What is the purpose of a dispatch barrier in multithreaded applications?

A dispatch barrier is used to synchronize access to shared resources in multithreaded applications.

Its goal is to ensure that all tasks launched before the barrier complete before the barrier task begins, and that tasks after the barrier only execute after its completion.

This allows:

• Performing write or data modification operations exclusively, without simultaneous reading or writing.
• Guaranteeing the sequence of execution of critical code sections.

For example, in GCD (Grand Central Dispatch), dispatch_barrier_async can be used for writing to a shared resource, while all reads (regular asynchronous tasks) can run in parallel, but the write will be exclusive and will not intersect with other tasks.