Advanced Programming in the UNIX Environment: Second Edition [Electronic resources] نسخه متنی

12.2. Thread Limits

We discussed the sysconf function in Section 2.5.4. The Single UNIX Specification defines several limits associated with the operation of threads, which we didn't show in Figure 2.10. As with other system limits, the thread limits can be queried using sysconf. Section 12.6)

As with the other limits reported by sysconf, use of these limits is intended to promote application portability among different operating system implementations. For example, if your application requires that you create four threads for every file you manage, you might have to limit the number of files you can manage concurrently if the system won't let you create enough threads.

Figure 12.2 shows the values of the thread limits for the four implementations described in this book. When the implementation doesn't define the corresponding sysconf symbol (starting with _SC_), "no symbol" is listed. If the implementation's limit is indeterminate, "no limit" is listed. This doesn't mean that the value is unlimited, however. An "unsupported" entry means that the implementation defines the corresponding sysconf limit symbol, but the sysconf function doesn't recognize it.

Note that although an implementation may not provide access to these limits, that doesn't mean that the limits don't exist. It just means that the implementation doesn't provide us with a way to get at them using sysconf.