Thread(3p) Perl Programmers Reference Guide Thread(3p) #
Thread(3p) Perl Programmers Reference Guide Thread(3p)
NNAAMMEE #
Thread - Manipulate threads in Perl (for old code only)
DDEEPPRREECCAATTEEDD #
The "Thread" module served as the frontend to the old-style thread model,
called _5_0_0_5_t_h_r_e_a_d_s, that was introduced in release 5.005. That model was
deprecated, and has been removed in version 5.10.
For old code and interim backwards compatibility, the "Thread" module has
been reworked to function as a frontend for the new interpreter threads
(_i_t_h_r_e_a_d_s) model. However, some previous functionality is not available.
Further, the data sharing models between the two thread models are
completely different, and anything to do with data sharing has to be
thought differently. With _i_t_h_r_e_a_d_s, you must explicitly "share()"
variables between the threads.
You are strongly encouraged to migrate any existing threaded code to the
new model (i.e., use the "threads" and "threads::shared" modules) as soon
as possible.
HHIISSTTOORRYY #
In Perl 5.005, the thread model was that all data is implicitly shared,
and shared access to data has to be explicitly synchronized. This model
is called _5_0_0_5_t_h_r_e_a_d_s.
In Perl 5.6, a new model was introduced in which all is was thread local
and shared access to data has to be explicitly declared. This model is
called _i_t_h_r_e_a_d_s, for "interpreter threads".
In Perl 5.6, the _i_t_h_r_e_a_d_s model was not available as a public API; only
as an internal API that was available for extension writers, and to
implement ffoorrkk(()) emulation on Win32 platforms.
In Perl 5.8, the _i_t_h_r_e_a_d_s model became available through the "threads"
module, and the _5_0_0_5_t_h_r_e_a_d_s model was deprecated.
In Perl 5.10, the _5_0_0_5_t_h_r_e_a_d_s model was removed from the Perl
interpreter.
SSYYNNOOPPSSIISS #
use Thread qw(:DEFAULT async yield);
my $t = Thread->new(\&start_sub, @start_args);
$result = $t->join;
$t->detach;
if ($t->done) {
$t->join;
}
if($t->equal($another_thread)) {
# ...
}
yield();
my $tid = Thread->self->tid;
lock($scalar);
lock(@array);
lock(%hash);
my @list = Thread->list;
DDEESSCCRRIIPPTTIIOONN #
The "Thread" module provides multithreading support for Perl.
FFUUNNCCTTIIOONNSS #
$thread = Thread->new(\&start_sub)
$thread = Thread->new(\&start_sub, LIST)
"new" starts a new thread of execution in the referenced
subroutine. The optional list is passed as parameters to the
subroutine. Execution continues in both the subroutine and the
code after the "new" call.
"Thread->new" returns a thread object representing the newly
created thread.
lock VARIABLE
"lock" places a lock on a variable until the lock goes out of
scope.
If the variable is locked by another thread, the "lock" call will
block until it's available. "lock" is recursive, so multiple
calls to "lock" are safe--the variable will remain locked until
the outermost lock on the variable goes out of scope.
Locks on variables only affect "lock" calls--they do _n_o_t affect
normal access to a variable. (Locks on subs are different, and
covered in a bit.) If you really, _r_e_a_l_l_y want locks to block
access, then go ahead and tie them to something and manage this
yourself. This is done on purpose. While managing access to
variables is a good thing, Perl doesn't force you out of its
living room...
If a container object, such as a hash or array, is locked, all
the elements of that container are not locked. For example, if a
thread does a "lock @a", any other thread doing a "lock($a[12])"
won't block.
Finally, "lock" will traverse up references exactly _o_n_e level.
"lock(\$a)" is equivalent to "lock($a)", while "lock(\\$a)" is
not.
async BLOCK;
"async" creates a thread to execute the block immediately
following it. This block is treated as an anonymous sub, and so
must have a semi-colon after the closing brace. Like
"Thread->new", "async" returns a thread object.
Thread->self
The "Thread->self" function returns a thread object that
represents the thread making the "Thread->self" call.
Thread->list
Returns a list of all non-joined, non-detached Thread objects.
cond_wait VARIABLE
The "cond_wait" function takes a lloocckkeedd variable as a parameter,
unlocks the variable, and blocks until another thread does a
"cond_signal" or "cond_broadcast" for that same locked variable.
The variable that "cond_wait" blocked on is relocked after the
"cond_wait" is satisfied. If there are multiple threads
"cond_wait"ing on the same variable, all but one will reblock
waiting to re-acquire the lock on the variable. (So if you're
only using "cond_wait" for synchronization, give up the lock as
soon as possible.)
cond_signal VARIABLE
The "cond_signal" function takes a locked variable as a parameter
and unblocks one thread that's "cond_wait"ing on that variable.
If more than one thread is blocked in a "cond_wait" on that
variable, only one (and which one is indeterminate) will be
unblocked.
If there are no threads blocked in a "cond_wait" on the variable,
the signal is discarded.
cond_broadcast VARIABLE
The "cond_broadcast" function works similarly to "cond_signal".
"cond_broadcast", though, will unblock aallll the threads that are
blocked in a "cond_wait" on the locked variable, rather than only
one.
yield The "yield" function allows another thread to take control of the
CPU. The exact results are implementation-dependent.
MMEETTHHOODDSS #
join "join" waits for a thread to end and returns any values the
thread exited with. "join" will block until the thread has
ended, though it won't block if the thread has already
terminated.
If the thread being "join"ed "die"d, the error it died with will
be returned at this time. If you don't want the thread performing
the "join" to die as well, you should either wrap the "join" in
an "eval" or use the "eval" thread method instead of "join".
detach "detach" tells a thread that it is never going to be joined i.e.
that all traces of its existence can be removed once it stops
running. Errors in detached threads will not be visible anywhere
- if you want to catch them, you should use $SIG{__DIE__} or
something like that.
equal "equal" tests whether two thread objects represent the same
thread and returns true if they do.
tid The "tid" method returns the tid of a thread. The tid is a
monotonically increasing integer assigned when a thread is
created. The main thread of a program will have a tid of zero,
while subsequent threads will have tids assigned starting with
one.
done The "done" method returns true if the thread you're checking has
finished, and false otherwise.
DDEEFFUUNNCCTT #
The following were implemented with _5_0_0_5_t_h_r_e_a_d_s, but are no longer
available with _i_t_h_r_e_a_d_s.
lock(\&sub)
With 5005threads, you could also "lock" a sub such that any calls
to that sub from another thread would block until the lock was
released.
Also, subroutines could be declared with the ":locked" attribute
which would serialize access to the subroutine, but allowed
different threads non-simultaneous access.
eval The "eval" method wrapped an "eval" around a "join", and so
waited for a thread to exit, passing along any values the thread
might have returned and placing any errors into $@.
flags The "flags" method returned the flags for the thread - an integer
value corresponding to the internal flags for the thread.
SSEEEE AALLSSOO #
threads, threads::shared, Thread::Queue, Thread::Semaphore
perl v5.36.3 2021-03-02 Thread(3p)