MemoryManager (stSoftware API)

java.lang.Object
- com.aspc.remote.memory.MemoryManager

```
public final class MemoryManager
extends java.lang.Object
```
MemoryManager handles low memory situations. Each Handler has concept of "cost" so low cost items are cleared first then medium and then high.

Examples:
- Low cost: Java Object Pooling
- Medium cost: Data loaded from the database.
- High Cost: Temporary sort tables
CacheEntry to have a accesTime element.
Change the clearMemory method of CacheTable to take a percentage
The CacheTable.get() method will set accessTime to the current time. Actually the integer version of System.currentTimeMills() when the MemoryManager's check loop last ran.
1. When the MemoryManager detects a low memory situation ( < 10%)
2. Ask ALL MemoryHandlers for an estimate of the number of elements they contain
3. Increment the cost level until at least 20% of the elements are covered.
4. For each MemoryHandler under the calculated cost level call clearMemory() with 100 percent. This clears non referenced data so many elements are not deallocated. This is done with WeakReferences
5. For each MemoryHandler at the Calculated cost level call clearMemory() with the percentage that adds up to the 20% when taking into account the elements free from the lower cost levels.
6. CacheTable is just one type of MemoryHandler. For a CacheTable if the required percentage is less than 100% we know the create time or the last cleared time and the last retrieval time. Find the mid point between these two times and clear all elements lastAccess at or before this time.
7. Call System.gc() and check the available memory is > 10% if not increment the cost level and try again
Define the system property MAX_MEMORY to set the initial threshold limit. Defaults to 32m. You may add the suffix of G, M and K.

THREAD MODE: MULTI-THREADED memory management
Since:

January 23, 1999, 2:20 PM

Author:

Nigel Leck

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`static class`	`MemoryManager.Collector` http://blog.takipi.com/garbage-collectors-serial-vs-parallel-vs-cms-vs-the-g1-and-whats-new-in-java-8/

Field Summary

Fields
Modifier and Type	Field and Description
`static MemoryManager.Collector`	`COLLECTOR`
`static java.lang.String`	`ENV_MIN_INCREMENTAL_CLEAR_TIME` the min incremental clear time environment variable
`static int`	`OVERRIDE_OCCUPANCY_FRACTION` The initiating faction set from command line.
`static java.lang.String`	`TENURED_PERCENT` The minimum TENURED percent environment variable.
`static java.lang.String`	`TENURED_SIZE` The TENURED size environment variable.

