=head1 NAME Async::Interrupt - allow C/XS libraries to interrupt perl asynchronously =head1 SYNOPSIS use Async::Interrupt; =head1 DESCRIPTION This module implements a single feature only of interest to advanced perl modules, namely asynchronous interruptions (think "unix signals", which are very similar). Sometimes, modules wish to run code asynchronously (in another thread), and then signal the perl interpreter on certain events. One common way is to write some data to a pipe and use an event handling toolkit to watch for I/O events. Another way is to send a signal. Those methods are slow, and in the case of a pipe, also not asynchronous - it won't interrupt a running perl interpreter. This module implements asynchronous notifications that enable you to signal running perl code form another thread, asynchronously, without issuing syscalls. It works by creating an C object for each such use. This object stores a perl and/or a C-level callback that is invoked when the C object gets signalled. It is executed at the next time the perl interpreter is running (i.e. it will interrupt a computation, but not an XS function or a syscall). You can signal the C object either by calling it's C<< ->signal >> method, or, more commonly, by calling a C function. The C<< ->signal_func >> returns the address of the C function that is to be called (plus an argument to be used during the call). The signalling function also takes an integer argument in the range SIG_ATOMIC_MIN to SIG_ATOMIC_MAX (guaranteed to allow at least 0..127). Since this kind of interruption is fast, but can only interrupt a I interpreter, there is optional support for also signalling a pipe - that means you can also wait for the pipe to become readable while =over 4 =cut package Async::Interrupt; no warnings; BEGIN { $VERSION = '0.02'; require XSLoader; XSLoader::load Async::Interrupt::, $VERSION; } our $DIED = sub { warn "$@" }; =item $async = new Async::Interrupt key => value... Creates a new Async::Interrupt object. You may only use async notifications on this object while it exists, so you need to keep a reference to it at all times while it is used. Optional constructor arguments include (normally you would specify at least one of C or C). =over 4 =item cb => $coderef->($value) Registers a perl callback to be invoked whenever the async interrupt is signalled. Note that, since this callback can be invoked at basically any time, it must not modify any well-known global variables such as C<$/> without restoring them again before returning. The exceptions are C<$!> and C<$@>, which are saved and restored by Async::Interrupt. If the callback should throw an exception, then it will be caught, and C<$Async::Interrupt::DIED> will be called with C<$@> containing the exception. The default will simply C about the message and continue. =item c_cb => [$c_func, $c_arg] Registers a C callback the be invoked whenever the async interrupt is signalled. The C callback must have the following prototype: void c_func (pTHX_ void *c_arg, int value); Both C<$c_func> and C<$c_arg> must be specified as integers/IVs, and C<$value> is the C passed to some earlier call to either C<$signal> or the C function. Note that, because the callback can be invoked at almost any time, you have to be careful at saving and restoring global variables that Perl might use (the excetpion is C, which is aved and restored by Async::Interrupt). The callback itself runs as part of the perl context, so you can call any perl functions and modify any perl data structures (in which case the requireemnts set out for C apply as well). =item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing] Specifies two file descriptors (or file handles) that should be signalled whenever the async interrupt is signalled. This means a single octet will be written to it, and before the callback is being invoked, it will be read again. Due to races, it is unlikely but possible that multiple octets are written. It is required that the file handles are both in nonblocking mode. (You can get a portable pipe and set non-blocking mode portably by using e.g. L from the L distro). The object will keep a reference to the file handles. This can be used to ensure that async notifications will interrupt event frameworks as well. =back =cut sub new { my ($class, %arg) = @_; bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1]), $class } =item ($signal_func, $signal_arg) = $async->signal_func Returns the address of a function to call asynchronously. The function has the following prototype and needs to be passed the specified C<$c_arg>, which is a C cast to C: void (*signal_func) (void *signal_arg, int value) An example call would look like: signal_func (signal_arg, 0); The function is safe to call from within signal and thread contexts, at any time. The specified C is passed to both C and Perl callback. C<$value> must be in the valid range for a C (0..127 is portable). If the function is called while the Async::Interrupt object is already signaled but before the callbacks are being executed, then the stored C is either the old or the new one. Due to the asynchronous nature of the code, the C can even be passed to two consecutive invocations of the callback. =item $async->signal ($value=0) This signals the given async object from Perl code. Semi-obviously, this will instantly trigger the callback invocation. C<$value> must be in the valid range for a C (0..127 is portable). =item $async->block Sometimes you need a "critical section" of code where =item $async->unblock =cut 1; =back =head1 EXAMPLE #TODO =head1 IMPLEMENTATION DETAILS AND LIMITATIONS This module works by "hijacking" SIGKILL, which is guarenteed to be always available in perl, but also cannot be caught, so is always available. Basically, this module fakes the receive of a SIGKILL signal and then catches it. This makes normal signal handling slower (probably unmeasurably), but has the advantage of not requiring a special runops nor slowing down normal perl execution a bit. It assumes that C and C are both exception-safe to modify (C is used by this module, and perl itself uses C, so we can assume that this is quite portbale, at least w.r.t. signals). =head1 AUTHOR Marc Lehmann http://home.schmorp.de/ =cut