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|  How to Fix Deadlocks: Step-by-Step Guide

How to Fix Deadlocks: Step-by-Step Guide

October 14, 2024

Discover a simple step-by-step guide tailored for firmware developers using C to effectively resolve deadlocks and ensure seamless performance.

How to Fix Deadlocks: Step-by-Step Guide

 

Understand Deadlocks

  • Identify sections of the code where multiple threads acquire locks. A deadlock occurs when two or more threads wait indefinitely for a set of locks held by each other.
  • Be aware of the four conditions that can lead to a deadlock: mutual exclusion, hold and wait, no preemption, and circular wait.

 

Use Lock Hierarchy

  • Establish a strict ordering of lock acquisition. Ensure every part of the program adheres to this ordering to prevent circular wait.
  • Example: If multiple locks need to be acquired (Lock A then Lock B), enforce that ordering everywhere in your code.
  • pthread_mutex_lock(&lockA);
    pthread_mutex_lock(&lockB);
    /_ Perform critical section actions _/
    pthread_mutex_unlock(&lockB);
    pthread_mutex_unlock(&lockA);
    

 

Timeout and Retry

  • Implement timeout for lock acquisition. If a lock cannot be acquired within a certain time, release any other locks already held and retry.
  • This approach can help break circular waits.
  • struct timespec timeout;
    clock_gettime(CLOCK_REALTIME, &timeout);
    timeout.tv\_sec += 1; // wait for 1 second
    
    

    if (pthread_mutex_timedlock(&lockA, &timeout) == 0) {
    if (pthread_mutex_timedlock(&lockB, &timeout) == 0) {
    /_ Perform critical section actions _/
    pthread_mutex_unlock(&lockB);
    }
    pthread_mutex_unlock(&lockA);
    }


 

Use Try-locks

  • Attempt to acquire locks using non-blocking variants like try-lock. If unable to acquire all required locks, release those acquired and try again later.
  • This reduces the chances of contributing to a deadlock.
  • if (pthread_mutex_trylock(&lockA) == 0) {
      if (pthread_mutex_trylock(&lockB) == 0) {
          /_ Perform critical section actions _/
          pthread_mutex_unlock(&lockB);
      } else {
          pthread_mutex_unlock(&lockA);
      }
    }
    

 

Use Deadlock Detection

  • Implement a mechanism to detect deadlocks at runtime. This involves periodically checking for threads in waiting states due to lock acquisition failures.
  • If detected, attempt recovery through preemption or by breaking the circular wait.

 

Minimize Lock Usage

  • Reduce the scope and number of locks. Smaller critical sections decrease contention and likelihood of deadlocks.
  • Consider single lock designs (coarse-grained locks) where feasible, as they simplify lock management.

 

Analyze with Debug Tools

  • Utilize tools like thread analyzers or debuggers to trace lock acquisition order and identify potential deadlocks in your firmware.
  • Tools specific to an OS or environment can automatically check and alert about possible deadlock situations.

 

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