Interprocess Mutex In Perl - perl

Question

I have a Perl CGI program that executes under mod_perl. Within the program, I would like to prevent a resource from accessing by multiple processes at the same time.
# Semaphore Initialization Code
# 10023 is unique id, and this id will be same across different apache process.
# 1, Only one semaphore being created.
# 0722, as all process will be execute under apache account. Hence, they will all having '7' privilege.
my $sem = new IPC::Semaphore(10023, 1, 0722 | IPC_CREAT); # Code(1)
# Set 0th (one and only one) semaphore's value to 1, As I want to use this semaphore as mutex.
$sem->setval(0, 1); # Code(2)
The problem is :
How can I make Code(1) create a new semaphore ONLY when the semaphore if the 10023 id has never being created before, either by same process or other processes?
How can I execute Code(2) ONLY the first time I create the semaphore with 10023 id? A semaphore shall be only initialized ONE TIME.
Another approach is to create an empty file for locking purpose. However, this will end up of having thousands of temporary files.
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Answer 1

Adding the IPC_EXCL flag causes the underlying semget to either create a new semaphore or fail. You can use this to get the effect you want.
This should work for you:
#Attempt to create (but not get existing) semaphore
my $sem = IPC::Semaphore->new(10023, 1, 0722 | IPC_CREAT | IPC_EXCL);
if ($sem) {
#success, semaphore created, proceed to set.
print "new semaphore\n";
$sem->setval(0, 1);
}
else {
#obtain the semaphore normally
print "existing semaphore\n";
$sem = IPC::Semaphore->new(10023, 1, 0722); #no IPC_CREAT here
die "could not obtain semaphore?" unless $sem;
}