1 | package Thread;
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2 |
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3 | use strict;
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4 |
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5 | our($VERSION, $ithreads, $othreads);
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6 |
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7 | BEGIN {
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8 | $VERSION = '2.00';
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9 | use Config;
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10 | $ithreads = $Config{useithreads};
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11 | $othreads = $Config{use5005threads};
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12 | }
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13 |
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14 | require Exporter;
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15 | use XSLoader ();
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16 | our(@ISA, @EXPORT, @EXPORT_OK);
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17 |
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18 | @ISA = qw(Exporter);
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19 |
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20 | BEGIN {
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21 | if ($ithreads) {
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22 | @EXPORT = qw(cond_wait cond_broadcast cond_signal)
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23 | } elsif ($othreads) {
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24 | @EXPORT_OK = qw(cond_signal cond_broadcast cond_wait);
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25 | }
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26 | push @EXPORT_OK, qw(async yield);
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27 | }
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28 |
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29 | =head1 NAME
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30 |
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31 | Thread - manipulate threads in Perl (for old code only)
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32 |
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33 | =head1 CAVEAT
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34 |
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35 | Perl has two thread models.
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36 |
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37 | In Perl 5.005 the thread model was that all data is implicitly shared
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38 | and shared access to data has to be explicitly synchronized.
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39 | This model is called "5005threads".
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40 |
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41 | In Perl 5.6 a new model was introduced in which all is was thread
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42 | local and shared access to data has to be explicitly declared.
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43 | This model is called "ithreads", for "interpreter threads".
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44 |
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45 | In Perl 5.6 the ithreads model was not available as a public API,
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46 | only as an internal API that was available for extension writers,
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47 | and to implement fork() emulation on Win32 platforms.
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48 |
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49 | In Perl 5.8 the ithreads model became available through the C<threads>
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50 | module.
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51 |
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52 | Neither model is configured by default into Perl (except, as mentioned
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53 | above, in Win32 ithreads are always available.) You can see your
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54 | Perl's threading configuration by running C<perl -V> and looking for
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55 | the I<use...threads> variables, or inside script by C<use Config;>
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56 | and testing for C<$Config{use5005threads}> and C<$Config{useithreads}>.
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57 |
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58 | For old code and interim backwards compatibility, the Thread module
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59 | has been reworked to function as a frontend for both 5005threads and
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60 | ithreads.
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61 |
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62 | Note that the compatibility is not complete: because the data sharing
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63 | models are directly opposed, anything to do with data sharing has to
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64 | be thought differently. With the ithreads you must explicitly share()
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65 | variables between the threads.
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66 |
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67 | For new code the use of the C<Thread> module is discouraged and
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68 | the direct use of the C<threads> and C<threads::shared> modules
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69 | is encouraged instead.
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70 |
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71 | Finally, note that there are many known serious problems with the
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72 | 5005threads, one of the least of which is that regular expression
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73 | match variables like $1 are not threadsafe, that is, they easily get
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74 | corrupted by competing threads. Other problems include more insidious
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75 | data corruption and mysterious crashes. You are seriously urged to
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76 | use ithreads instead.
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77 |
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78 | =head1 SYNOPSIS
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79 |
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80 | use Thread;
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81 |
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82 | my $t = Thread->new(\&start_sub, @start_args);
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83 |
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84 | $result = $t->join;
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85 | $result = $t->eval;
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86 | $t->detach;
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87 |
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88 | if ($t->done) {
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89 | $t->join;
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90 | }
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91 |
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92 | if($t->equal($another_thread)) {
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93 | # ...
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94 | }
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95 |
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96 | yield();
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97 |
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98 | my $tid = Thread->self->tid;
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99 |
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100 | lock($scalar);
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101 | lock(@array);
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102 | lock(%hash);
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103 |
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104 | lock(\&sub); # not available with ithreads
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105 |
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106 | $flags = $t->flags; # not available with ithreads
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107 |
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108 | my @list = Thread->list; # not available with ithreads
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109 |
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110 | use Thread 'async';
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111 |
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112 | =head1 DESCRIPTION
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113 |
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114 | The C<Thread> module provides multithreading support for perl.