Method Summary

All Methods Static Methods Concrete Methods
Modifier and Type	Method and Description
`static void`	`addListener(MemoryListener listener)` Register a Memory listener.
`static long`	`calculatedTenuredThreshold()` the GC threshold
`static long`	`callFreeMemory(MemoryHandler handler, double percentage)` To prevent a deadlock found on 25 Oct 2003 between freeMemory() and deregister()
`static boolean`	`callGC(int intervalSeconds, java.lang.String[] logMsg)` Only call System.gc() if it has NOT been called in the last n seconds.
`static long`	`checkZone()` Are we in the safe zone ? if so clean up
`static long`	`clearMemory(MemoryHandler.Cost cost)` Clear memory ASAP Steps Clear rainy day fund to give us some space to work Call each registered memory handler with the current clear level.
`static java.util.ArrayList`	`collectStats()` Collect the stats of the memory handlers
`static void`	`deregister(MemoryHandler handler)` Removes the memory handler from the watch list.
`static long`	`estimateLevel(MemoryHandler.Cost cost)` The estimated size of the data held at this cost level
`static boolean`	`gc()` Call System.gc() regardless of when it has been called last.
`static boolean`	`gc(int intervalSeconds)` Only call System.gc() if it has NOT been called in the last n seconds.
`static long`	`getCollectionUsageThreshold()` Returns the collection usage threshold value of this memory pool in bytes.
`static long`	`getCountGC()` Number of times GC has been called.
`static java.lang.String`	`getDetails()` the memory details
`static long`	`getFreeMemory()` The free Memory, if we have defined the MAX_MEMORY to be more than what is currently reserved then add this to the free memory.
`static float`	`getFreePercent()` The percentage free.
`static long`	`getGCtime()` Total GC time.
`static MemoryHandler.Cost`	`getHighWaterMark()` The maximum level cleared.
`static long`	`getHighWaterMarkTime()` Last time the maximum level was cleared.
`static MemoryHandler.Cost`	`getLastClearedLevel()` The last level cleared
`static long`	`getLastClearedTime()` The last time memory was cleared.
`static long`	`getPanicCount()` The panic count
`static float`	`getSafeUpperPercent()` The upper safety zone as a percentage 0-1
`static int`	`getSafeZoneLower()` What is the safe zone lower currently set to ?
`static int`	`getSafeZoneUpper()` At what percentage free will we say that we are full ?
`static long`	`getTenuredFreeMemory()` The tenured free memory in bytes.
`static float`	`getTenuredFreePercent()` The tenured percentage free.
`static long`	`getTenuredTotalMemory()` get the tenured size
`static long`	`getTenuredUsed()` The amount of tenured memory used
`static int`	`getTotalClearedCount()` How many times have the memory been cleared.
`static long`	`getTotalClearedTimeTaken()` how much time has been taken clearing memory.
`static long`	`getTotalMemory()` The total memory limited to the MAX_MEMORY defined by the command line.
`static long`	`getTotalUsed()` The amount of memory used
`static boolean`	`isFull()` Is the memory full ?
`static int`	`jvmG1HeapRegionSize()` 0 - 4GB - 1MB 8GB - 2MB 16GB - 4MB 32GB - 8MB 64GB - 16MB 64GB+ - 32MB https://stackoverflow.com/questions/46786601/how-to-know-region-size-used-of-g1-garbage-collector
`static long`	`jvmMaxMemory()` Get the JVM max memory ( when will we get a out of memory error)
`static void`	`lastError()` Check if there has been an issue.
`static void`	`lastError(java.lang.String msg, java.lang.Throwable cause)` Record the an issue which has occurred by an background process.
`static long`	`lastTick()` Records the last time memory was checked (once a second or so)
`static void`	`logDetails(org.apache.commons.logging.Log logger)` Log the Memory Manager details.
`static void`	`makeRainyDay()` make sure we have ~1/2 meg to do some work
`static void`	`register(MemoryHandler handler)` Register a Memory Handler.
`static void`	`setMaxMemory(long maximum)` Manually set the maximum memory to use.
`static void`	`setMaxMemory(java.lang.String maximum)` Manually set the maximum memory to use.
`static void`	`setMinFreePercent(java.lang.String percentage)` Used to set the safe zone parameter from system properties
`static void`	`setSafeZoneLower(java.lang.String percentage)` Used to set the safe zone parameter from system properties
`static void`	`setSafeZoneUpper(java.lang.String percentage)` Used to set the safe zone parameter from system properties
`static void`	`setTenuredPercent(java.lang.String percentage)` Used to set the min tenured percentage from system properties.
`static void`	`setTenuredSize(long size)` set the tenured size
`static void`	`setTenuredSize(java.lang.String size)` Manually set the tenured size.
`static long`	`tick()` Records the last time memory was checked in seconds

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - TENURED_PERCENT
```
public static final java.lang.String TENURED_PERCENT
```
    The minimum TENURED percent environment variable. The percentage of the total memory.
    
    See Also:
    
    Constant Field Values
  - TENURED_SIZE
```
public static final java.lang.String TENURED_SIZE
```
    The TENURED size environment variable.
    
    See Also:
    
    Constant Field Values
  - COLLECTOR
```
public static final MemoryManager.Collector COLLECTOR
```
  - OVERRIDE_OCCUPANCY_FRACTION
```
public static final int OVERRIDE_OCCUPANCY_FRACTION
```
    The initiating faction set from command line.
  - ENV_MIN_INCREMENTAL_CLEAR_TIME
```
public static final java.lang.String ENV_MIN_INCREMENTAL_CLEAR_TIME
```
    the min incremental clear time environment variable
    
    See Also:
    
    Constant Field Values
- Method Detail
  - isFull
```
@CheckReturnValue
public static boolean isFull()
```
    Is the memory full ?
    
    Returns:
    
    True if with the upper limit
  - register
```
public static void register(@Nonnull
                            MemoryHandler handler)
```
    Register a Memory Handler. The Handler will be call to free up memory once a day or when low on memory
    
    Parameters:
    
    handler - The memory handler to watch.
  - addListener
```
public static void addListener(@Nonnull
                               MemoryListener listener)
```
    Register a Memory listener. The listener will be call after memory has been cleared and the low memory situation has been resolved.
    
