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--- at-m42:lecture9 [2009/04/15 17:32] – eechris
+++ at-m42:lecture9 [2011/01/14 12:45] (current) – external edit 127.0.0.1
@@ Line 523: / Line 523: @@
 ===== Thread deadlock =====
-{{ :at-m42:deadlock1.png?768 |Deadlock}}
+{{:at-m42:deadlock1.png?768 |Deadlock}}
-Thread deadlock scenario
-Thread A enters synchronized method of object foo and gets the key.
-Thread A goes to sleep
-Thread deadlock scenario
-Thread B enters synchronized method of object bar and gets the key.
-Thread B tries to enter a synchronized method of object foo, but can't get that key (A has it).
-B "blocks" waiting for foo's key to become available.
-B keeps the bar key.
-Thread deadlock scenario
-Thread A wakes up and tries to enter a synchronized method on object bar., but can't get that key because B has it.
-A "blocks" waiting for bar's key to become available.
-Thread A can't run until it get's bar key that B is holding.
-Thread B can't run until it gets the foo key that A is holding.
-Deadlock!
-Summary
-Single-threaded programming: live by yourself, own everything, no contention for resources
-Multithreading: suddenly you can have collisions and destroy information, get locked up over the use of resources
-Multithreading makes Java complicated, but that’s not Java’s fault. Multithreading is hard
-Lab Exercises
-.	Inherit a class from Thread and override the run( ) method. Inside run( ), print a message, then call sleep( ). Repeat this 3 times, then return from run( ). Put a start-up message in the constructor and override finalize( ) to print a shut-down message. Make a separate thread class that calls System.gc( ) inside run( ), printing a message as it does so. Make several thread objects of both types and run them to see what happens.
-.	Create two Thread classes, one with a run( ) that starts up, creates and passes its own handle to an object of the second thread class and then calls wait( ). The other classes’ run( ) should cause a notifyAll( ) in the first thread after some number of seconds have passed, so the first thread can print out a message.
-{{:at-m42:deposit.png|}}
+===== Thread deadlock scenario =====
-{{:at-m42:deadlock1.png|}}
-===== Heading 1 =====
+{{:at-m42:deadlock2.png?344 | Deadlock 2.}}
-<code groovy 1 | Example 1: Everything is an object (at-m42/Examples/lecture02/example1.groovy)>
+  * ''Thread'' A enters ''synchronized'' method of object ''foo'' and gets the key.
-extern> http://www.cpjobling.org.uk/~eechris/at-m42/Examples/lecture02/example1.groovy
+  * ''Thread'' A goes to sleep
-</code>
-----
-Notes ...
+===== Thread deadlock scenario =====
-===== Heading 2 =====
+{{:at-m42:deadlock3.png?455 |}}
-  * [[#Sub head 1]]
+  * ''Thread'' B enters ''synchronized'' method of object ''bar'' and gets the key.
-  * [[#Sub head 2]]
+  * ''Thread'' B tries to enter a ''synchronized'' method of object ''foo'', but can't get that key (A has it).
+  * B "blocks" waiting for ''foo'''s key to become available.
+  * B keeps the ''bar'' key.
+===== Thread deadlock scenario =====
+{{:at-m42:deadlock4.png?455 |Deadlock1}}
+  * ''Thread'' A wakes up and tries to enter a ''synchronized'' method on object ''bar'', but can't get **that** key because B has it.
+  * A "blocks" waiting for ''bar'''s key to become available.
+  * ''Thread'' A can't run until it gets ''bar'' key that B is holding.
+  * Thread B can't run until it gets the ''foo'' key that A is holding.
+  * **Deadlock!**
-===== Summary of this Lecture ====
+===== Summary =====
+  * Single-threaded programming: live by yourself, own everything, no contention for resources
-The ....
+  * Multi-threading: suddenly you can have collisions and destroy information, get locked up over the use of resources
+  * Multi-threading makes programming on the Java Platform complicated.
+  * Groovy multithreading easier because of the use of the closure.
-  * [[#Heading 1]]
+  * **Multi-threading is hard**!
-  * [[#Heading 2]]
-  * [[#heading 3]]
-===== Lab Exercises =====
-  * [[eg-m42:labs:lab1|Lab 1]] exercises 1-7.
 ----