@node Processes (native threads)
@subsection Processes (native threads)

Process is a primitive representing native thread.

@node Processes dictionary
@subsection Processes dictionary

@cppdef mp_all_processes
@lspdef mp:all-processes

@deftypefun cl_object mp_all_processes ()
@end deftypefun

@defun mp:all-processes

Returns the list of processes associated to running tasks. The list is a
fresh new one and can be destructively modified. However, it may happen
that the output list is not up to date, because some of the tasks have
expired before this copy is returned.

@end defun


@cppdef mp_exit_process
@lspdef mp:exit-process

@deftypefun cl_object mp_exit_process () ecl_attr_noreturn
@end deftypefun

@defun mp:exit-process

When called from a running task, this function immediately causes the
task to finish. When invoked from the main thread, it is equivalent to
invoking @coderef{ext:quit} with exit code 0.

@end defun


@cppdef mp_interrupt_process
@lspdef mp:interrupt-process

@deftypefun cl_object mp_interrupt_process (cl_object process, cl_object function)
@end deftypefun

@defun mp:interrupt-process process function

Interrupt a task. This function sends a signal to a running
@var{process}. When the task is free to process that signal, it will
stop whatever it is doing and execute the given function.

@strong{WARNING:} Use with care! Interrupts can happen anywhere,
except in code regions explicitely protected with
@coderef{mp:without-interrupts}. This can lead to dangerous situations
when interrupting functions which are not thread safe. In particular,
one has to consider:
@itemize
@item Reentrancy: Functions, which usually are not called recursively can be re-entered during execution of the interrupt.
@item Stack unwinding: Non-local jumps like @code{throw} or @code{return-from} in the interrupting code will handle @code{unwind-protect} forms like usual. However, the cleanup forms of an @code{unwind-protect} can still be interrupted. In that case the execution flow will jump to the next @code{unwind-protect}.
@end itemize
Note also that no guarantees are made that functions from the Common
Lisp standard or ECL extensions are interrupt safe (although most of
them will be). In particular, the compiler (@code{compile} and
@code{compile-file} functions), FFI calls and aquire/release functions
for multithreading synchronization objects like mutexes or condition
variables should not be interrupted by @coderef{mp:interrupt-process}.

@exindex Process interruption
Example:

Kill a task that is doing nothing (See @coderef{mp:process-kill}).

@lisp
(flet ((task-to-be-killed ()
         ;; Infinite loop
         (loop (sleep 1))))
  (let ((task (mp:process-run-function 'background #'task-to-be-killed)))
    (sleep 10)
    (mp:interrupt-process task 'mp:exit-process)))
@end lisp

@end defun


@cppdef mp_make_process
@lspdef mp:make-process

@deftypefun cl_object mp_make_process (cl_narg narg, ...)
@end deftypefun

@defun mp:make-process &key name initial-bindings

Create a new thread. This function creates a separate task with a name
set to @var{name} and no function to run. See also
@coderef{mp:process-run-function}. Returns newly created process.

If @var{initial-bindings} is false, the new process inherits local
bindings to special variables (i.e. binding a special variable with
@code{let} or @code{let*}) from the thread that enables it, otherwise
the new thread initially possesses no local bindings.
@end defun


@cppdef mp_process_active_p
@lspdef mp:process-active-p

@deftypefun cl_object mp_process_active_p (cl_object process)
@end deftypefun

@defun mp:process-active-p process

Returns @code{t} when @var{process} is active, @code{nil}
otherwise. Signals an error if @var{process} doesn't designate a valid
process.

@end defun


@cppdef mp_process_enable
@lspdef mp:process-enable

@deftypefun cl_object mp_process_enable (cl_object process)
@end deftypefun

@defun mp:process-enable process

The argument to this function should be a process created by
@coderef{mp:make-process}, which has a function associated as per
@coderef{mp:process-preset} but which is not yet running.  After invoking
this function a new thread will be created in which the associated
function will be executed.  Returns @var{process} if the thread
creation was successful and @code{nil} otherwise.

@exindex Possible implementation of @coderef{mp:process-run-function}:

@lisp
(defun process-run-function (process-name process-function &rest args)
  (let ((process (mp:make-process name)))
    (apply #'mp:process-preset process function args)
    (mp:process-enable process)))
@end lisp
@end defun


@cppdef mp_process_yield
@lspdef mp:process-yield

@deftypefun cl_object mp_process_yield ()
@end deftypefun

@defun mp:process-yield
Yield the processor to other threads.
@end defun


@cppdef mp_process-join
@lspdef mp:process-join

@deftypefun cl_object mp_process_join (cl_object process)
@end deftypefun

@defun mp:process-join process
Suspend current thread until @var{process} exits. Return the result
values of the @var{process} function.
@end defun


@cppdef mp_process_kill
@lspdef mp:process-kill

@deftypefun cl_object mp_process_kill (cl_object process)
@end deftypefun

@defun mp:process-kill process
Try to stop a running task. Killing a process may fail if the task has
disabled interrupts.

@exindex Killing process
Example:

Kill a task that is doing nothing
@lisp
(flet ((task-to-be-killed ()
         ;; Infinite loop
         (loop (sleep 1))))
  (let ((task (mp:process-run-function 'background #'task-to-be-killed)))
    (sleep 10)
    (mp:process-kill task)))
@end lisp
@end defun


@cppdef mp_process_suspend
@lspdef mp:process-suspend

@deftypefun cl_object mp_process_suspend (cl_object process)
@end deftypefun

@defun mp:process-suspend process
Suspend a running @var{process}. May be resumed with
@coderef{mp:process-resume}.

