thread - runnable / computation entity




The thread object is the construct that represents a time-shared CPU execution context. Thread objects live associated to a particular Process Object, which provides the memory and the handles to other objects necessary for I/O and computation.


Threads are created by calling zx_thread_create(), but only start executing when either zx_thread_start() or zx_process_start() are called. Both syscalls take as an argument the entrypoint of the initial routine to execute.

The thread passed to zx_process_start() should be the first thread to start execution on a process.

A thread terminates execution:

Returning from the entrypoint routine does not terminate execution. The last action of the entrypoint should be to call zx_thread_exit() or one of the above mentioned _exit() variants.

Closing the last handle to a thread does not terminate execution. In order to forcefully kill a thread for which there is no available handle, use zx_object_get_child() to obtain a handle to the thread. This method is strongly discouraged. Killing a thread that is executing might leave the process in a corrupt state.

Fuchsia native threads are always detached. That is, there is no join() operation needed to do a clean termination. However, some runtimes above the kernel, such as C11 or POSIX might require threads to be joined.


Threads provide the following signals:


When a thread is started ZX_THREAD_RUNNING is asserted. When it is suspended ZX_THREAD_RUNNING is deasserted, and ZX_THREAD_SUSPENDED is asserted. When the thread is resumed ZX_THREAD_SUSPENDED is deasserted and ZX_THREAD_RUNNING is asserted. When a thread terminates both ZX_THREAD_RUNNING and ZX_THREAD_SUSPENDED are deasserted and ZX_THREAD_TERMINATED is asserted.

Note that signals are OR'd into the state maintained by the zx_object_wait_*() family of functions thus you may see any combination of requested signals when they return.