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Common Problems in Java SE Application

This message is based on the following materials.

http://java.sun.com/developer/technicalArticles/J2SE/monitoring/#Insufficient_Memory

http://java.sun.com/developer/technicalArticles/javase/troubleshoot//

1. Java Memory Basic

1.1 Heap, Non-Heap, and Native

Heap memory is the runtime data area from which memory for all class instances and arrays is allocated.
Non-heap memory includes the method area and memory required for the internal processing or optimization of the JVM.
It stores per-class structures such as a runtime constant pool, field
and method data, and the code for methods and constructors.
Native memory is the virtual memory
managed by the operating system. When the memory is insufficient for an
application to allocate, a java.lang.OutOfMemoryError will be thrown.

1.2 GC and Full GC

The garbage collector (GC) detects garbage, defined as objects that are
no longer reachable, then reclaims it and makes space available to the
running program. The GC typically works in a stop-the-world fashion --
that is, it freezes the heap when working.

The above diagram describes the layout of HotSpot VM Heap and it
consists of three parts: perm generation, old generation and new/yang
generation. The perm generation is basically for class loading. Next
are the old and young generation. The young generation is further
broken up into three spaces: Eden, Survivor Space 1 (SS#1) and Survivor
Space 2 (SS#2).

2. Memory Problems: out of memory, memory leak and Frequently full GC

• java.lang.OutOfMemoryError: Java heap space => It indicates that an object could not be allocated in the Java heap.
  1. Configuration issue, where the specified heap size (or the default
     size, if not specified) is insufficient for the application.
  2. The application is unintentionally holding references to objects, and
     this prevents the objects from being garbage collected. This is the
     Java language equivalent of a memory leak.
  3. One other potential source of OutOfMemoryError arises with applications that make excessive use of finalizers.
• java.lang.OutOfMemoryError: PermGen space => the permanent generation is full.
  1. If
     an application loads a very large number of classes, then the size of
     the permanent generation might need to be increased using the
     -XX:MaxPermSize option.
  2. Interned java.lang.String
     objects are also stored in the permanent generation.If an application
     interns a huge number of strings, the permanent generation might need
     to be increased from its default setting.
• java.lang.OutOfMemoryError: Requested array size exceeds VM limit
        attempted to allocate an array that is larger than the heap size
• java.lang.OutOfMemoryError: request <size> bytes for <reason>. Out of swap space?
      
  The Java Native Interface (JNI) code or the native library of an
  application and the JVM implementation allocate memory from the native
  heap. An OutOfMemoryError will be thrown when an allocation in the
  native heap fails.
• java.lang.OutOfMemoryError: <reason> <stack trace> (Native method)
      
  an indication that a native method has encountered an allocation
  failure. The difference between this and the previous message is that
  the allocation failure was detected in a JNI or native method rather
  than in Java VM code.
  
  

3. Thread Problems: dead lock, infinite loop and high lock contention

• Dead Lock
  
  1. block
     by object monitor: Each object is associated with a monitor. If a
     thread invokes a synchronized method on an object, that object is
     locked.
  2. block by java.util.concurrent.locks
• Looping Thread
       If
  thread CPU time is continuously increasing, but it is not unresponsive.
  An infinite loop may consume all available CPU cycles and cause the
  rest of the application to be unresponsive.
• High Lock Contention
      
  Synchronization is heavily used in multithreaded applications to ensure
  mutually exclusive access to a shared resource or to coordinate and
  complete tasks among multiple threads.
  Or too many threads are waiting for a limited resource.

Troubleshooting Tools in Java SE Application

1. Command line tools

2. Visual Tools