What are the reasons for system deadlock?

The reasons for deadlock in the system include mutual exclusion conditions, request and hold conditions, inevitability conditions and circular waiting conditions. Detailed introduction: 1. Mutually exclusive conditions, multiple threads need to access certain shared resources at the same time, and these resources can only be occupied by one thread at a time. If one thread occupies a certain resource, other threads must wait for the resource to be released; 2 , Request and hold conditions. While a thread holds a certain resource, it also requests resources held by other threads. If these resources are occupied by other threads, it will cause the thread to wait; 3. Inevitability conditions, etc.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

Deadlock refers to a state in which two or more threads wait for each other to release resources in a multi-threaded environment, causing the program to be unable to continue execution. Deadlock is a common problem in concurrent programming, which can lead to system performance degradation or even crash. Below I will explain the causes of deadlock in detail.

The reasons for deadlock usually include the following aspects:

1. Mutually exclusive conditions: Multiple threads need to access certain shared resources at the same time, and these resources Can only be occupied by one thread at a time. If a thread occupies a resource, other threads must wait for the resource to be released.

2. Request and hold conditions: While holding a certain resource, a thread requests resources held by other threads. If these resources are occupied by other threads, the thread will wait.

3. Inevitability condition: Resources that have been allocated to a thread cannot be preempted by other threads and can only be released by the thread that owns it.

4. Circular waiting conditions: A circular waiting relationship is formed between multiple threads, and each thread is waiting for the resources held by the next thread.

When the above four conditions are met at the same time, deadlock may occur. The following is a simple example to illustrate the cause of deadlock:

Suppose there are two threads A and B, which hold resource X and resource Y respectively, and they both need to obtain the resources held by the other party.

When thread A executes to a critical section, it needs to obtain resource Y, but it is found that resource Y has been occupied by thread B, so thread A enters the waiting state and releases resource X.

At the same time, when thread B executes to a certain critical section, it needs to obtain resource X, but it is found that resource X has been occupied by thread A, so thread B enters the waiting state and releases resource Y.

In this way, thread A and thread B wait for each other to release resources, resulting in a deadlock.

In order to avoid the occurrence of deadlock, we can adopt the following strategies:

1. Avoid using multiple locks: try to reduce simultaneous requests for multiple resources and consider refactoring the code , merge multiple locks into one lock.

2. Acquire locks in order: If you must acquire multiple locks at the same time, you can acquire locks in a fixed order to avoid deadlock caused by different threads acquiring locks in different orders.

3. Set the timeout: For some unavoidable situations, you can set the timeout. After waiting for more than a certain period of time, give up acquiring the lock and perform other processing.

4. Deadlock detection and recovery: You can use the deadlock detection algorithm to detect the occurrence of deadlock and take appropriate measures to recover, such as terminating a thread or rolling back the operation.

5. Reasonably design resource allocation strategies: When designing the system, allocate resources reasonably to avoid cyclic waiting.

In summary, deadlock occurs because multiple threads are waiting for each other to release resources, causing the program to be unable to continue execution. To avoid deadlock, you need to pay attention to mutual exclusion conditions, request and hold conditions, inevitability conditions and circular waiting conditions, and adopt corresponding strategies to prevent and deal with the occurrence of deadlocks.

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