From 508b7bc93297fcb74af43b11b1435aa96add3c85 Mon Sep 17 00:00:00 2001
From: gdisirio <gdisirio@35acf78f-673a-0410-8e92-d51de3d6d3f4>
Date: Thu, 25 Feb 2010 16:48:00 +0000
Subject: git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@1675
 35acf78f-673a-0410-8e92-d51de3d6d3f4

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 docs/src/lifecycle.dox | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++
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diff --git a/docs/src/lifecycle.dox b/docs/src/lifecycle.dox
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+/*
+    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.
+ */
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