summaryrefslogtreecommitdiff
path: root/Master/tlpkg/tlperl/lib/Thread/Queue.pm
blob: 8588ed58458d6c0243d8dc5326177e637aa92a5d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
package Thread::Queue;

use strict;
use warnings;

our $VERSION = '2.12';
$VERSION = eval $VERSION;

use threads::shared 1.21;
use Scalar::Util 1.10 qw(looks_like_number blessed reftype refaddr);

# Carp errors from threads::shared calls should complain about caller
our @CARP_NOT = ("threads::shared");

# Predeclarations for internal functions
my ($validate_count, $validate_index);

# Create a new queue possibly pre-populated with items
sub new
{
    my $class = shift;
    my @queue :shared = map { shared_clone($_) } @_;
    return bless(\@queue, $class);
}

# Add items to the tail of a queue
sub enqueue
{
    my $queue = shift;
    lock(@$queue);
    push(@$queue, map { shared_clone($_) } @_)
        and cond_signal(@$queue);
}

# Return a count of the number of items on a queue
sub pending
{
    my $queue = shift;
    lock(@$queue);
    return scalar(@$queue);
}

# Return 1 or more items from the head of a queue, blocking if needed
sub dequeue
{
    my $queue = shift;
    lock(@$queue);

    my $count = @_ ? $validate_count->(shift) : 1;

    # Wait for requisite number of items
    cond_wait(@$queue) until (@$queue >= $count);
    cond_signal(@$queue) if (@$queue > $count);

    # Return single item
    return shift(@$queue) if ($count == 1);

    # Return multiple items
    my @items;
    push(@items, shift(@$queue)) for (1..$count);
    return @items;
}

# Return items from the head of a queue with no blocking
sub dequeue_nb
{
    my $queue = shift;
    lock(@$queue);

    my $count = @_ ? $validate_count->(shift) : 1;

    # Return single item
    return shift(@$queue) if ($count == 1);

    # Return multiple items
    my @items;
    for (1..$count) {
        last if (! @$queue);
        push(@items, shift(@$queue));
    }
    return @items;
}

# Return an item without removing it from a queue
sub peek
{
    my $queue = shift;
    lock(@$queue);
    my $index = @_ ? $validate_index->(shift) : 0;
    return $$queue[$index];
}

# Insert items anywhere into a queue
sub insert
{
    my $queue = shift;
    lock(@$queue);

    my $index = $validate_index->(shift);

    return if (! @_);   # Nothing to insert

    # Support negative indices
    if ($index < 0) {
        $index += @$queue;
        if ($index < 0) {
            $index = 0;
        }
    }

    # Dequeue items from $index onward
    my @tmp;
    while (@$queue > $index) {
        unshift(@tmp, pop(@$queue))
    }

    # Add new items to the queue
    push(@$queue, map { shared_clone($_) } @_);

    # Add previous items back onto the queue
    push(@$queue, @tmp);

    # Soup's up
    cond_signal(@$queue);
}

# Remove items from anywhere in a queue
sub extract
{
    my $queue = shift;
    lock(@$queue);

    my $index = @_ ? $validate_index->(shift) : 0;
    my $count = @_ ? $validate_count->(shift) : 1;

    # Support negative indices
    if ($index < 0) {
        $index += @$queue;
        if ($index < 0) {
            $count += $index;
            return if ($count <= 0);            # Beyond the head of the queue
            return $queue->dequeue_nb($count);  # Extract from the head
        }
    }

    # Dequeue items from $index+$count onward
    my @tmp;
    while (@$queue > ($index+$count)) {
        unshift(@tmp, pop(@$queue))
    }

    # Extract desired items
    my @items;
    unshift(@items, pop(@$queue)) while (@$queue > $index);

    # Add back any removed items
    push(@$queue, @tmp);

    # Return single item
    return $items[0] if ($count == 1);

    # Return multiple items
    return @items;
}

### Internal Functions ###

# Check value of the requested index
$validate_index = sub {
    my $index = shift;

    if (! defined($index) ||
        ! looks_like_number($index) ||
        (int($index) != $index))
    {
        require Carp;
        my ($method) = (caller(1))[3];
        $method =~ s/Thread::Queue:://;
        $index = 'undef' if (! defined($index));
        Carp::croak("Invalid 'index' argument ($index) to '$method' method");
    }

    return $index;
};

