The threads library allows concurrent programming in Objective Caml.
It provides multiple threads of control (also called lightweight
processes) that execute concurrently in the same memory space. Threads
communicate by in-place modification of shared data structures, or by
sending and receiving data on communication channels.
The threads library is implemented by time-sharing on a single
processor. It will not take advantage of multi-processor machines.
Using this library will therefore never make programs run
faster. However, many programs are easier to write when structured as
several communicating processes.
Two implementations of the threads library are available, depending
on the capabilities of the operating system:
-
System threads. This implementation builds on the OS-provided threads
facilities: POSIX 1003.1c threads for Unix, and Win32 threads for
Windows. When available, system threads support both bytecode and
native-code programs.
- VM-level threads. This implementation performs time-sharing and
context switching at the level of the OCaml virtual machine (bytecode
interpreter). It is available on Unix systems, and supports only
bytecode programs. It cannot be used with native-code programs.
Programs that use system threads must be linked as follows:
ocamlc -thread other options threads.cma other files
ocamlopt -thread other options threads.cmxa other files
All object files on the command line must also have been compiled with
the -thread option (see chapter 8).
Programs that use VM-level threads must be compiled with the -vmthread
option to ocamlc (see chapter 8), and be linked as follows:
ocamlc -vmthread other options threads.cma other files