6.6 Summary

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Operating systems provide concurrency mechanisms that manage multiple processes on an end system and manage multiple threads within a process. Any decent general-purpose OS allows multiple processes to run concurrently. Modern general-purpose and real-time operating systems also allow multiple threads to run concurrently. When used in conjunction with the appropriate patterns and application configurations, concurrency helps to improve performance and simplify program structure.

The concurrency wrapper facade classes provided by ACE are described in the following four chapters:

• Chapter 7 describes ACE classes for synchronous event demultiplexing .

• Chapter 8 describes ACE classes for OS process mechanisms.

• Chapter 9 describes ACE classes for OS threading mechanisms.

• Chapter 10 describes ACE classes for OS synchronization mechanisms.

Throughout these four chapters we'll examine how ACE uses C++ features and the Wrapper Facade pattern to overcome problems with native OS concurrency APIs and improve the functionality, portability, and robustness of concurrent networked applications. Where appropriate, we'll show ACE concurrency wrapper facade implementations to illustrate how they are mapped onto underlying OS concurrency mechanisms. We also point out where the features of OS platforms differ and how ACE shields developers from these differences.

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