Question

I noticed that boost does not seem to support semaphores. What’s the easiest way to achieve a similar effect?

Answer 1

You either need Boost Interprocess semaphore or Boost Thread synchronization primitives.

Mutex/Lock and condition are primitives that are commonly used to synchronize access to shared resources across multiple threads of a single process. There are exclusive, readers-writer and recursive/reentrant types of mutexes. Mutex, in other words, is an exclusive lock. Condition is used to achieve atomicity when you need to unlock the mutex and wait for object to change. When you start waiting on a condition, it unlocks the mutex and guarantees than unlock + call to wait is atomic and no other threads can modify a resource between those two operations.

Semaphore, on another case, is a mix of condition and mutex, and is used for exactly the same purpose but to synchronize access across processes.

See Mutex vs Semaphore.

There is also such thing as non-blocking/lock-free synchronization that is becoming very popular these days. I personally use it in high-frequency trading applications when amount of data is relatively very large and low latency does matter a lot.

In your case, I assume 5 philosophers can have a dinner inside a single process with 5 threads. In that case you have to use a mutex, not a semaphore. You might or might not use condition though. It depends on what exactly and how exactly you want to implement that dining procedure.

I am not sure how to describe it better as I will end up writing a book about it. So I’d recommend you find some book that is already written to understand the basic concepts. Once you know basics, you can use APIs/libraries/frameworks like POSIX threads, Boost Interprocess or Thread, ACE or even non-blocking algorithms to achieve what you want.

Good luck!