# Check value of the requested count
$validate_count = sub {
    my $count = shift;

    if (! defined($count) ||
        ! looks_like_number($count) ||
        (int($count) != $count) ||
        ($count < 1))
    {
        require Carp;
        my ($method) = (caller(1))[3];
        $method =~ s/Thread::Queue:://;
        $count = 'undef' if (! defined($count));
        Carp::croak("Invalid 'count' argument ($count) to '$method' method");
    }

    return $count;
};

1;

=head1 NAME

Thread::Queue - Thread-safe queues

=head1 VERSION

This document describes Thread::Queue version 2.12

=head1 SYNOPSIS

    use strict;
    use warnings;

    use threads;
    use Thread::Queue;

    my $q = Thread::Queue->new();    # A new empty queue

    # Worker thread
    my $thr = threads->create(sub {
                                while (my $item = $q->dequeue()) {
                                    # Do work on $item
                                }
                             })->detach();

    # Send work to the thread
    $q->enqueue($item1, ...);


    # Count of items in the queue
    my $left = $q->pending();

    # Non-blocking dequeue
    if (defined(my $item = $q->dequeue_nb())) {
        # Work on $item
    }

    # Get the second item in the queue without dequeuing anything
    my $item = $q->peek(1);

    # Insert two items into the queue just behind the head
    $q->insert(1, $item1, $item2);

    # Extract the last two items on the queue
    my ($item1, $item2) = $q->extract(-2, 2);

=head1 DESCRIPTION

This module provides thread-safe FIFO queues that can be accessed safely by
any number of threads.

Any data types supported by L<threads::shared> can be passed via queues:

=over

=item Ordinary scalars

=item Array refs

=item Hash refs

=item Scalar refs

=item Objects based on the above

=back

Ordinary scalars are added to queues as they are.

If not already thread-shared, the other complex data types will be cloned
(recursively, if needed, and including any C<bless>ings and read-only
settings) into thread-shared structures before being placed onto a queue.

For example, the following would cause L<Thread::Queue> to create a empty,
shared array reference via C<&shared([])>, copy the elements 'foo', 'bar'
and 'baz' from C<@ary> into it, and then place that shared reference onto
the queue:

    my @ary = qw/foo bar baz/;
    $q->enqueue(\@ary);

However, for the following, the items are already shared, so their references
are added directly to the queue, and no cloning takes place:

    my @ary :shared = qw/foo bar baz/;
    $q->enqueue(\@ary);

    my $obj = &shared({});
    $$obj{'foo'} = 'bar';
    $$obj{'qux'} = 99;
    bless($obj, 'My::Class');
    $q->enqueue($obj);

See L</"LIMITATIONS"> for caveats related to passing objects via queues.

=head1 QUEUE CREATION

=over

=item ->new()

Creates a new empty queue.

=item ->new(LIST)

Creates a new queue pre-populated with the provided list of items.

=back

=head1 BASIC METHODS

The following methods deal with queues on a FIFO basis.

=over

=item ->enqueue(LIST)

Adds a list of items onto the end of the queue.

=item ->dequeue()

=item ->dequeue(COUNT)

Removes the requested number of items (default is 1) from the head of the
queue, and returns them.  If the queue contains fewer than the requested
number of items, then the thread will be blocked until the requisite number
of items are available (i.e., until other threads <enqueue> more items).

=item ->dequeue_nb()

=item ->dequeue_nb(COUNT)

Removes the requested number of items (default is 1) from the head of the
queue, and returns them.  If the queue contains fewer than the requested
number of items, then it immediately (i.e., non-blocking) returns whatever
items there are on the queue.  If the queue is empty, then C<undef> is
returned.

