C++ Concurrent Programming: How to avoid thread starvation and priority inversion?

To avoid thread starvation, you can use fair locks to ensure fair allocation of resources, or set thread priorities. To solve priority inversion, you can use priority inheritance, which temporarily increases the priority of the thread holding the resource; or use lock promotion, which increases the priority of the thread that needs the resource.

C Concurrent programming: Avoid thread starvation and priority inversion

In concurrent programming, thread starvation and priority inversion are common challenges that can lead to deadlocks and uncertainty. This article explores these issues and provides solutions, illustrated with practical examples.

Thread starvation

Thread starvation occurs when a thread cannot obtain the required resources (such as locks and memory) for a long time. This may be caused by other threads accessing the resource first.

Solution strategy:

• Use fair lock: Fair lock ensures that all threads obtain resources fairly and prevents a single thread from holding resources for a long time .
• Set thread priority: Allocate more execution opportunities to high-priority threads to ensure that they are not blocked by low-priority threads.

Priority Inversion

Priority inversion occurs when a low-priority thread holds resources required by a high-priority thread. This may cause high-priority threads to be unable to execute, thereby delaying task completion.

Solution strategy:

• Use priority inheritance: When a thread holds a resource, its priority will be temporarily increased , to prevent low-priority threads from grabbing resources.
• Use lock promotion: When a thread needs to access a resource held by a high-priority thread, it will temporarily increase its priority to quickly obtain the resource.

Practical case

Consider the following scenario:

// Thread 1 (low priority)
void thread1() {
  std::mutex m;
  m.lock();
  // Critical section
  m.unlock();
}

// Thread 2 (high priority)
void thread2() {
  std::mutex m;
  m.lock();
  // Critical section
  m.unlock();
}

Assume that thread2 runs with a higher priority than thread1. If thread1 acquires the lock first and enters the critical section, thread2 may be blocked. When thread1 releases the lock, thread2 may still be unable to acquire the lock because thread1 has a lower priority and will seize the lock again. This causes thread2 to starve.

To solve this problem, priority inheritance can be used:

void set_thread_priority(Thread thread, int priority);

void thread1() {
  std::mutex m;
  m.lock();
  // Critical section

  // Boost thread priority while holding lock
  set_thread_priority(std::this_thread::get_id(), 2);
  m.unlock();
}

Conclusion

By understanding thread starvation and priority inversion and applying appropriate Workaround strategies that can significantly improve the performance and reliability of concurrent code.

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