This document introduces the concept of Processes in Zircon.
Overview
A Zircon process is an instance of a program, consisting of a set of instructions that are executed by one or more threads, along with a collection of resources the program may use to carry out its objectives and interact with the system.
The kernel manages processes using capabilities called Process Objects. Thread Objects are associated with a particular Process Object, which provides the memory and handles to other kernel objects necessary for I/O and computation by the associated threads.
Every process starts with a single Virtual Memory Address Region (VMAR), the
process root VMAR, that spans the entire user address space
(see zx_process_create()).
The root VMAR may be used directly or subdivided into child VMARs.
VMARs are used to map Virtual Memory Objects (VMOs), which provide the code, data, anonymous, and shared memory pages needed by the program into the address space of the process.
A process stops execution when:
- The last thread in the process is terminated or exits.
- The process calls
zx_process_exit()to terminate itself. - The parent job terminates the process.
- The parent job is destroyed.
Processes and jobs
Processes are owned by jobs, which support grouping one or more processes and sub-jobs into a single entity that manages resource limits and permissions, and also provides lifetime control for the group.
Creating a process requires a handle to a job, which the newly created process becomes a child of. Only processes that have a handle to a job can create a new process or job, effectively restricting which processes may manually create other processes.
Many Fuchsia processes do not have a job handle and must use a mechanism provided by the system, such as the Component Framework, to start another process.
For more information, see jobs.