    The listener will be held as a weak reference.
    
    Parameters:
    
    listener - The memory listener.
  - deregister
```
public static void deregister(@Nonnull
                              MemoryHandler handler)
```
    Removes the memory handler from the watch list.
    
    Parameters:
    
    handler - The memory handler to remove
  - collectStats
```
@CheckReturnValue
 @Nonnull
public static java.util.ArrayList collectStats()
                                                                    throws java.lang.InterruptedException
```
    Collect the stats of the memory handlers
    
    Returns:
    
    The memory stats
    
    Throws:
    
    java.lang.InterruptedException - the request was interrupted.
  - callFreeMemory
```
@Nonnegative
public static long callFreeMemory(@Nonnull
                                               MemoryHandler handler,
                                               @Nonnegative
                                               double percentage)
```
    To prevent a deadlock found on 25 Oct 2003 between freeMemory() and deregister()
    
    Parameters:
    
    handler - The memory handler to call
    
    percentage - The required amount to be freed
    
    Returns:
    
    The estimated number of bytes freed.
  - clearMemory
```
@Nonnegative
public static long clearMemory(@Nonnull
                                            MemoryHandler.Cost cost)
```
    Clear memory ASAP
    
    Steps
    - Clear rainy day fund to give us some space to work
    - Call each registered memory handler with the current clear level.
    Don't manually run the system.gc() as it will lock every thing up while it runs.
    Parameters:
    
    cost - Clear memory to this cost level
    
    Returns:
    
    The amount cleared
  - jvmG1HeapRegionSize
```
@CheckReturnValue
 @Nonnegative
public static int jvmG1HeapRegionSize()
```
    0 - 4GB - 1MB 8GB - 2MB 16GB - 4MB 32GB - 8MB 64GB - 16MB 64GB+ - 32MB https://stackoverflow.com/questions/46786601/how-to-know-region-size-used-of-g1-garbage-collector
    
    Returns:
    
    the estimated region size.
  - jvmMaxMemory
```
@CheckReturnValue
 @Nonnegative
public static long jvmMaxMemory()
```
    Get the JVM max memory ( when will we get a out of memory error)
    
    Returns:
    
    the "real" JVM max memory
  - setMaxMemory
```
public static void setMaxMemory(@Nonnegative
                                long maximum)
```
    Manually set the maximum memory to use.
    
    Parameters:
    
    maximum - The max memory.
  - setMaxMemory
```
public static void setMaxMemory(@Nullable
                                java.lang.String maximum)
```
    Manually set the maximum memory to use.
    
    Parameters:
    
    maximum - The max memory.
  - setSafeZoneLower
```
public static void setSafeZoneLower(@Nullable
                                    java.lang.String percentage)
```
    Used to set the safe zone parameter from system properties
    
    Parameters:
    
    percentage - The safe zone lower amount
  - setTenuredPercent
```
public static void setTenuredPercent(@Nullable
                                     java.lang.String percentage)
```
    Used to set the min tenured percentage from system properties. The tenured percentage is a percent of the max memory.
    
    Parameters:
    
    percentage - The tenured percentage
  - getSafeZoneLower
```
@CheckReturnValue
 @Nonnegative
public static int getSafeZoneLower()
```
    What is the safe zone lower currently set to ?
    
    Returns:
    
    The safe zone lower amount
  - setMinFreePercent
```
public static void setMinFreePercent(@Nullable
                                     java.lang.String percentage)
```
    Used to set the safe zone parameter from system properties
    
    Parameters:
    
    percentage - The minimum amount to free.
  - setSafeZoneUpper
```
public static void setSafeZoneUpper(@Nullable
                                    java.lang.String percentage)
```
    Used to set the safe zone parameter from system properties
    
    Parameters:
    
    percentage - The safe zone upper limit
  - getSafeZoneUpper
```
@CheckReturnValue
 @Nonnegative
public static int getSafeZoneUpper()
```
    At what percentage free will we say that we are full ?
    
    Returns:
    
    The safe zone upper limit
  - getCountGC
```
@CheckReturnValue
 @Nonnegative
public static long getCountGC()
```
    Number of times GC has been called.
    
