Package org.apfloat

Class ApfloatContext

java.lang.Object
org.apfloat.ApfloatContext
All Implemented Interfaces:
Cloneable
public class ApfloatContext extends Object implements Cloneable
This class encapsulates the information needed by the apfloat implementation to perform computations.

All environment related settings of an apfloat implementation are accessed through an ApfloatContext. Such settings include for example the implementation provider class, maximum memory size to be used, and the file names that are used for temporary files.

For performance reasons, access to an ApfloatContext is not synchronized. Presumably, this won't be a problem in most cases. But, if the code needs to concurrently modify and access an ApfloatContext, all access to it should be externally synchronized.

At simplest, there is just one ApfloatContext, the global apfloat context. All settings in your application are retrieved through it. The global context is created when the ApfloatContext class is loaded, and it's thus always available.

Values for the different settings in the global apfloat context are specified in the apfloat.properties file, found in the class path. Since they are loaded via a ResourceBundle named "apfloat", you can alternatively deploy a ResourceBundle class named "apfloat" in your class path to avoid having a .properties file, or to define properties dynamically at run time.

The different settings that can be specified in the apfloat.properties file are as follows:

It is also possible to override the settings in apfloat.properties with system properties. They can be defined with the property names listed above, prefixed with "apfloat.".

An example apfloat.properties file could contain the following: 

 builderFactory=org.apfloat.internal.IntBuilderFactory
 defaultRadix=10
 maxMemoryBlockSize=50331648
 cacheL1Size=8192
 cacheL2Size=262144
 cacheBurst=32
 memoryThreshold=65536
 sharedMemoryTreshold=65536
 blockSize=65536
 numberOfProcessors=1
 filePath=
 fileInitialValue=0
 fileSuffix=.ap
 cleanupAtExit=true
A system property could be used to override any of the above, e.g. by setting on the command line "-Dapfloat.defaultRadix=11".

The total memory size and the number of processors are detected automatically, as reported by the Java runtime, if they are not specified in the configuration bundle.

If you need to create a complex multithreaded application that performs apfloat calculations in parallel using multiple threads, you may need to change the ApfloatContext settings for the different working threads.

If thread-specific apfloat contexts are not specified, all threads will use the global context. To set a thread specific context, you would typically create a clone() of the global (or other parent) context, and then set that context to the thread using setThreadContext(ApfloatContext,Thread). Note that if you do not create a clone of the context, the same context will still be used, since it's passed by reference.

To optimize thread usage while waiting for another thread in a multithreaded application it's recommended to use wait(Future) instead of just e.g. Future.get(). This allows threads that the library uses to perform useful work (instead of just being idle) while waiting for the Future to complete.

Typically you may need to set the following properties for each thread:

  • setNumberOfProcessors(int): Since the number of physical processors available is fixed, you may want to limit the amount of processors each thread can use. In many cases you will want each thread to use exactly one processor, and create as many threads as there are processors.
  • setMaxMemoryBlockSize(long): The physical memory is global and its amount is fixed as well. Since all threads share the global memory, you may want to limit the maximum amount of memory each thread can use. If you do this, you will probably just split the amount of memory between the threads, e.g. by dividing it equally. In this case you should set each thread to have a separate shared memory lock with setSharedMemoryLock(Object). In this solution all threads can allocate their maximum allowed memory block at the same time, and still the VM won't run out of memory.
    Another possibility is to set the whole global memory size as the maximum available for each thread, and use the same shared memory lock for every thread. This is actually the default behavior, if you don't call setMaxMemoryBlockSize(long) nor setSharedMemoryLock(Object). This way all threads can access the maximum amount of physical memory available. The drawback is that the threads will synchronize on the same memory block, so only one thread can use it at a time. This can have a major effect on performance, if threads are idle, waiting to acquire the shared memory lock for most of the time. To work around this, some mechanism can be set up for pooling the threads competing for the same lock, and executing the task using parallel threads from the thread pool. For example the default apfloat multiplication algorithm uses such a mechanism. Note that synchronization against the shared memory lock will be used for all data blocks larger than the shared memory threshold (see getSharedMemoryTreshold()).
  • setFilenameGenerator(FilenameGenerator): When you clone an ApfloatContext, the filename generator is by default shared. For most situations this is fine. If you for some reason want to separate the files generated in each thread, you can just set a new FilenameGenerator for each thread. In this case it's essential to configure the FilenameGenerators not to generate conflicting file names. You can do this easily by specifying a different directory or file suffix for each filename generator, or by specifying a different starting value for the file names (e.g. 1000000, 2000000, 3000000, ...).
    Setting the filename generator may also be relevant, if you use a distributed computing platform where separate physical machines (or at least separate VM processes) create temporary files in the same shared disk storage. In this case it's also essential to configure the different processes so that they do not generate conflicting file names.

The other settings are generally global and do not typically need to be set differently for each thread.

Unfortunately, Java doesn't allow detecting automatically many of the settings, such as cache sizes. Also, for optimal performance, it would usually be desirable to set each thread's processor affinity (which physical processor runs which thread), which is also not possible. If these features are added to the Java platform in the future, they may be added to the ApfloatContext API as well.

