There are two groups of concurrent processes, readers and writers, sharing a file. When two or more reader processes access the shared data at the same time, no side effects will occur, but if a writer process and other processes (reading process or writing process) Access to shared data at the same time may cause data inconsistency errors.

Therefore the requirements are:

1. Allow multiple readers to read files at the same time;


2. Only one writer is allowed to write information in the file;


3. Any writer does not allow other readers or writers to work before completing the writing operation;


4. Before the writer performs the writing operation, all existing readers and writers should be allowed to exit.

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