Priority Inversion - Revision history

Suhridk: /* RTSJ Model */

2012-01-07T01:00:17Z

RTSJ Model

2012-01-07T00:59:03Z

Priority Ceiling Emulation

2012-01-07T00:58:29Z

Priority Inheritance

2012-01-07T00:55:51Z

2012-01-07T00:48:24Z

Priority Ceiling Emulation

2012-01-07T00:45:59Z

Deadlocks

2012-01-07T00:44:00Z

Priority Ceiling Emulation

2012-01-07T00:40:36Z

Priority Ceiling Emulation

2012-01-07T00:26:09Z

Deadlock

2012-01-07T00:25:41Z

Deadlock

@@ Line 27: / Line 27: @@
 ** By default, RTSJ requires simple priority inheritance to occur whenever a SO is blocked waiting for a resource.
-* There is a class called javax.realtime.MonitorControl which specifies the monitor priority control Policy.
+* There is a class called javax.realtime.MonitorControl which specifies the monitor priority control Policy. This can be system wide or per shared object.
 * The PriorityInheritance class extends the MonitorControl class.

← Older revision		Revision as of 00:59, 7 January 2012
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	= Priority Ceiling Emulation =		= Priority Ceiling Emulation =
		+
		+	* Priority ceiling emulation is a form of priority inheritance. However, in this case the low priority thread runs at the highest priority of any thread that might request the lock.
		+	* It acquires this priority IMMEDIATE it locks the lock irrespective of whether anyone is being blocked.

	* Each thread has a static (base) default priority assigned to it.		* Each thread has a static (base) default priority assigned to it.

@@ Line 14: / Line 14: @@
 * If thread p is blocking thread q, then p runs with q's priority.
 == RTSJ Model ==
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 * LP locks x, HP prempts LP and locks y.
 * Now with priority inheritance LP should get HP's priority, but doesnt solve any problems- because LP cant enter y which is held by HP.
 * Deadlock !
 = Priority Ceiling Emulation =

@@ Line 65: / Line 65: @@
 * Whenever a SO calls a method for an object which has PCE in force the RTJVM will check the priority of the caller.
 * If the priority > ceiling priority for the object, CeilingViolation will be thrown.
 [[Category:RealtimeJava]]

@@ Line 45: / Line 45: @@
 * Each resource has a static ceiling value defined - this is the maximum priority of the threads that use it. For e.g if a resource is being used by thread with priority 10,2,1. It's ceiling is 10.
 * A thread has a dynamic (active) priority which is max(its own static priority, ceiling value of any resource it has locked).
-* As a consequence, the thread will only suffer a block at the beginning of its execution. How ? For e.g. if a LP thread starts first and locks a resource, then LP thread gets ceiling value priority of resource and runs to completion, so HP thread waits until then. Once HP thread starts running, then it wont block, because whenever it locks any resource - it runs with max priority possible.
+* As a consequence, the thread will only suffer a block at the beginning of its execution. (As opposed to m blocks in Priority Inheritance)
 * Once the thread starts actually executing,
 ** all the resources it needs must be free;

← Older revision		Revision as of 00:45, 7 January 2012
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	* So if thread wants to access two critical resources - it will access both without pre-emption from any other thread.		* So if thread wants to access two critical resources - it will access both without pre-emption from any other thread.
		+
		+	== Ceiling Violation ==
		+
		+	* Whenever a SO calls a method for an object which has PCE in force the RTJVM will check the priority of the caller.
		+	* If the priority > ceiling priority for the object, CeilingViolation will be thrown.

	[[Category:RealtimeJava]]		[[Category:RealtimeJava]]

← Older revision		Revision as of 00:25, 7 January 2012
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	* Deadlock can still occur with priority inheritance.		* Deadlock can still occur with priority inheritance.
		+
		+	* LP Thread-A wants to use CS's x and y. HP Thread-B wants to use the same CS' x and y.
		+	* LP locks x, HP prempts LP and locks y.
		+	* Now with priority inheritance LP should get HP's priority, but doesnt solve any problems- because LP cant enter y which is held by HP.
		+	* Deadlock !

	[[Category:RealtimeJava]]		[[Category:RealtimeJava]]