Hi,
I'm trying to make myself familiar with threads.
However, I encountered some unexpected behaviour of locks/cond_wait I wasn't
able to figure out.
Could someone explain to me what's happening ??
Thanks, Michael
----------------------
#!/usr/bin/perl -w
use threads;
use threads::shared;
share( $x );
share( $y );
sub thread1{
print "1\n";
lock $x;
print "locked x: 1\n";
cond_wait $x;
print "thread1\n";
lock $y;
cond_signal $y;
print "t1\n";
}
sub thread2{
sleep 1;
lock $y;
# {
lock $x;
print "locked x: 2\n";
cond_signal $x;
# }
print "thread2\n";
sleep 1;
cond_wait $y;
print "t2\n";
}
my $t1 = threads->create( "thread1" );
my $t2 = threads->create( "thread2" );
$t1->join;
$t2->join;
print "exit.\n";
---------------------
I expected the script to have a output like:
---
1
locked x: 1
locked x: 2
thread2
thread1
t1
t2
exit.
---
Instead it hangs in the function thread1, at cond_wait $x,
so here's the actual output.
---
1
locked x: 1
locked x: 2
thread2
---
If I uncomment the two brackets of the function thread2, it works again. Which
I cannot understand.
---
sub thread2{
sleep 1;
lock $y;
{
lock $x;
print "locked x: 2\n";
cond_signal $x;
}
print "thread2\n";
sleep 1;
cond_wait $y;
print "t2\n";
}
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