Non-Allocating Methods
Draft 1 for Discussion
Peter Dibble
September 2004
RTSJ threads executing out of heap context need to use library classes cautiously. Any objects allocated by methods in these classes will come from the current allocation context. This is not necessarily a ?bad thing,? but unexpected object allocation is a memory leak and can lead to out of memory errors.
In many cases you can tell that a method does no object allocation by inspection. If a method does not contain the new operator, does not concatenate strings, and does not invoke any other methods, it is a non-allocating method. If it invokes other methods, the only practical approaches are to assume it is an allocating method or write a tool[1] to traverse all possible call trees for that method.
Since Java is a dynamic language, the tool has to see all the classes that will be in the execution environment, but as an experiment I assumed that the J2SE 1.4.2 classes.jar is the entire execution environment. This class library includes 66945 non-abstract public or protected methods of which 27295 don?t allocate objects and either invoke no methods or only invoke other methods that cannot allocate.
The following table summarizes the results of this analysis broken down by the main Java packages.
|
Package |
Non-Allocating Count |
Allocating Count |
Package |
Non-Allocating Count |
Allocating Count |
|
com.sun.accessibility |
11 |
0 |
com.sun.corba |
1357 |
2630 |
|
com.sun.image |
31 |
42 |
com.sun.imageio |
65 |
155 |
|
com.sun.java |
768 |
2309 |
com.sun.javadoc |
28 |
102 |
|
com.sun.jdi |
181 |
212 |
com.sun.jndi |
183 |
839 |
|
com.sun.media |
277 |
295 |
com.sun.naming |
4 |
20 |
|
com.sun.org |
45 |
177 |
com.sun.rmi |
8 |
8 |
|
com.sun.security |
46 |
92 |
com.sun.swing |
20 |
0 |
|
com.sun.tools |
1171 |
3611 |
java.applet. |
21 |
24 |
|
java.awt. |
827 |
1191 |
java.awt.color |
9 |
35 |
|
java.awt.datatransfer |
20 |
76 |
java.awt.dnd |
85 |
118 |
|
java.awt.event |
96 |
57 |
java.awt.font |
109 |
120 |
|
java.awt.geom |
324 |
201 |
java.awt.im |
35 |
13 |
|
java.awt.image |
293 |
447 |
java.awt.peer |
144 |
0 |
|
java.awt.print |
33 |
26 |
java.beans. |
133 |
125 |
|
java.beans.beancontext |
44 |
109 |
java.beans. |
2 |
24 |
|
java.io. |
200 |
499 |
java.lang. |
319 |
341 |
|
java.lang.ref |
9 |
5 |
java.lang.reflect |
63 |
41 |
|
java.math. |
17 |
57 |
java.net. |
218 |
295 |
|
java.nio. |
325 |
821 |
java.nio.channels |
101 |
58 |
|
java.nio.charset |
51 |
40 |
java.rmi. |
3 |
10 |
|
java.rmi.activation |
20 |
40 |
java.rmi.dgc |
5 |