Source for java.lang.management.MemoryMXBean

   1: /* MemoryMXBean.java - Interface for a memory bean
   2:    Copyright (C) 2006 Free Software Foundation
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
  10: 
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version. */
  37: 
  38: package java.lang.management;
  39: 
  40: /**
  41:  * <p>
  42:  * Provides access to information about the memory used
  43:  * by the virtual machine.  An instance of this bean is
  44:  * obtained by calling
  45:  * {@link ManagementFactory#getMemoryMXBean()}.
  46:  * </p>
  47:  * <p>
  48:  * The Java virtual machine uses two types of memory:
  49:  * heap memory and non-heap memory.  The heap is the
  50:  * storage location for class and array instances, and is
  51:  * thus the main source of memory associated with running
  52:  * Java programs.  The heap is created when the virtual
  53:  * machine is started, and is periodically scanned by the
  54:  * garbage collector(s), in order to reclaim memory which
  55:  * is no longer used (e.g. because an object reference has
  56:  * gone out of scope).
  57:  * </p>
  58:  * <p>
  59:  * Non-heap memory is used by the virtual machine in order to
  60:  * perform its duties.  Thus, it mainly acts as the storage
  61:  * location for structures created as a result of parsing Java
  62:  * bytecode, such as the constant pool and constructor/method
  63:  * declarations.  When a Just-In-Time (JIT) compiler is in
  64:  * operation, this will use non-heap memory to store compiled
  65:  * bytecode.
  66:  * </p>
  67:  * <p>
  68:  * Both types of memory may be non-contiguous.  During the
  69:  * lifetime of the virtual machine, the size of both may
  70:  * either change (either expanding or contracting) or stay
  71:  * the same.
  72:  * </p>
  73:  * <h2>Notifications</h2>
  74:  * <p>
  75:  * Implementations of this interface also conform to the
  76:  * {@link javax.management.NotificationEmitter} interface,
  77:  * and supply two notifications reflecting memory usage.
  78:  * These notifications occur when a usage threshold is
  79:  * exceeded; for more details of these, see the documentation
  80:  * of {@link MemoryPoolMXBean}.  If threshold monitoring
  81:  * is supported, then a notification will be emitted each time
  82:  * the threshold is crossed.  Another notification will not
  83:  * be emitted unless the usage level has dropped below the
  84:  * threshold again in the meantime.
  85:  * </p>
  86:  * <p>
  87:  * The emitted notifications are instances of
  88:  * {@link javax.management.Notification}, with a type of
  89:  * either
  90:  * {@link java.lang.management.MemoryNotificationInfo#MEMORY_THRESHOLD_EXCEEDED}
  91:  * or
  92:  * {@link java.lang.management.MemoryNotificationInfo#MEMORY_COLLECTION_THRESHOLD_EXCEEDED}
  93:  * (depending on whether the notification refers to the general
  94:  * usage threshold or the garbage collection threshold) and an instance
  95:  * of {@link java.lang.management.MemoryNotificationInfo} contained
  96:  * in the user data section.  This is wrapped inside an instance
  97:  * of {@link javax.management.openmbean.CompositeData}, as explained
  98:  * in the documentation for
  99:  * {@link java.lang.management.MemoryNotificationInfo}.
 100:  * </p>
 101:  *
 102:  * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
 103:  * @since 1.5
 104:  */
 105: public interface MemoryMXBean
 106: {
 107: 
 108:   /**
 109:    * Instigates a garbage collection cycle.  The virtual
 110:    * machine's garbage collector should make the best
 111:    * attempt it can at reclaiming unused memory.  This
 112:    * is equivalent to invoking {@link java.lang.System.gc()}.
 113:    *
 114:    * @see java.lang.System#gc()
 115:    */
 116:   void gc();
 117: 
 118:   /**
 119:    * Returns a {@link MemoryUsage} object representing the
 120:    * current state of the heap.  This incorporates various
 121:    * statistics on both the initial and current memory
 122:    * allocations used by the heap.
 123:    *
 124:    * @return a {@link MemoryUsage} object for the heap.
 125:    */
 126:   MemoryUsage getHeapMemoryUsage();
 127: 
 128:   /**
 129:    * Returns a {@link MemoryUsage} object representing the
 130:    * current state of non-heap memory.  This incorporates
 131:    * various statistics on both the initial and current
 132:    * memory allocations used by non-heap memory..
 133:    *
 134:    * @return a {@link MemoryUsage} object for non-heap
 135:    *         memory.
 136:    */
 137:   MemoryUsage getNonHeapMemoryUsage();
 138: 
 139:   /**
 140:    * Returns the number of objects which are waiting to
 141:    * be garbage collected (finalized).  An object is
 142:    * finalized when the garbage collector determines that
 143:    * there are no more references to that object are in
 144:    * use.
 145:    *
 146:    * @return the number of objects awaiting finalization.
 147:    */
 148:   int getObjectPendingFinalizationCount();
 149: 
 150:   /**
 151:    * Returns true if the virtual machine will emit additional
 152:    * information when memory is allocated and deallocated.  The
 153:    * format of the output is left up to the virtual machine.
 154:    *
 155:    * @return true if verbose memory output is on.
 156:    */
 157:   boolean isVerbose();
 158: 
 159:   /**
 160:    * Turns on or off the emission of additional information
 161:    * when memory is allocated and deallocated.  The format of the
 162:    * output is left up to the virtual machine.  This method
 163:    * may be called by multiple threads concurrently, but there
 164:    * is only one global setting of verbosity that is affected.
 165:    *
 166:    * @param verbose the new setting for verbose memory output.
 167:    * @throws SecurityException if a security manager exists and
 168:    *                           denies ManagementPermission("control").
 169:    */
 170:   void setVerbose(boolean verbose);
 171: 
 172: }