starpu-max/doc/doxygen/chapters/api/explicit_dependencies.doxy

/*
 * This file is part of the StarPU Handbook.
 * Copyright (C) 2009--2011  Universit@'e de Bordeaux 1
 * Copyright (C) 2010, 2011, 2012, 2013  Centre National de la Recherche Scientifique
 * Copyright (C) 2011, 2012 Institut National de Recherche en Informatique et Automatique
 * See the file version.doxy for copying conditions.
 */

/*! \defgroup API_Explicit_Dependencies Explicit Dependencies

\fn void starpu_task_declare_deps_array(struct starpu_task *task, unsigned ndeps, struct starpu_task *task_array[])
\ingroup API_Explicit_Dependencies
Declare task dependencies between a \p task and an array of
tasks of length \p ndeps. This function must be called prior to the
submission of the task, but it may called after the submission or the
execution of the tasks in the array, provided the tasks are still
valid (i.e. they were not automatically destroyed). Calling this
function on a task that was already submitted or with an entry of
\p task_array that is no longer a valid task results in an undefined
behaviour. If \p ndeps is 0, no dependency is added. It is possible to
call starpu_task_declare_deps_array() several times on the same task,
in this case, the dependencies are added. It is possible to have
redundancy in the task dependencies.

\typedef starpu_tag_t
\ingroup API_Explicit_Dependencies
This type defines a task logical identifer. It is possible to
associate a task with a unique <em>tag</em> chosen by the application,
and to express dependencies between tasks by the means of those tags.
To do so, fill the field starpu_task::tag_id with a tag number (can be
arbitrary) and set the field starpu_task::use_tag to 1. If
starpu_tag_declare_deps() is called with this tag number, the task
will not be started until the tasks which holds the declared
dependency tags are completed.

\fn void starpu_tag_declare_deps(starpu_tag_t id, unsigned ndeps, ...)
\ingroup API_Explicit_Dependencies
Specify the dependencies of the task identified by tag \p id.
The first argument specifies the tag which is configured, the second
argument gives the number of tag(s) on which \p id depends. The
following arguments are the tags which have to be terminated to unlock
the task. This function must be called before the associated task is
submitted to StarPU with starpu_task_submit().

<b>WARNING! Use with caution</b>. Because of the variable arity of
starpu_tag_declare_deps(), note that the last arguments must be of
type starpu_tag_t : constant values typically need to be explicitly
casted. Otherwise, due to integer sizes and argument passing on the
stack, the C compiler might consider the tag <c>0x200000003</c>
instead of <c>0x2</c> and <c>0x3</c> when calling
<c>starpu_tag_declare_deps(0x1, 2, 0x2, 0x3)</c>. Using the
starpu_tag_declare_deps_array() function avoids this hazard.

\code{.c}
/*  Tag 0x1 depends on tags 0x32 and 0x52 */
starpu_tag_declare_deps((starpu_tag_t)0x1, 2, (starpu_tag_t)0x32, (starpu_tag_t)0x52);
\endcode

\fn void starpu_tag_declare_deps_array(starpu_tag_t id, unsigned ndeps, starpu_tag_t *array)
\ingroup API_Explicit_Dependencies
This function is similar to starpu_tag_declare_deps(), except
that its does not take a variable number of arguments but an array of
tags of size \p ndeps.

\code{.c}
/*  Tag 0x1 depends on tags 0x32 and 0x52 */
starpu_tag_t tag_array[2] = {0x32, 0x52};
starpu_tag_declare_deps_array((starpu_tag_t)0x1, 2, tag_array);
\endcode

\fn int starpu_tag_wait(starpu_tag_t id)
\ingroup API_Explicit_Dependencies
This function blocks until the task associated to tag \p id has
been executed. This is a blocking call which must therefore not be
called within tasks or callbacks, but only from the application
directly. It is possible to synchronize with the same tag multiple
times, as long as the starpu_tag_remove() function is not called. Note
that it is still possible to synchronize with a tag associated to a
task for which the strucuture starpu_task was freed (e.g. if the field
starpu_task::destroy was enabled).

\fn int starpu_tag_wait_array(unsigned ntags, starpu_tag_t *id)
\ingroup API_Explicit_Dependencies
This function is similar to starpu_tag_wait() except that it
blocks until all the \p ntags tags contained in the array \p id are
terminated.

\fn void starpu_tag_restart(starpu_tag_t id)
\ingroup API_Explicit_Dependencies
This function can be used to clear the <em>already
notified</em> status of a tag which is not associated with a task.
Before that, calling starpu_tag_notify_from_apps() again will not
notify the successors. After that, the next call to
starpu_tag_notify_from_apps() will notify the successors.

\fn void starpu_tag_remove(starpu_tag_t id)
\ingroup API_Explicit_Dependencies
This function releases the resources associated to tag \p id.
It can be called once the corresponding task has been executed and
when there is no other tag that depend on this tag anymore.

\fn void starpu_tag_notify_from_apps(starpu_tag_t id)
\ingroup API_Explicit_Dependencies
This function explicitly unlocks tag \p id. It may be useful in
the case of applications which execute part of their computation
outside StarPU tasks (e.g. third-party libraries). It is also provided
as a convenient tool for the programmer, for instance to entirely
construct the task DAG before actually giving StarPU the opportunity
to execute the tasks. When called several times on the same tag,
notification will be done only on first call, thus implementing "OR"
dependencies, until the tag is restarted using starpu_tag_restart().

*/