@exindex Suspend and resume process
Example:

@lisp
(flet ((ticking-task ()
         ;; Infinite loop
         (loop
            (sleep 1)
            (print :tick))))
  (print "Running task (one tick per second)")
  (let ((task (mp:process-run-function 'background #'ticking-task)))
    (sleep 5)
    (print "Suspending task for 5 seconds")
    (mp:process-suspend task)
    (sleep 5)
    (print "Resuming task for 5 seconds")
    (mp:process-resume task)
    (sleep 5)
    (print "Killing task")
    (mp:process-kill task)))
@end lisp
@end defun


@cppdef mp_process_resume
@lspdef mp:process-resume

@deftypefun cl_object mp_process_resume (cl_object process)
@end deftypefun

@defun mp:process-resume process
Resumes a suspended @var{process}. See example in
@coderef{mp:process-suspend}.
@end defun


@cppdef mp_process_name
@lspdef mp:process-name

@deftypefun cl_object mp_process_name (cl_object process)
@end deftypefun

@defun mp:process-name process
Returns the name of a @var{process} (if any).
@end defun


@cppdef mp_process_preset
@lspdef mp:process-preset

@deftypefun cl_object mp_process_preset (cl_narg narg, cl_object process, cl_object function, ...)
@end deftypefun

@defun mp:process-preset process function &rest function-args

Associates a @var{function} to call with the arguments
@var{function-args}, with a stopped @var{process}. The function will
be the entry point when the task is enabled in the future.

See @coderef{mp:process-enable} and @coderef{mp:process-run-function}.

@end defun


@cppdef mp_process_run_function
@lspdef mp:process-run-function

@deftypefun cl_object mp_process_run_function (cl_narg narg, cl_object name, cl_object function, ...)
@end deftypefun

@defun mp:process-run-function name function &rest function-args
Create a new process using @coderef{mp:make-process}, associate a function
to it and start it using @coderef{mp:process-preset}.

@exindex mp:process-run-function usage
Example:

@lisp
(flet ((count-numbers (end-number)
         (dotimes (i end-number)
	   (format t "~%;;; Counting: ~i" i)
	   (terpri)
	   (sleep 1))))
  (mp:process-run-function 'counter #'count-numbers 10))
@end lisp
@end defun


@cppdef mp_current_process
@lspdef mp:*current-process*

@deftypefun cl_object mp_current_process ()
@end deftypefun

@defvr Variable {mp:*current-process*}
Returns/holds the current process of a caller.
@end defvr


@cppdef mp_block_signals
@lspdef mp:block-signals

@deftypefun cl_object mp_block_signals ()
@end deftypefun

@defun mp:block-signals
Blocks process for interrupts and returns the previous sigmask.

See @coderef{mp:interrupt-process}.
@end defun


@cppdef mp_restore_signals
@lspdef mp:restore-signals

@deftypefun cl_object mp_restore_signals (cl_object sigmask)
@end deftypefun

@defun mp:restore-signals sigmask
Enables the interrupts from @var{sigmask}.

See @coderef{mp:interrupt-process}.
@end defun


@lspdef mp:without-interrupts
@lspdef mp:allow-with-interrupts
@lspdef mp:with-local-interrupts
@lspdef mp:with-restored-interrupts

@defmac mp:without-interrupts &body body

Executes @var{body} with all deferrable interrupts disabled. Deferrable
interrupts arriving during execution of the @var{body} take effect
after @var{body} has been executed.

Deferrable interrupts include most blockable POSIX signals, and
@coderef{mp:interrupt-process}. Does not interfere with garbage
collection, and unlike in many traditional Lisps using userspace
threads, in ECL @coderef{mp:without-interrupts} does not inhibit
scheduling of other threads.

Binds @coderef{mp:allow-with-interrupts},
@coderef{mp:with-local-interrupts} and
@coderef{mp:with-restored-interrupts} as a local macros.

@coderef{mp:with-restored-interrupts} executes the body with interrupts
enabled if and only if the @coderef{mp:without-interrupts} was in an
environment in which interrupts were allowed.

@coderef{mp:allow-with-interrupts} allows the
@coderef{mp:with-interrupts} to take effect during the dynamic scope of
its body, unless there is an outer @coderef{mp:without-interrupts}
without a corresponding @coderef{mp:allow-with-interrupts}.

@coderef{mp:with-local-interrupts} executes its body with interrupts
enabled provided that there is an @coderef{mp:allow-with-interrupts} for
every @coderef{mp:without-interrupts} surrounding the current one.
@coderef{mp:with-local-interrupts} is equivalent to:

@lisp
(mp:allow-with-interrupts (mp:with-interrupts ...))
@end lisp

Care must be taken not to let either @coderef{mp:allow-with-interrupts}
or @coderef{mp:with-local-interrupts} appear in a function that escapes
from inside the @coderef{mp:without-interrupts} in:

@lisp
(mp:without-interrupts
  ;; The body of the lambda would be executed with WITH-INTERRUPTS allowed
  ;; regardless of the interrupt policy in effect when it is called.
  (lambda () (mp:allow-with-interrupts ...)))

(mp:without-interrupts
  ;; The body of the lambda would be executed with interrupts enabled
  ;; regardless of the interrupt policy in effect when it is called.
  (lambda () (mp:with-local-interrupts ...)))
@end lisp
@end defmac


@lspdef mp:with-interrupts
@defmac mp:with-interrupts &body body
Executes @var{body} with deferrable interrupts conditionally
enabled. If there are pending interrupts they take effect prior to
executing @var{body}.

As interrupts are normally allowed @coderef{mp:with-interrupts} only
makes sense if there is an outer @coderef{mp:without-interrupts} with a
corresponding @coderef{mp:allow-with-interrupts}: interrupts are not
enabled if any outer @coderef{mp:without-interrupts} is not accompanied
by @coderef{mp:allow-with-interrupts}.
@end defmac