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115 |
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116 | =head1 FUNCTIONS
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117 |
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118 | =over 8
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119 |
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120 | =item $thread = Thread->new(\&start_sub)
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121 |
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122 | =item $thread = Thread->new(\&start_sub, LIST)
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123 |
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124 | C<new> starts a new thread of execution in the referenced subroutine. The
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125 | optional list is passed as parameters to the subroutine. Execution
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126 | continues in both the subroutine and the code after the C<new> call.
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127 |
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128 | C<Thread->new> returns a thread object representing the newly created
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129 | thread.
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130 |
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131 | =item lock VARIABLE
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132 |
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133 | C<lock> places a lock on a variable until the lock goes out of scope.
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134 |
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135 | If the variable is locked by another thread, the C<lock> call will
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136 | block until it's available. C<lock> is recursive, so multiple calls
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137 | to C<lock> are safe--the variable will remain locked until the
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138 | outermost lock on the variable goes out of scope.
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139 |
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140 | Locks on variables only affect C<lock> calls--they do I<not> affect normal
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141 | access to a variable. (Locks on subs are different, and covered in a bit.)
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142 | If you really, I<really> want locks to block access, then go ahead and tie
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143 | them to something and manage this yourself. This is done on purpose.
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144 | While managing access to variables is a good thing, Perl doesn't force
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145 | you out of its living room...
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146 |
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147 | If a container object, such as a hash or array, is locked, all the
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148 | elements of that container are not locked. For example, if a thread
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149 | does a C<lock @a>, any other thread doing a C<lock($a[12])> won't
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150 | block.
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151 |
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152 | With 5005threads you may also C<lock> a sub, using C<lock &sub>.
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153 | Any calls to that sub from another thread will block until the lock
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154 | is released. This behaviour is not equivalent to declaring the sub
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155 | with the C<locked> attribute. The C<locked> attribute serializes
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156 | access to a subroutine, but allows different threads non-simultaneous
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157 | access. C<lock &sub>, on the other hand, will not allow I<any> other
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158 | thread access for the duration of the lock.
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159 |
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160 | Finally, C<lock> will traverse up references exactly I<one> level.
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161 | C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.
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162 |
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163 | =item async BLOCK;
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164 |
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165 | C<async> creates a thread to execute the block immediately following
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166 | it. This block is treated as an anonymous sub, and so must have a
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167 | semi-colon after the closing brace. Like C<Thread->new>, C<async>
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168 | returns a thread object.
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169 |
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170 | =item Thread->self
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171 |
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172 | The C<Thread-E<gt>self> function returns a thread object that represents
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173 | the thread making the C<Thread-E<gt>self> call.
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174 |
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175 | =item cond_wait VARIABLE
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176 |
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177 | The C<cond_wait> function takes a B<locked> variable as
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178 | a parameter, unlocks the variable, and blocks until another thread
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179 | does a C<cond_signal> or C<cond_broadcast> for that same locked
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180 | variable. The variable that C<cond_wait> blocked on is relocked
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181 | after the C<cond_wait> is satisfied. If there are multiple threads
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182 | C<cond_wait>ing on the same variable, all but one will reblock waiting
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183 | to reaquire the lock on the variable. (So if you're only using
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184 | C<cond_wait> for synchronization, give up the lock as soon as
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185 | possible.)
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186 |
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187 | =item cond_signal VARIABLE
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188 |
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189 | The C<cond_signal> function takes a locked variable as a parameter and
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190 | unblocks one thread that's C<cond_wait>ing on that variable. If more than
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191 | one thread is blocked in a C<cond_wait> on that variable, only one (and
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192 | which one is indeterminate) will be unblocked.
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193 |
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194 | If there are no threads blocked in a C<cond_wait> on the variable,
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195 | the signal is discarded.
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196 |
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197 | =item cond_broadcast VARIABLE
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198 |
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199 | The C<cond_broadcast> function works similarly to C<cond_signal>.
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200 | C<cond_broadcast>, though, will unblock B<all> the threads that are
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201 | blocked in a C<cond_wait> on the locked variable, rather than only
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202 | one.
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203 |
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204 | =item yield
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205 |
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206 | The C<yield> function allows another thread to take control of the
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207 | CPU. The exact results are implementation-dependent.
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208 |
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209 | =back
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210 |
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211 | =head1 METHODS
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212 |
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213 | =over 8
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214 |
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215 | =item join
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216 |
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217 | C<join> waits for a thread to end and returns any values the thread
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218 | exited with. C<join> will block until the thread has ended, though
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219 | it won't block if the thread has already terminated.
