System-wide global variable / semaphore / mutex in C++/Linux?

Question

Is it possible to create a system-wide global variable / semaphore / mutex in C++ on Linux?

Here's the reason: I've got a system that often runs multiple copies of the same software on unrelated data. It's common to have 4 jobs, each running the same software. The software has a small section where it creates a huge graph that takes a lot of memory; outside that section memory usage is moderate.

It so happens sometimes that 2 jobs simultaneously hit the same memory-hungry section and the whole system starts swapping. Thus we want to prevent that by creating something like a critical section mutex between different jobs so that no more than one of them would allocate a lot of memory at a time.

If these were thread of the same job pthread locks would do the job.

What would be a good way to implement such mutex between different jobs?

Answer 1

You can use a named semaphore if you can get all the processes to agree on a common name.

A named semaphore is identified by a name of the form /somename; that is, a null-terminated string of up to NAME_MAX-4 (i.e., 251) characters consisting of an initial slash, followed by one or more characters, none of which are slashes. Two processes can operate on the same named semaphore by passing the same name to sem_open(3).