I think choroba was suggesting this (untested):
$sem = IPC::Semaphore->new( 4321, 1, S_IRUSR | S_IWUSR | IPC_CREAT | I
+PC_EXCL );
if ( $sem ) {
# New semaphore
print "Semaphore created\n";
$sem->setval(0,1);
print "Semaphore initialised\n";
} else {
# Semaphore already exists so just open it
print "Semaphore already exists - just open it\n";
$sem = IPC::Semaphore->new( 4321, 1, S_IRUSR | S_IWUSR );
+ );
}
print "Locking other threads\n";
$sem->op(0, -1, SEM_UNDO);
But there is still a race condition, where the second process can attach to and use the semaphore after the first process creates it and before the first process initializes it.
-
Are you posting in the right place? Check out Where do I post X? to know for sure.
-
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big>
<blockquote> <br /> <dd>
<dl> <dt> <em> <font>
<h1> <h2> <h3> <h4>
<h5> <h6> <hr /> <i>
<li> <nbsp> <ol> <p>
<small> <strike> <strong>
<sub> <sup> <table>
<td> <th> <tr> <tt>
<u> <ul>
-
Snippets of code should be wrapped in
<code> tags not
<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
intervention).
-
Want more info? How to link
or How to display code and escape characters
are good places to start.
|