MATLAB BUILDER JA 2 User's Guide download pdf (Page 71)

Managing Native Resources

When your code accesses Java classes created by MATLAB Builder for Java,

your program uses native resources, which e xist outside the control of the

Java Virtual Machine (JVM).

Specifically, each MWArray data conversion class is a wrapper class that

encapsulates a M ATLAB m xArray. The encapsulated MATLAB array

allocates resources from the native memory heap.

Note Because the Java wrapper is small and the mxArray is relatively large,

the J VM memory manager may not call the garbage collector before the

native memory becomes exhausted or badly fragmented. This means that

native arrays should be explicitly freed.

You can use any of the following techniques to free m e mory:

• “Using Garbage Collection Provided by the JVM” on page 3-25

• “Using the dispose Method” on page 3-26

• “Overriding the O bject.Finalize Method” on page 3-27

Using Garbage Collection Provided by the JVM

When you create a new instance of a Java class, the JVM allocates and

initializes the ne w object. Wh en this object goes o u t of scope, or becomes

otherwise unreachable, it becomes eligible for garbage collection by the JVM.

The m e mory allocated by the object is eventually freed when the garbage

collector is run.

When you instantiate

MWArray classes, the encapsulated MATLAB also

allocates space for native resources, bu t these resources are not visible to the

JVM and are not eligible for garbage collection by the JVM. These resources

are not released by the class finalizer until the JVM determines that it is

appropriate to run the garbage collector.

The re sources allocated by

MWArray objects can be quite large and can quickly

exhaust your available memory. To avoid exhausting the n ative memory

3-25

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MATLAB BUILDER JA 2 User's Guide Page 71