Conditions and solutions of deadlock

Multiple threads competing for resources wait for each other , The phenomenon that causes permanent blocking is called deadlock

Conditions for Deadlock

1. Mutual exclusivity ： Shared resources can only be occupied by one thread

2. To possess and wait for ： Threads T Shared resources have been obtained A, Waiting to share resources B Not released when A

3. Do not take ： Other threads cannot forcibly occupy T Resources in possession

4. Cycle and wait ： Threads T1 Wait for thread T2 Resources in possession , Threads T2 Wait for thread T1 Resources in possession

Crack deadlock

There are three conditions except mutex for the condition of breaking deadlock , as follows ：

1. damage “ Occupy and wait ” Conditions , You can apply for all resources at once , So there is no waiting .

2. damage “ Do not take ” Conditions , When a thread occupying some resources further requests other resources , If the application does not arrive , Can actively release the resources it occupies , In this way, we can't seize this condition and destroy .

3. damage “ Loop waiting for ” Conditions , It can be prevented by applying resources in sequence . The so-called sequential application , Resources are in linear order
Of , When applying, you can first apply for a resource with a small serial number , And then apply for a large number of resources , In this way, after linearization, there will be no cycle
了 .