Although the queries _SC_NPROCESSORS_CONF and _SC_NPROCESSORS_ONLN provide a way for a class of "heavy-load" application to estimate the optimal number of threads that can be created to maximize throughput, real-world environments have complications that affect the actual efficiency that can be achieved. For example:

• There may be more than one "heavy-load" application running on the system.


• The system may be on battery power, and applications should co-ordinate with the system to ensure that a long-running task can pause, resume, and successfully complete even in the event of a power outage.

In case a portable "heavy-load" application wants to avoid the use of extensions, its developers may wish to create threads based on the logical partition of the long-running task, or utilize heuristics such as the ratio between CPU time and real time.