Assignment name: process_communication
Expected files: process_communication.c
Allowed functions: memset, printf, malloc, free, write, fork, exit, waitpid,
                    sem_open, sem_close, sem_post, sem_wait, sem_unlink,
                    usleep, gettimeofday
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Implement a producer-consumer pattern using processes and semaphores:
1. Create 2 semaphores: one for empty slots (init: 5) and one for filled slots (init: 0)
2. Launch 2 producer processes and 2 consumer processes
3. Producers "produce" items (increment a counter) and signal consumers
4. Consumers wait for items, "consume" them, and signal producers
5. Each process performs 10 operations
6. Use a third semaphore to protect the shared counter (mutual exclusion)

Since processes don't share memory, print actions instead of actually sharing data:
- Producer: "Producer <id>: Produced item <n> (empty slots: <count>)"
- Consumer: "Consumer <id>: Consumed item <n> (filled slots: <count>)"

Parent waits for all children and cleans up semaphores.

Usage: `./process_communication`

Hint: This demonstrates how semaphores coordinate processes (like mutexes for threads).
You need 3 semaphores: empty slots, filled slots, and mutex for critical sections.
The pattern is similar to producer_consumer but with processes instead of threads.
Since processes don't share memory, focus on demonstrating synchronization patterns.
sem_wait() on empty before producing, sem_post() on filled after producing.