mondrian.util

Interface MemoryMonitor.Listener

Enclosing interface:

MemoryMonitor

public static interface MemoryMonitor.Listener

A MemoryMonitor client implements the Listener interface and registers with the MemoryMonitor. When the MemoryMonitor detects that free memory is low, it notifies the client by calling the client's memoryUsageNotification method. It is important that the client quickly return from this call, that the memoryUsageNotification method does not do a lot of work. It is best if it simply sets a flag. The flag should be polled by an application thread and when it detects that the flag was set, it should take immediate memory relinquishing operations. In the case of Mondrian, the present query is aborted.

Method Summary

Modifier and Type	Method and Description
void	memoryUsageNotification(long usedMemory, long maxMemory) When the MemoryMonitor determines that the Listener's threshold is equal to or less than the current available memory (post garbage collection), then this method is called with the current memory usage, usedMemory, and the maximum memory (which is a constant per JVM invocation).

Method Detail

memoryUsageNotification

void memoryUsageNotification(long usedMemory,
                             long maxMemory)

When the MemoryMonitor determines that the Listener's threshold is equal to or less than the current available memory (post garbage collection), then this method is called with the current memory usage, usedMemory, and the maximum memory (which is a constant per JVM invocation).

This method is called (in the case of Java5) by a system thread associated with the garbage collection activity. When this method is called, the client should quickly do what it needs to to communicate with an application thread and then return. Generally, quickly de-referencing some big objects and setting a flag is the most that should be done by implementations of this method. If the implementor chooses to de-reference some objects, then the application code must be written so that if will not throw a NullPointerException when such de-referenced objects are accessed. If a flag is set, then the application must be written to check the flag periodically.

Parameters:

usedMemory - the current memory used.

maxMemory - the maximum available memory.