLoop.remove(self)
     file_descriptor_close { } # ignore error
   end
 

src/socket.cr

@@ -430,7 +430,7 @@ class Socket < IO
   def finalize
     return if closed?
 
-    event_loop?.try(&.remove(self))
+    Crystal::EventLoop.remove(self)
     socket_close { } # ignore error
   end