Issue #5138 has been updated by drbrain (Eric Hodel).


The goal is to avoid the creation hundreds (if not thousands) of Errno::EWOULDBLOCK, IO::WaitReadable and IO::WaitWritable exceptions (including their backtraces) that are immediately rescued in the course of a typical non-blocking socket read or write loop.

The usage should be as close to the same as possible to make it easy to modify code that currently uses exceptions.  This way users can quickly and easily switch to the new API without spending much time on it.
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Feature #5138: Add nonblocking IO that does not use exceptions for EOF and EWOULDBLOCK
https://bugs.ruby-lang.org/issues/5138#change-27606

Author: wycats (Yehuda Katz)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: 1.9.4


The current Ruby I/O classes have non-blocking methods (read_nonblock and write_nonblock). These methods will never block, and if they would block, they raise an exception instead (IO::WaitReadable or IO::WaitWritable). In addition, if the IO is at EOF, they raise an EOFError.

These exceptions are raised repeatedly in virtually every use of the non-blocking methods. This patch adds a pair of methods (try_read_nonblock and try_write_nonblock) that have the same semantics as the existing methods, but they return Symbols instead of raising exceptions for these routine cases:

* :read_would_block
* :write_would_block
* :eof

The patch contains updates for IO, StringIO, and OpenSSL. The updates are fully documented and tested.


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