    Returns:
    
    The number of times GC has been called.
  - getGCtime
```
@CheckReturnValue
 @Nonnegative
public static long getGCtime()
```
    Total GC time.
    
    Returns:
    
    The total time we have spent in GC
  - getTotalMemory
```
@CheckReturnValue
 @Nonnegative
public static long getTotalMemory()
```
    The total memory limited to the MAX_MEMORY defined by the command line. if MAX_MEMORY was not set and the total memory is greater than the MAX_MEMORY then set MAX_MEMORY
    
    Returns:
    
    The total number of bytes used.
  - getFreePercent
```
@CheckReturnValue
 @Nonnegative
public static float getFreePercent()
```
    The percentage free.
    
    Returns:
    
    0-1 percent free.
  - getTenuredFreeMemory
```
@CheckReturnValue
 @Nonnegative
public static long getTenuredFreeMemory()
```
    The tenured free memory in bytes.
    
    Returns:
    
    total amount of free tenured memory
  - getTenuredFreePercent
```
@CheckReturnValue
 @Nonnegative
public static float getTenuredFreePercent()
```
    The tenured percentage free.
    
    Returns:
    
    0-1 percent free.
  - getSafeUpperPercent
```
@CheckReturnValue
 @Nonnegative
public static float getSafeUpperPercent()
```
    The upper safety zone as a percentage 0-1
    
    Returns:
    
    The percentage
  - getFreeMemory
```
@CheckReturnValue
 @Nonnegative
public static long getFreeMemory()
```
    The free Memory, if we have defined the MAX_MEMORY to be more than what is currently reserved then add this to the free memory. If the reserved is more than the amount defined on the command line ignore the extra amount. For sensibility reasons never return a negative amount.
    
    Returns:
    
    the free memory
  - gc
```
public static boolean gc()
```
    Call System.gc() regardless of when it has been called last.
    
    Returns:
    
    Was it called ?
  - gc
```
public static boolean gc(@Nonnegative
                         int intervalSeconds)
```
    Only call System.gc() if it has NOT been called in the last n seconds.
    
    Parameters:
    
    intervalSeconds - Call system.gc() if not called within the last X seconds.
    
    Returns:
    
    Was it called ?
  - callGC
```
public static boolean callGC(int intervalSeconds,
                             java.lang.String[] logMsg)
```
    Only call System.gc() if it has NOT been called in the last n seconds.
    
    Parameters:
    
    intervalSeconds - Call system.gc() if not called within the last X seconds.
    
    logMsg - The message.
    
    Returns:
    
    Was it called ?
  - getTotalUsed
```
@CheckReturnValue
 @Nonnegative
public static long getTotalUsed()
```
    The amount of memory used
    
    Returns:
    
    The number of bytes used.
  - getTenuredUsed
```
@CheckReturnValue
 @Nonnegative
public static long getTenuredUsed()
```
    The amount of tenured memory used
    
    Returns:
    
    The number of bytes used.
  - lastTick
```
@CheckReturnValue
 @Nonnegative
public static long lastTick()
```
    Records the last time memory was checked (once a second or so)
    
    Returns:
    
    the last tick timestamp.
  - tick
```
@Nonnegative
public static long tick()
```
    Records the last time memory was checked in seconds
    
    Returns:
    
    the current timestamp.
  - getLastClearedLevel
```
@CheckReturnValue
 @Nonnull
public static MemoryHandler.Cost getLastClearedLevel()
```
    The last level cleared
    
    Returns:
    
    The last level cleared.
  - getTotalClearedCount
```
@CheckReturnValue
 @Nonnegative
public static int getTotalClearedCount()
```
    How many times have the memory been cleared.
    
    Returns:
    
    The number of times.
  - getTotalClearedTimeTaken
```
@CheckReturnValue
 @Nonnegative
public static long getTotalClearedTimeTaken()
```
    how much time has been taken clearing memory.
    
    Returns:
    
    The number of times.
  - getHighWaterMark
```
@CheckReturnValue
 @Nonnull
public static MemoryHandler.Cost getHighWaterMark()
```
    The maximum level cleared.
    
    Returns:
    
    The maximum level cleared.
  - getHighWaterMarkTime
```
@CheckReturnValue
 @Nonnegative
public static long getHighWaterMarkTime()
```
    Last time the maximum level was cleared.
    
