# Algorithms¶

Most parallel algorithms provided by oneAPI Threading Building Blocks are generic. They operate on all types that model the necessary concepts. Parallel algorithms may be nested. For example, the body of a parallel_for can invoke another parallel_for.

Caution

When the body of an outer parallel algorithm invokes another parallel algorithm, it may cause the outer body to be re-entered for a different iteration of the outer algorithm.

For example, if the outer body holds a global lock while calling an inner parallel algorithm, the body will deadlock if the re-entrant invocation attempts to acquire the same global lock. This ill-formed example is a special case of a general rule that code should not hold a lock while calling code written by another author.