68 lines
3.0 KiB
Plaintext
68 lines
3.0 KiB
Plaintext
/*
|
|
ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010 Giovanni Di Sirio.
|
|
|
|
This file is part of ChibiOS/RT.
|
|
|
|
ChibiOS/RT is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 3 of the License, or
|
|
(at your option) any later version.
|
|
|
|
ChibiOS/RT is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
GNU General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with this program. If not, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
/**
|
|
* @page article_lifecycle Threads Lifecycle
|
|
* In ChibiOS/RT threads are divided in two categories:
|
|
* - Static threads. The memory used for static threads is allocated at
|
|
* compile time so static threads are always there, there is no management
|
|
* to be done.
|
|
* - Dynamic threads. Dynamic threads are allocated at runtime from one of
|
|
* the available allocators (see @ref heaps, @ref pools).
|
|
* .
|
|
* Dynamic threads create the problem of who is responsible of releasing
|
|
* their memory because a thread cannot dispose its own memory.<br>
|
|
* This is handled in ChibiOS/RT through the mechanism of "thread references",
|
|
* When the @p CH_USE_DYNAMIC option is enabled the threads becomes objects
|
|
* with a reference counter. The memory of a thread, if dynamic, is released
|
|
* when the last reference to the thread is released while the thread is in
|
|
* its @p THD_STATE_FINAL state.<br>
|
|
* The following diagram explains the mechanism:
|
|
* @dot
|
|
digraph example {
|
|
rankdir="LR";
|
|
node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.75", height="0.75"];
|
|
edge [fontname=Helvetica, fontsize=8];
|
|
|
|
init [label="No thread", style="bold"];
|
|
alive [label="Alive"];
|
|
final [label="Terminated"];
|
|
detached [label="Detached", style="bold"];
|
|
|
|
init -> alive [label="chThdCreateX()"];
|
|
alive -> alive [label="chThdAddRef()"];
|
|
alive -> alive [label="chThdRelease()\n[ref > 0]"];
|
|
alive -> detached [label="chThdRelease()\n[ref == 0]"];
|
|
alive -> init [label="chThdWait()\n[ref == 0]"];
|
|
alive -> final [label="chThdExit()\nreturn"];
|
|
final -> final [label="chThdAddRef()"];
|
|
final -> final [label="chThdRelease()\nchThdWait()\n[ref > 0]"];
|
|
final -> init [label="chThdRelease()\nchThdWait()\n[ref == 0]"];
|
|
}
|
|
* @enddot
|
|
* <br>
|
|
* As you can see the simplest way to ensure that the memory is released is
|
|
* that another threads performs a @p chThdWait() on the dynamic thread.<br>
|
|
* If all the references to the threads are released while the thread is
|
|
* still alive then the thread goes in a "detached" state and its memory
|
|
* cannot be recovered unless there is a dedicated task in the system that
|
|
* scans the threads through the @ref registry subsystem and frees the
|
|
* terminated ones.
|
|
*/
|