    Returns:
    
    The maximum level cleared.
  - getLastClearedTime
```
@CheckReturnValue
 @Nonnegative
public static long getLastClearedTime()
```
    The last time memory was cleared.
    
    Returns:
    
    The system time last cleared.
  - lastError
```
public static void lastError()
                      throws java.lang.Exception
```
    Check if there has been an issue.
    
    Throws:
    
    java.lang.Exception - if there has been an error since the last time this method was called.
  - lastError
```
public static void lastError(java.lang.String msg,
                             java.lang.Throwable cause)
```
    Record the an issue which has occurred by an background process.
    
    Parameters:
    
    msg - the message
    
    cause - the cause.
  - estimateLevel
```
@CheckReturnValue
 @Nonnegative
public static long estimateLevel(@Nonnull
                                                                 MemoryHandler.Cost cost)
                                                          throws java.lang.InterruptedException
```
    The estimated size of the data held at this cost level
    
    Parameters:
    
    cost - The cost level
    
    Returns:
    
    The estimated amount held.
    
    Throws:
    
    java.lang.InterruptedException - the request was interrupted.
  - getDetails
```
@CheckReturnValue
 @Nonnull
public static java.lang.String getDetails()
```
    the memory details
    
    Returns:
    
    the details
  - logDetails
```
public static void logDetails(@Nonnull
                              org.apache.commons.logging.Log logger)
```
    Log the Memory Manager details.
    
    Parameters:
    
    logger - The logger to write to.
  - setTenuredSize
```
public static void setTenuredSize(@Nullable
                                  java.lang.String size)
```
    Manually set the tenured size.
    
    Parameters:
    
    size - The tenured size.
  - setTenuredSize
```
public static void setTenuredSize(long size)
```
    set the tenured size
    
    Parameters:
    
    size - the size ( negative means use the default).
  - calculatedTenuredThreshold
```
@CheckReturnValue
 @Nonnegative
public static long calculatedTenuredThreshold()
```
    the GC threshold
    
    Returns:
    
    the threshold in bytes.
  - getTenuredTotalMemory
```
@CheckReturnValue
 @Nonnegative
public static long getTenuredTotalMemory()
```
    get the tenured size
    
    Returns:
    
    the size
  - getCollectionUsageThreshold
```
@CheckReturnValue
 @Nonnegative
public static long getCollectionUsageThreshold()
```
    Returns the collection usage threshold value of this memory pool in bytes. The default value is zero.
    
    Returns:
    
    size in bytes.
  - checkZone
```
@Nonnegative
public static long checkZone()
                                   throws java.lang.InterruptedException
```
    Are we in the safe zone ? if so clean up
    
    Returns:
    
    amount of memory released.
    
    Throws:
    
    java.lang.InterruptedException - request interrupted.
  - makeRainyDay
```
@Nullable
public static void makeRainyDay()
```
    make sure we have ~1/2 meg to do some work
  - getPanicCount
```
@CheckReturnValue
 @Nonnegative
public static long getPanicCount()
```
    The panic count
    
    Returns:
    
    true if disabled

Class MemoryManager

Nested Class Summary

Field Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

TENURED_PERCENT

TENURED_SIZE

COLLECTOR

OVERRIDE_OCCUPANCY_FRACTION

ENV_MIN_INCREMENTAL_CLEAR_TIME

Method Detail

isFull

register

addListener

deregister

collectStats

callFreeMemory

clearMemory

jvmG1HeapRegionSize

jvmMaxMemory

setMaxMemory

setMaxMemory

setSafeZoneLower

setTenuredPercent

getSafeZoneLower

setMinFreePercent

setSafeZoneUpper

getSafeZoneUpper

getCountGC

getGCtime

getTotalMemory

getFreePercent

getTenuredFreeMemory

getTenuredFreePercent

getSafeUpperPercent

getFreeMemory

gc

gc

callGC

getTotalUsed

getTenuredUsed

lastTick

tick

getLastClearedLevel

getTotalClearedCount

getTotalClearedTimeTaken

getHighWaterMark

getHighWaterMarkTime

getLastClearedTime

lastError

lastError

estimateLevel

getDetails

logDetails

setTenuredSize

setTenuredSize

calculatedTenuredThreshold

getTenuredTotalMemory

getCollectionUsageThreshold

checkZone

makeRainyDay

getPanicCount