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220 |
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221 | If the thread being C<join>ed C<die>d, the error it died with will
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222 | be returned at this time. If you don't want the thread performing
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223 | the C<join> to die as well, you should either wrap the C<join> in
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224 | an C<eval> or use the C<eval> thread method instead of C<join>.
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225 |
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226 | =item eval
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227 |
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228 | The C<eval> method wraps an C<eval> around a C<join>, and so waits for
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229 | a thread to exit, passing along any values the thread might have returned.
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230 | Errors, of course, get placed into C<$@>. (Not available with ithreads.)
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231 |
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232 | =item detach
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233 |
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234 | C<detach> tells a thread that it is never going to be joined i.e.
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235 | that all traces of its existence can be removed once it stops running.
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236 | Errors in detached threads will not be visible anywhere - if you want
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237 | to catch them, you should use $SIG{__DIE__} or something like that.
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238 |
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239 | =item equal
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240 |
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241 | C<equal> tests whether two thread objects represent the same thread and
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242 | returns true if they do.
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243 |
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244 | =item tid
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245 |
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246 | The C<tid> method returns the tid of a thread. The tid is
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247 | a monotonically increasing integer assigned when a thread is
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248 | created. The main thread of a program will have a tid of zero,
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249 | while subsequent threads will have tids assigned starting with one.
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250 |
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251 | =item flags
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252 |
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253 | The C<flags> method returns the flags for the thread. This is the
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254 | integer value corresponding to the internal flags for the thread,
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255 | and the value may not be all that meaningful to you.
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256 | (Not available with ithreads.)
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257 |
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258 | =item done
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259 |
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260 | The C<done> method returns true if the thread you're checking has
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261 | finished, and false otherwise. (Not available with ithreads.)
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262 |
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263 | =back
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264 |
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265 | =head1 LIMITATIONS
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266 |
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267 | The sequence number used to assign tids is a simple integer, and no
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268 | checking is done to make sure the tid isn't currently in use. If a
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269 | program creates more than 2**32 - 1 threads in a single run, threads
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270 | may be assigned duplicate tids. This limitation may be lifted in
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271 | a future version of Perl.
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272 |
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273 | =head1 SEE ALSO
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274 |
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275 | L<threads::shared> (not available with 5005threads)
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276 |
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277 | L<attributes>, L<Thread::Queue>, L<Thread::Semaphore>,
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278 | L<Thread::Specific> (not available with ithreads)
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279 |
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280 | =cut
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281 |
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282 | #
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283 | # Methods
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284 | #
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285 |
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286 | #
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287 | # Exported functions
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288 | #
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289 |
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290 | sub async (&) {
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291 | return Thread->new($_[0]);
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292 | }
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293 |
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294 | sub eval {
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295 | return eval { shift->join; };
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296 | }
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297 |
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298 | sub unimplemented {
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299 | print $_[0], " unimplemented with ",
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300 | $Config{useithreads} ? "ithreads" : "5005threads", "\n";
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301 |
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302 | }
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303 |
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304 | sub unimplement {
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305 | for my $m (@_) {
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306 | no strict 'refs';
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307 | *{"Thread::$m"} = sub { unimplemented $m };
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308 | }
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309 | }
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310 |
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311 | BEGIN {
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312 | if ($ithreads) {
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313 | if ($othreads) {
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314 | require Carp;
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315 | Carp::croak("This Perl has both ithreads and 5005threads (serious malconfiguration)");
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316 | }
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317 | XSLoader::load 'threads';
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318 | for my $m (qw(new join detach yield self tid equal list)) {
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319 | no strict 'refs';
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320 | *{"Thread::$m"} = \&{"threads::$m"};
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321 | }
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322 | require 'threads/shared.pm';
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323 | for my $m (qw(cond_signal cond_broadcast cond_wait)) {
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324 | no strict 'refs';
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325 | *{"Thread::$m"} = \&{"threads::shared::${m}_enabled"};
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326 | }
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327 | # trying to unimplement eval gives redefined warning
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328 | unimplement(qw(done flags));
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329 | } elsif ($othreads) {
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330 | XSLoader::load 'Thread';
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331 | } else {
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332 | require Carp;
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333 | Carp::croak("This Perl has neither ithreads nor 5005threads");
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334 | }
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335 | }
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336 |
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337 | 1;
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