NSCondition

Thread synchronization primitive that combines mutex and condition variable functionality. Provides low-level thread coordination.

Base Class

NSObject

Implemented Protocols

• NSLocking
• MulleObjCThreadSafe

Instance Variables

#ifndef _WIN32
pthread_mutex_t   _lock;       // Mutex for synchronization
pthread_cond_t    _condition;  // Condition variable
#endif

Methods

NSLocking Protocol

• -lock - Acquires the lock
• -unlock - Releases the lock
• -tryLock - Attempts to acquire lock without blocking

Condition Operations

• -signal - Wakes one waiting thread
• -broadcast - Wakes all waiting threads
• -wait - Waits for signal (must be locked)

Properties

• @property name - Condition name (for debugging)
• @property(readonly) mulleIsLocked - Lock state

Usage Example

// Create condition
NSCondition *condition = [[NSCondition alloc] init];

// Producer thread
[condition lock];
// ... modify shared state ...
[condition signal];  // or [condition broadcast];
[condition unlock];

// Consumer thread
[condition lock];
while (!readyToProcess) {
    [condition wait];
}
// ... process shared state ...
[condition unlock];

// Try lock without blocking
if ([condition tryLock]) {
    // ... critical section ...
    [condition unlock];
}

Important Notes

1. Thread Safety
   • Thread-safe by design
   • Requires careful lock/unlock pairing
   • Protects condition state
2. Implementation Details
   • Wraps pthread primitives
   • Combines mutex and condition
   • Supports spurious wakeups
   • Low-level synchronization
3. Usage Guidelines
   • Lock before wait/signal
   • Check conditions in while loop
   • Handle spurious wakeups
   • Avoid deadlocks
4. Best Practices
   • Keep critical sections short
   • Use NSConditionLock if possible
   • Document synchronization protocol
   • Consider higher-level alternatives
5. Common Pitfalls
   • Missing lock/unlock pairs
   • Not checking conditions in loop
   • Incorrect signal timing
   • Deadlock scenarios