tornado.process — Utilities for multiple processes¶
Utilities for working with multiple processes, including both forking the server into multiple processes and managing subprocesses.
Returns the number of processors on this machine.
Starts multiple worker processes.
num_processesis None or <= 0, we detect the number of cores available on this machine and fork that number of child processes. If
num_processesis given and > 0, we fork that specific number of sub-processes.
Since we use processes and not threads, there is no shared memory between any server code.
Note that multiple processes are not compatible with the autoreload module (or the
tornado.web.Applicationwhich defaults to True when
debug=True). When using multiple processes, no IOLoops can be created or referenced until after the call to
In each child process,
fork_processesreturns its task id, a number between 0 and
num_processes. Processes that exit abnormally (due to a signal or non-zero exit status) are restarted with the same id (up to
max_restartstimes). In the parent process,
fork_processesreturns None if all child processes have exited normally, but will otherwise only exit by throwing an exception.
Returns the current task id, if any.
Returns None if this process was not created by
subprocess.Popenwith IOStream support.
The constructor is the same as
subprocess.Popenwith the following additions:
stderrmay have the value
tornado.process.Subprocess.STREAM, which will make the corresponding attribute of the resulting Subprocess a
- A new keyword argument
io_loopmay be used to pass in an IOLoop.
callbackwhen this process exits.
The callback takes one argument, the return code of the process.
This method uses a
SIGCHILDhandler, which is a global setting and may conflict if you have other libraries trying to handle the same signal. If you are using more than one
IOLoopit may be necessary to call
Subprocess.initializefirst to designate one
IOLoopto run the signal handlers.
In many cases a close callback on the stdout or stderr streams can be used as an alternative to an exit callback if the signal handler is causing a problem.
The signal handler is run on an
IOLoopto avoid locking issues. Note that the
IOLoopused for signal handling need not be the same one used by individual Subprocess objects (as long as the
IOLoopsare each running in separate threads).