18.2 Examples and Caveats

 

The sample kernels in the examples/threads directory (see Section 1.6.1), contain several sample kernels demonstrating the use of the POSIX threads module.

• dphils: A computational example that tests basic POSIX threads operations such as thread creation, mutexes, and conditions. Solves the classic Dining Philosophers problem.
• disktest: A contrived disk thrashing program that tests the interaction between POSIX threads and the NetBSD filesystem (see section 25). A number of threads are created, where each one creates and copies files in varying block sizes.
• disknet: Another contrived program that builds on the disk thrashing program above. Also tested is the interaction bewteen POSIX threads and the BSD network interface. Half of the threads created thrash the disk and the other half connect to a server process and send and receive data blocks. This program achieves reasonable interleaving of work.
• http_proxy: A simplified HTTP proxy daemon that tests the interaction between POSIX threads and the BSD network interface. For each new connection request, three threads are created to manage that connection and forward data between the client and the server.

This small set of test programs clearly does not test every possible combination of components. A larger set of test program is in the works. In addition, not all of the thread-safe adaptors are implemented, so some components cannot be used in a multithreaded environment. For now, the POSIX threads module should be used with caution. Note that these examples are compiled and linked against the multithreaded version of the FreeBSD C library (see Section 13), rather than the minimal C library (Section 9).