[ViewVC] Diff of: cvs/cvsroot/Coro/Coro.pm

Comparing cvsroot/Coro/Coro.pm (file contents):
Revision 1.293 by root, Sat Apr 30 05:20:03 2011 UTC vs.
Revision 1.295 by root, Tue May 10 19:55:48 2011 UTC

    async {
       Coro::terminate "return value 1", "return value 2";
    };
-And yet another way is to C<< ->cancel >> the coro thread from another
+And yet another way is to C<< ->cancel >> (or C<< ->safe_cancel >>) the
-thread:
+coro thread from another thread:
    my $coro = async {
       exit 1;
    };
-   $coro->cancel; # an also accept values for ->join to retrieve
+   $coro->cancel; # also accepts values for ->join to retrieve
 Cancellation I<can> be dangerous - it's a bit like calling C<exit> without
 actually exiting, and might leave C libraries and XS modules in a weird
 state. Unlike other thread implementations, however, Coro is exceptionally
 safe with regards to cancellation, as perl will always be in a consistent
-state.
+state, and for those cases where you want to do truly marvellous things
+with your coro while it is being cancelled - that is, make sure all
+cleanup code is executed from the thread being cancelled - there is even a
+C<< ->safe_cancel >> method.
 So, cancelling a thread that runs in an XS event loop might not be the
 best idea, but any other combination that deals with perl only (cancelling
 when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
 safe.
 Returns true iff this Coro object has been suspended. Suspended Coros will
 not ever be scheduled.
 =item $coro->cancel (arg...)
-Terminates the given Coro object and makes it return the given arguments as
+Terminates the given Coro thread and makes it return the given arguments as
 status (default: an empty list). Never returns if the Coro is the
 current Coro.
-The arguments are not copied, but instead will be referenced directly
+This is a rather brutal way to free a coro, with some limitations - if
-(e.g. if you pass C<$var> and after the call change that variable, then
+the thread is inside a C callback that doesn't expect to be canceled,
-you might change the return values passed to e.g. C<join>, so don't do
+bad things can happen, or if the cancelled thread insists on running
-that).
+complicated cleanup handlers that rely on it'S thread context, things will
+not work.
+Any cleanup code being run (e.g. from C<guard> blocks) will be run without
+a thread context, and is not allowed to switch to other threads. On the
+plus side, C<< ->cancel >> will always clean up the thread, no matter
+what.  If your cleanup code is complex or you want to avoid cancelling a
+C-thread that doesn't know how to clean up itself, it can be better to C<<
+->throw >> an exception, or use C<< ->safe_cancel >>.
+The arguments to C<< ->cancel >> are not copied, but instead will
+be referenced directly (e.g. if you pass C<$var> and after the call
+change that variable, then you might change the return values passed to
+e.g. C<join>, so don't do that).
 The resources of the Coro are usually freed (or destructed) before this
 call returns, but this can be delayed for an indefinite amount of time, as
 in some cases the manager thread has to run first to actually destruct the
 Coro object.
+=item $coro->safe_cancel ($arg...)
+Works mostly like C<< ->cancel >>, but is inherently "safer", and
+consequently, can fail with an exception in cases the thread is not in a
+cancellable state.
+This method works a bit like throwing an exception that cannot be caught
+- specifically, it will clean up the thread from within itself, so
+all cleanup handlers (e.g. C<guard> blocks) are run with full thread
+context and can block if they wish. The downside is that there is no
+guarantee that the thread can be cancelled when you call this method, and
+therefore, it might fail. It is also considerably slower than C<cancel> or
+C<terminate>.
+A thread is in a safe-cancellable state if it either hasn't been run yet,
+or it has no C context attached and is inside an SLF function.
+The latter two basically mean that the thread isn't currently inside a
+perl callback called from some C function (usually via some XS modules)
+and isn't currently executing inside some C function itself (via Coro's XS
+API).
+This call returns true when it could cancel the thread, or croaks with an
+error otherwise (i.e. it either returns true or doesn't return at all).
+Why the weird interface? Well, there are two common models on how and
+when to cancel things. In the first, you have the expectation that your
+coro thread can be cancelled when you want to cancel it - if the thread
+isn't cancellable, this would be a bug somewhere, so C<< ->safe_cancel >>
+croaks to notify of the bug.
+In the second model you sometimes want to ask nicely to cancel a thread,
+but if it's not a good time, well, then don't cancel. This can be done
+relatively easy like this:
+   if (! eval { $coro->safe_cancel }) {
+      warn "unable to cancel thread: $@";
+   }
+However, what you never should do is first try to cancel "safely" and
+if that fails, cancel the "hard" way with C<< ->cancel >>. That makes
+no sense: either you rely on being able to execute cleanup code in your
+thread context, or you don't. If you do, then C<< ->safe_cancel >> is the
+only way, and if you don't, then C<< ->cancel >> is always faster and more
+direct.
 =item $coro->schedule_to
 Puts the current coro to sleep (like C<Coro::schedule>), but instead
 of continuing with the next coro from the ready queue, always switch to
 the given coro object (regardless of priority etc.). The readyness
 inside the coro at the next convenient point in time. Otherwise
 clears the exception object.
 Coro will check for the exception each time a schedule-like-function
 returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
->>, C<< Coro::Handle->readable >> and so on. Most of these functions
+>>, C<< Coro::Handle->readable >> and so on. Most of those functions (all
-detect this case and return early in case an exception is pending.
+that are part of Coro itself) detect this case and return early in case an
+exception is pending.
 The exception object will be thrown "as is" with the specified scalar in
 C<$@>, i.e. if it is a string, no line number or newline will be appended
 (unlike with C<die>).
-This can be used as a softer means than C<cancel> to ask a coro to
+This can be used as a softer means than either C<cancel> or C<safe_cancel
-end itself, although there is no guarantee that the exception will lead to
+>to ask a coro to end itself, although there is no guarantee that the
-termination, and if the exception isn't caught it might well end the whole
+exception will lead to termination, and if the exception isn't caught it
-program.
+might well end the whole program.
 You might also think of C<throw> as being the moral equivalent of
 C<kill>ing a coro with a signal (in this case, a scalar).
 =item $coro->join
       };
       &schedule while $current;
    }
-   wantarray ? @{$self->{_status}} : $self->{_status}[0];
+   wantarray ? @{$self->{_status}} : $self->{_status}[0]
 }
 =item $coro->on_destroy (\&cb)
 Registers a callback that is called when this coro thread gets destroyed,

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Comparing cvsroot/Coro/Coro.pm (file contents): Revision 1.293 by root, Sat Apr 30 05:20:03 2011 UTC vs. Revision 1.295 by root, Tue May 10 19:55:48 2011 UTC

Diff Legend

Comparing cvsroot/Coro/Coro.pm (file contents):
Revision 1.293 by root, Sat Apr 30 05:20:03 2011 UTC vs.
Revision 1.295 by root, Tue May 10 19:55:48 2011 UTC