2.3. Transferring ownership of a thread

Suppose you want to write a function that creates a thread to run in the background but passes back ownership of the new thread to the calling function rather than waiting for it to complete, or maybe you want to do the reverse: create a thread and pass ownership in to some function that should wait for it to complete. In either case, you need to transfer ownership from one place to another.

This is where the move support of std::thread comes in. As described in the previous section, many resource-owning types in the C++ Standard Library such as std::ifstream and std::unique_ptr are movable but not copyable, and std::thread is one of them. This means that the ownership of a particular thread of execution can be moved between std::thread instances, as in the following example. The example shows the creation of two threads of execution and the transfer of ownership of those threads among three std::thread instances, t1, t2, and t3: