C++ Development Notes: Avoid Deadlock Problems in C++ Code

C development considerations: Avoid deadlock problems in C code

Introduction:
In C development, deadlock (Deadlock) is a very common problem problems, which can lead to serious consequences such as unresponsiveness and crash of the program. Therefore, when we write C code, we must pay special attention to avoiding the occurrence of deadlock. This article will introduce some common deadlock problems and how to avoid deadlocks in C code.

1. What is deadlock?
Deadlock refers to a state in which two or more processes (threads) are waiting for each other for resources already held by the other party, resulting in the inability to continue execution. In C, deadlock usually occurs in multi-threaded programs. When two or more threads depend on each other and wait for each other to release resources, deadlock problems may occur.

2. Causes of deadlock

1. Mutual exclusion: When multiple threads need to occupy the same resource, a mutex lock (Mutex) is used to protect resource access, but If multiple threads hold multiple mutex locks at the same time and wait for each other to release a resource, a deadlock will occur.
2. Competition conditions: When multiple threads compete for the same resource at the same time, if there is no good scheduling mechanism between threads, it will lead to an infinite loop of competing for resources, resulting in a deadlock.
3. Inalienable resources: When a thread holds some inalienable resources, and other threads need these resources to continue execution, but the thread cannot actively release these resources, a deadlock will occur.

3. How to avoid deadlock?

1. Avoid nested locks: In C, it is not recommended to nest multiple locks, which can easily lead to deadlock. Therefore, avoid holding multiple locks at the same time in your code and ensure that each lock is released in time.
2. Acquire locks in order: When multiple threads need to access multiple resources at the same time, deadlock can be avoided by acquiring locks in a specific order. For example, you can acquire locks in order of resource numbers to avoid cyclic waiting.
3. Set the timeout mechanism: When using a mutex, you can set a certain timeout. When waiting to acquire the lock, if the waiting time exceeds a certain threshold, the operation of acquiring the lock will be actively abandoned to avoid waiting. Deadlock caused by too long time.
4. Use read-write lock: If the resource can be read by multiple threads at the same time but can only be written by a single thread, you can use a read-write lock (ReadWriteLock) for optimization. Read-write locks can allow multiple threads to read resources at the same time, but the lock will be acquired exclusively when writing, avoiding read-write conflicts.
5. Use inalienable resources with caution: Try to avoid threads holding inalienable resources. If you really need to use inalienable resources, you can consider setting up a reasonable timeout mechanism to ensure that the resources can be released in time.

Conclusion:
Deadlock is a common problem in C development, but through reasonable design and coding, we can avoid or minimize the occurrence of deadlock. When writing C code, pay attention to techniques such as avoiding nested locks, acquiring locks in order, setting a timeout mechanism, and using read-write locks to reduce the risk of deadlock. Only through continuous learning and practice can we better understand and solve various problems in C development and improve the performance and stability of the program.

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