=item ->pending()

Returns the number of items still in the queue.

=back

=head1 ADVANCED METHODS

The following methods can be used to manipulate items anywhere in a queue.

To prevent the contents of a queue from being modified by another thread
while it is being examined and/or changed, L<lock|threads::shared/"lock
VARIABLE"> the queue inside a local block:

    {
        lock($q);   # Keep other threads from changing the queue's contents
        my $item = $q->peek();
        if ($item ...) {
            ...
        }
    }
    # Queue is now unlocked

=over

=item ->peek()

=item ->peek(INDEX)

Returns an item from the queue without dequeuing anything.  Defaults to the
the head of queue (at index position 0) if no index is specified.  Negative
index values are supported as with L<arrays|perldata/"Subscripts"> (i.e., -1
is the end of the queue, -2 is next to last, and so on).

If no items exists at the specified index (i.e., the queue is empty, or the
index is beyond the number of items on the queue), then C<undef> is returned.

Remember, the returned item is not removed from the queue, so manipulating a
C<peek>ed at reference affects the item on the queue.

=item ->insert(INDEX, LIST)

Adds the list of items to the queue at the specified index position (0
is the head of the list).  Any existing items at and beyond that position are
pushed back past the newly added items:

    $q->enqueue(1, 2, 3, 4);
    $q->insert(1, qw/foo bar/);
    # Queue now contains:  1, foo, bar, 2, 3, 4

Specifying an index position greater than the number of items in the queue
just adds the list to the end.

Negative index positions are supported:

    $q->enqueue(1, 2, 3, 4);
    $q->insert(-2, qw/foo bar/);
    # Queue now contains:  1, 2, foo, bar, 3, 4

Specifying a negative index position greater than the number of items in the
queue adds the list to the head of the queue.

=item ->extract()

=item ->extract(INDEX)

=item ->extract(INDEX, COUNT)

Removes and returns the specified number of items (defaults to 1) from the
specified index position in the queue (0 is the head of the queue).  When
called with no arguments, C<extract> operates the same as C<dequeue_nb>.

This method is non-blocking, and will return only as many items as are
available to fulfill the request:

    $q->enqueue(1, 2, 3, 4);
    my $item  = $q->extract(2)     # Returns 3
                                   # Queue now contains:  1, 2, 4
    my @items = $q->extract(1, 3)  # Returns (2, 4)
                                   # Queue now contains:  1

Specifying an index position greater than the number of items in the
queue results in C<undef> or an empty list being returned.

    $q->enqueue('foo');
    my $nada = $q->extract(3)      # Returns undef
    my @nada = $q->extract(1, 3)   # Returns ()

Negative index positions are supported.  Specifying a negative index position
greater than the number of items in the queue may return items from the head
of the queue (similar to C<dequeue_nb>) if the count overlaps the head of the
queue from the specified position (i.e. if queue size + index + count is
greater than zero):

    $q->enqueue(qw/foo bar baz/);
    my @nada = $q->extract(-6, 2);   # Returns ()         - (3+(-6)+2) <= 0
    my @some = $q->extract(-6, 4);   # Returns (foo)      - (3+(-6)+4) > 0
                                     # Queue now contains:  bar, baz
    my @rest = $q->extract(-3, 4);   # Returns (bar, baz) - (2+(-3)+4) > 0

=back

=head1 NOTES

Queues created by L<Thread::Queue> can be used in both threaded and
non-threaded applications.

=head1 LIMITATIONS

Passing objects on queues may not work if the objects' classes do not support
sharing.  See L<threads::shared/"BUGS AND LIMITATIONS"> for more.

Passing array/hash refs that contain objects may not work for Perl prior to
5.10.0.

=head1 SEE ALSO

Thread::Queue Discussion Forum on CPAN:
L<http://www.cpanforum.com/dist/Thread-Queue>

L<threads>, L<threads::shared>

=head1 MAINTAINER

Jerry D. Hedden, S<E<lt>jdhedden AT cpan DOT orgE<gt>>

=head1 LICENSE

This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.

=cut