Producer Consumer Pattern

Producer-Consumer Pattern — a fundamental concurrency pattern where producer threads generate data and consumer threads process it, communicating through a shared buffer.

Architecture

[Producer 1] →→
[Producer 2] →→  [Shared Buffer/Queue]  →→ [Consumer 1]
[Producer 3] →→                          →→ [Consumer 2]

Bounded Buffer Implementation

• Fixed-size queue (ring buffer) between producers and consumers
• Producers block when buffer is full (back-pressure)
• Consumers block when buffer is empty (no work)
• Synchronization: Mutex + two condition variables (not_full, not_empty)

Benefits

• Decoupling: Producers and consumers run at different speeds
• Buffering: Absorbs bursts in production/consumption rates
• Scalability: Add producers or consumers independently

Lock-Free Variants

• SPSC (Single-Producer Single-Consumer): Ring buffer with atomic head/tail pointers — no locks needed. Fastest option when topology matches
• MPMC (Multi-Producer Multi-Consumer): More complex, often uses CAS. Examples: Java ConcurrentLinkedQueue, Disruptor

Common Applications

• Web server: Accept thread (producer) → request queue → worker threads (consumers)
• Pipeline processing: Each stage is consumer of previous, producer for next
• Logging: Application threads produce log entries → log writer consumes

Producer-consumer is ubiquitous — it appears in virtually every concurrent system from operating systems to web servers.