Perl - Term::TermKey - version 0.09

Last week saw a new version of Term::TermKey (0.09), and also the underlying libtermkey (0.9). This contains a fairly small new feature, giving control of the way that EINTR is handled.

Version 0.8 added graceful handling of EINTR to restart IO operations rather than fail with an error. This had unfortunate knock-on effects for the Perl-level wrapping of it, because of the deferred nature of Perl's safe signals. On a signal (such as the not-so-unlikely SIGWINCH) a flag would be set, but the termkey_waitkey(3) operation would be restarted, not returning back to Perl's control until a keypress event was actually received. This upset programs that wish to respond to SIGWINCH and redraw the terminal to the new size.

Version 0.9 of libtermkey now therefore has a new flag, TERMKEY_FLAG_EINTR whose presence makes the blocking IO operations (termkey_waitkey(3) and termkey_advisereadable(3)) to return a new result code, TERMKEY_RES_ERROR after which the caller can inspect the value of errno, to observe an EINTR.

Again because of Perl's safe signal handling, the Perl wrapping of libtermkey has to always enable this flag, so it can invoke the $SIG{WINCH} signal handler, for example. The Term::TermKey module therefore now always sets TERMKEY_FLAG_EINTR on the underlying TermKey instance, and emulates the presence or absence of this flag at the Perl level, by optionally restarting its IO operation, or itself returning TERMKEY_RES_ERROR.

An unfortunate bug here in the emulation and hiding of this flag from the Perl level means that Term::TermKey 0.09 fails to correctly read the TermKey flags back out of the underlying object. In particular it fails to be able to check on the presence of TERMKEY_FLAG_UTF8 that libtermkey itself may have enabled, after detecting a UTF-8 locale. This causes Tickit's unit tests to break with the familiar "Wide character in syswrite at ..." error.

This bug has now been fixed in the source code repository, and will be present in the next version, 0.10. Tickit 0.10 also has an independent fix for the same bug, by using Perl's ${^UTF8LOCALE} instead of reading the TermKey flags back out again.

Also upcoming in libtermkey 0.10, will be some Solaris portability fixes, and a new canonicalisation flag, which turns a TERMKEY_SYM_DEL key into TERMKEY_SYM_BACKSPACE, for those terminals that send DEL on Backspace.


IO::Async and AnyEvent

I've recently been working on a new IO::Async loop implementation, IO::Async::Loop::AnyEvent. Like the Glib and POE loops, this one uses another event system as its underlying implementation; AnyEvent.

What makes this one a little different and noteworthy, is that AnyEvent claims not to be an event system as such, but rather a compatibility layer on top of event systems. I have so far resisted writing this particular loop implementation on the grounds that, since AnyEvent just applies a cross-compatibility layer on top of some other existing event system anyway, IO::Async might as well use that underlying event system directly. In practice however this doesn't quite seem to work out all the time; existing code exists and is already written. Sometimes that existing code already works using AnyEvent directly, making it harder to drop a small section of IO::Async-based code inside it.

In that situation, an individual module/function/etc.. can construct itself an IO::Async::Loop::AnyEvent, to allow that component to use IO::Async-based functionallity, while still interacting correctly with the rest of the AnyEvent-based program.

It is not primarily intended that this module be used as the basis of an entire program; mostly because a neater solution for mixed IO::Async+AnyEvent exists in the form of AnyEvent::Impl::IOAsync.

There are still some minor issues to deal with currently; most notably that because each of IO::Async and AnyEvent could use the other as an event source, there are some circularity problems when AnyEvent picks AnyEvent::Impl::IOAsync to use, when IO::Async::Loop::AnyEvent loads it.
Deep recursion on subroutine "AnyEvent::Impl::IOAsync::io" at /home/leo/src/perl/IO-Async-Loop-AnyEvent/blib/lib/IO/Async/Loop/AnyEvent.pm line 103.
Hmmmmm.... A little work there still needed :)