Feature #10718
Updated by akr (Akira Tanaka) almost 10 years ago
I'd like to change IO#close.
It should not raise IOError on closed IO objects.
We sometimes invoke IO#close only when the IO object is not closed as:
```
f.close if !f.closed?
```
If this issue is accepted, we can write it simply as follows.
```
f.close
```
Simple grep finds many examples.
Following examples are just a little excerpt.
```
lib/webrick/server.rb: sock.close unless sock.closed?
lib/pstore.rb: file.close if !file.closed?
lib/mkmf.rb: @log.close if @log and not @log.closed?
lib/cgi/session.rb: f.close if f and !f.closed?
lib/open-uri.rb: io.close if !io.closed?
lib/net/pop.rb: s.close if s and not s.closed?
lib/net/http.rb: @socket.close if @socket and not @socket.closed?
lib/net/smtp.rb: s.close if s and not s.closed?
lib/shell/process-controller.rb: io.close unless io.closed?
test/ruby/test_io.rb: w.close unless !w || w.closed?
...
```
I think there is no problem with the behavior which IO#close doesn't raise an exception on closed IO object.
Because the closed state fulfils the postcondition of the method.
The change means relaxing the precondition which should be harmless.
Moreover raising IOError can smash other exceptions if it is called in ensure clause.
It makes debugging difficult and the proposed behavior ease it.
It also useful to close IO object asynchronously.
Asynchronous close can be used for graceful shutdown.
This issue can eliminate "rescue IOError".
See lib/webrick/server.rb and lib/drb/drb.rb for example.
Note that "double close" is a bad idea in C.
But it is not applicable to Ruby.
A FILE structure is freed on fclose().
But Ruby's IO object is not freed until GC.
So method invocation on closed object doesn't cause invalid memory access.
A file descriptor (FD) can be reused any time because a signal handler or another thread may allocate a FD.
But Ruby's IO object is not reused after close.
So it is impossible to close an IO object unintentionally.