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How to run custom clean-up code to prevent JVM from throwing OutOfMemory? [duplicate]

I will be running a genetic algorithm on my roommate's computer for the whole weekend, and I'm afraid that it could run out of memory over such a long run. However, my algorithm works in such a way that would make it reasonably easy to trim less useful results, so if there was a way to tell when my program is about to run out of heap space, I could probably make room and keep going for some more time.
Is there a way to be notified when the JVM is running out of heap space, before the OutOfMemoryError?

You can register a javax.management.NotificationListener that is called when a certain threshold is hit.
Something like
final MemoryMXBean memBean = ManagementFactory.getMemoryMXBean();
final NotificationEmitter ne = (NotificationEmitter) memBean;
ne.addNotificationListener(listener, null, null);
final List<MemoryPoolMXBean> memPools = ManagementFactory
.getMemoryPoolMXBeans();
for (final MemoryPoolMXBean mp : memPools) {
if (mp.isUsageThresholdSupported()) {
final MemoryUsage mu = mp.getUsage();
final long max = mu.getMax();
final long alert = (max * threshold) / 100;
mp.setUsageThreshold(alert);
}
}
Where listener is your own implementation of NotificationListener.

You can try this:
// Get current size of heap in bytes
long heapSize = Runtime.getRuntime().totalMemory();
// Get maximum size of heap in bytes. The heap cannot grow beyond this size.
// Any attempt will result in an OutOfMemoryException.
long heapMaxSize = Runtime.getRuntime().maxMemory();
// Get amount of free memory within the heap in bytes. This size will increase
// after garbage collection and decrease as new objects are created.
long heapFreeSize = Runtime.getRuntime().freeMemory();
As found here - http://www.exampledepot.com/egs/java.lang/GetHeapSize.html

Just use WeakReferences for the discardable results, then they will be discarded if necessary for space reasons.

I am not sure about this, but can't JConsole solve your purpose ??

How to get total JVM heap size, used memory using Java

pro-grammatically how to get total Heap size, used heap memory ?

You can use Runtime class methods
maxMemory() , freeMemory() and totalMemory()
and if you want to use any tools then there are so many tools like jProfiler.

You can use MemoryMXBean to get info about your heap
MemoryMXBean mbean = ManagementFactory.getMemoryMXBean();
System.out.println(mbean.getHeapMemoryUsage());
which outputs
init = 134217728(131072K) used = 2044912(1996K)
committed = 128974848(125952K) max = 1897922560(1853440K)

Finding how much virtual memory is allocated to a process

Is there a way to find out how much total virtual memory is allocated to a specific process? I have a program and I am also putting in a performance tracker which will monitor how much memory the process is using and how much is left for it to use.
To do this, I need to know how much memory is allocated to the process. Is there a way to do this in Java? I am running on Windows 7.
Also, I have currently been using the Sigar classes to monitor other memory statistics. Does sigar have a specific class/function that can find what I am looking for?

You can use Visualvm.
In your code to calculate memory used:-
Runtime runtime = Runtime.getRuntime(); // Get the Java runtime
long memory = runtime.totalMemory() - runtime.freeMemory(); // Calculate the used memory

To add more on what #Mitesh mentioned,
int var=1; // for bytes. you can change here to print in MB or KB as you wish
log.info("************************* PRINTING MEMORY USAGE - BEGIN **************");
Runtime runtime = Runtime.getRuntime();
/* Total number of processors or cores available to the JVM */
log.info("Available processors (cores): "
+ runtime.availableProcessors());
/* This will return Long.MAX_VALUE if there is no preset limit */
long maxMemory = runtime.maxMemory();
/* Maximum amount of memory the JVM will attempt to use */
log.info("Maximum memory : "
+ (maxMemory == Long.MAX_VALUE ? "no limit" : maxMemory / var));
/* Total memory currently available to the JVM */
long totalMemory = runtime.totalMemory() / var;
log.info("Total memory available to JVM : "
+ totalMemory);
/* Total amount of free memory available to the JVM */
long freeMemory = runtime.freeMemory() / var;
log.info("Free memory : " + freeMemory);
// Calculate the used memory
long usedMemory = totalMemory - freeMemory;
log.info("Used memory : " + usedMemory);

Can a Java program detect that it's running low on heap space?

I will be running a genetic algorithm on my roommate's computer for the whole weekend, and I'm afraid that it could run out of memory over such a long run. However, my algorithm works in such a way that would make it reasonably easy to trim less useful results, so if there was a way to tell when my program is about to run out of heap space, I could probably make room and keep going for some more time.
Is there a way to be notified when the JVM is running out of heap space, before the OutOfMemoryError?

You can register a javax.management.NotificationListener that is called when a certain threshold is hit.
Something like
final MemoryMXBean memBean = ManagementFactory.getMemoryMXBean();
final NotificationEmitter ne = (NotificationEmitter) memBean;
ne.addNotificationListener(listener, null, null);
final List<MemoryPoolMXBean> memPools = ManagementFactory
.getMemoryPoolMXBeans();
for (final MemoryPoolMXBean mp : memPools) {
if (mp.isUsageThresholdSupported()) {
final MemoryUsage mu = mp.getUsage();
final long max = mu.getMax();
final long alert = (max * threshold) / 100;
mp.setUsageThreshold(alert);
}
}
Where listener is your own implementation of NotificationListener.

You can try this:
// Get current size of heap in bytes
long heapSize = Runtime.getRuntime().totalMemory();
// Get maximum size of heap in bytes. The heap cannot grow beyond this size.
// Any attempt will result in an OutOfMemoryException.
long heapMaxSize = Runtime.getRuntime().maxMemory();
// Get amount of free memory within the heap in bytes. This size will increase
// after garbage collection and decrease as new objects are created.
long heapFreeSize = Runtime.getRuntime().freeMemory();
As found here - http://www.exampledepot.com/egs/java.lang/GetHeapSize.html

Just use WeakReferences for the discardable results, then they will be discarded if necessary for space reasons.

I am not sure about this, but can't JConsole solve your purpose ??

Java on Linux - RES vs totalMemory()

I have a Java application running on Linux with Xmx set to 1200M
When I check the process in TOP, I see numbers like:
VIRT = 1412m
RES = 237m
SHR = 58m
Inside the Java application, I am printing the Runtime.getRuntime().totalMemory() every minute and the number there shows:
totalMemory() = 108M
Why such a big difference between the values of RES and totalMemory()?
My understanding (which could be wrong) -- totalMemory() is the memory used right now in the Heap. RES -- actual RAM memory used by the Process.
As an update:
Yes, I would expect the RES > totalMemory() - but the difference here is 237MB - 108MB = 129MB. So if someone asks me, what is the maximum memory that my Java application can use, it should be 1200MB + "something" - question is how to know that "something" .. is it 150MB? 200MB? 300MB?

RES will probably include the size of the shared libraries loaded by the JVM, many of which might also be loaded for other applications (such as the C runtime library) and as such don't really count against the actual memory usage of the JVM, but are considered part of its resident memory image.
Actual interpretation of the results of ps or top are probably better directed to superuser.org or serverfault.org.

totalMemory just is a Max heap size, the Java process contains Java heap and otherthings,for example,permanent area,so the size of RES always is biger than java heap's.