Document the effect of thread creation context.

[p5sagit/p5-mst-13.2.git] / ext / threads / threads.pm

diff --git a/ext/threads/threads.pm b/ext/threads/threads.pm
index bb86939..6e2f0ef 100755 (executable)
--- a/ext/threads/threads.pm
+++ b/ext/threads/threads.pm
@@ -151,11 +151,18 @@ object. The new() method is an alias for create().
 This will wait for the corresponding thread to join. When the thread
 finishes, join() will return the return values of the entry point
 function. If the thread has been detached, an error will be thrown.
+
+The context (scalar or list) of the thread creation is also the
+context for join().  This means that if you intend to return an array
+from a thread, you must use C<my ($thread) = threads->new(...)>, and
+that if you intend to return a scalar, you must use C<my $thread = ...>.
+
 If the program exits without all other threads having been either
 joined or detached, then a warning will be issued. (A program exits
 either because one of its threads explicitly calls exit(), or in the
 case of the main thread, reaches the end of the main program file.)
 
+
 =item $thread->detach
 
 Will make the thread unjoinable, and cause any eventual return value
@@ -217,7 +224,7 @@ exit from the main thread.
 
 =back
 
-=head1 BUGS / TODO
+=head1 TODO
 
 The current implementation of threads has been an attempt to get
 a correct threading system working that could be built on, 
@@ -228,6 +235,8 @@ also the cost of returning values can be large. These are areas
 were there most likely will be work done to optimize what data
 that needs to be cloned.
 
+=head1 BUGS
+
 =over
 
 =item Parent-Child threads.
@@ -235,8 +244,8 @@ that needs to be cloned.
 On some platforms it might not be possible to destroy "parent"
 threads while there are still existing child "threads".
 
-This will be possibly be fixed in later versions of perl.
-
+This will possibly be fixed in later versions of perl.
+  
 =item tid is I32
 
 The thread id is a 32 bit integer, it can potentially overflow.
@@ -248,8 +257,19 @@ When you return an object the entire stash that the object is blessed
 as well.  This will lead to a large memory usage.  The ideal situation
 would be to detect the original stash if it existed.
 
+=item Creating threads inside BEGIN blocks
+
+Creating threads inside BEGIN blocks (or during the compilation phase
+in general) does not work.  (In Windows, trying to use fork() inside
+BEGIN blocks is an equally losing proposition, since it has been
+implemented in very much the same way as threads.)
+
 =item PERL_OLD_SIGNALS are not threadsafe, will not be.
 
+If your Perl has been built with PERL_OLD_SIGNALS (one has
+to explicitly add that symbol to ccflags, see C<perl -V>),
+signal handling is not threadsafe.
+
 =back
 
 =head1 AUTHOR and COPYRIGHT