Version:
1.9.1
Author:
Mikko Tommila

  • Field Details

    • BUILDER_FACTORY

      public static final String BUILDER_FACTORY
      Property name for specifying the apfloat builder factory class.
      See Also:

    • DEFAULT_RADIX

      public static final String DEFAULT_RADIX
      Property name for specifying the default radix.
      See Also:

    • MAX_MEMORY_BLOCK_SIZE

      public static final String MAX_MEMORY_BLOCK_SIZE
      Property name for specifying the maximum memory block size.
      See Also:

    • CACHE_L1_SIZE

      public static final String CACHE_L1_SIZE
      Property name for specifying the level 1 cache size.
      See Also:

    • CACHE_L2_SIZE

      public static final String CACHE_L2_SIZE
      Property name for specifying the level 2 cache size.
      See Also:

    • CACHE_BURST

      public static final String CACHE_BURST
      Property name for specifying the level 1 cache burst size.
      See Also:

    • MEMORY_THRESHOLD

      public static final String MEMORY_THRESHOLD
      Property name for specifying the apfloat memory threshold.
      See Also:

    • MEMORY_TRESHOLD

      @Deprecated public static final String MEMORY_TRESHOLD
      Deprecated.
      Use MEMORY_THRESHOLD.
      Property name for specifying the apfloat memory threshold.
      See Also:

    • SHARED_MEMORY_TRESHOLD

      public static final String SHARED_MEMORY_TRESHOLD
      Property name for specifying the apfloat shared memory threshold.
      See Also:

    • BLOCK_SIZE

      public static final String BLOCK_SIZE
      Property name for specifying the I/O block size.
      See Also:

    • NUMBER_OF_PROCESSORS

      public static final String NUMBER_OF_PROCESSORS
      Property name for specifying the number of processors available.
      See Also:

    • FILE_PATH

      public static final String FILE_PATH
      Property name for specifying the temporary file path.
      See Also:

    • FILE_INITIAL_VALUE

      public static final String FILE_INITIAL_VALUE
      Property name for specifying the temporary file initial value.
      See Also:

    • FILE_SUFFIX

      public static final String FILE_SUFFIX
      Property name for specifying the temporary file suffix.
      See Also:

    • CLEANUP_AT_EXIT

      public static final String CLEANUP_AT_EXIT
      Property name for specifying if clean-up should be done at program exit.
      See Also:

  • Constructor Details

  • Method Details

    • getContext

      public static ApfloatContext getContext()
      Get the ApfloatContext for the calling thread. If a thread-specific context has not been specified, the global context is returned.
      Returns:
      The ApfloatContext for the calling thread.

    • getGlobalContext

      public static ApfloatContext getGlobalContext()
      Get the global ApfloatContext.
      Returns:
      The global ApfloatContext.

    • getThreadContext

      public static ApfloatContext getThreadContext()
      Get the thread-specific ApfloatContext for the calling thread.
      Returns:
      The ApfloatContext for the calling thread, or null if one has not been specified.

    • getThreadContext

      public static ApfloatContext getThreadContext(Thread thread)
      Get the thread-specific ApfloatContext for the specified thread.
      Parameters:
      thread - The thread whose ApfloatContext is to be returned.
      Returns:
      The ApfloatContext for the specified thread, or null if one has not been specified.

    • setThreadContext

      public static void setThreadContext(ApfloatContext threadContext)
      Set the thread-specific ApfloatContext for the calling thread.
      Parameters:
      threadContext - The ApfloatContext for the calling thread.

    • setThreadContext

      public static void setThreadContext(ApfloatContext threadContext, Thread thread)
      Set the thread-specific ApfloatContext for the specified thread.
      Parameters:
      threadContext - The ApfloatContext for the specified thread.
      thread - The thread whose ApfloatContext is to be set.

    • removeThreadContext

      public static void removeThreadContext()
      Removes the thread-specific context for the current thread.

    • removeThreadContext

      public static void removeThreadContext(Thread thread)
      Removes the thread-specific context for the specified thread.
      Parameters:
      thread - The thread whose ApfloatContext is to be removed.

    • clearThreadContexts

      public static void clearThreadContexts()
      Removes all thread-specific ApfloatContexts.

    • getBuilderFactory

      public BuilderFactory getBuilderFactory()
      Get the BuilderFactory.
      Returns:
      The BuilderFactory for this ApfloatContext.

    • setBuilderFactory

      public void setBuilderFactory(BuilderFactory builderFactory)
      Set the BuilderFactory.
      Parameters:
      builderFactory - The BuilderFactory for this ApfloatContext.

    • getFilenameGenerator

      public FilenameGenerator getFilenameGenerator()
      Get the FilenameGenerator.
      Returns:
      The FilenameGenerator for this ApfloatContext.

    • setFilenameGenerator

      public void setFilenameGenerator(FilenameGenerator filenameGenerator)
      Set the FilenameGenerator.
      Parameters:
      filenameGenerator - The FilenameGenerator for this ApfloatContext.

    • getDefaultRadix

      public int getDefaultRadix()
      Get the default radix.
      Returns:
      The default radix for this ApfloatContext.

    • setDefaultRadix

      public void setDefaultRadix(int radix)
      Set the default radix. The default value is 10.
      Parameters:
      radix - The default radix for this ApfloatContext.

    • getMaxMemoryBlockSize

      public long getMaxMemoryBlockSize()
      Get the maximum memory block size.
      Returns:
      The maximum memory block size.
      See Also:

    • setMaxMemoryBlockSize

      public void setMaxMemoryBlockSize(long maxMemoryBlockSize)
      Set the maximum allowed memory block size in bytes. Apfloat will allocate an array at most of this size for calculations using this context. The minimum value for this setting is 65536.

      If you set the value of this parameter too low, performance will suffer greatly as data is unnecessarily paged to disk. If you set this value too high, your application can crash with an OutOfMemoryError.

      The default value for this setting is 80% of the total memory available to the VM at application startup, as reported by Runtime.totalMemory(), rounded down to the nearest power of two or three times a power of two.

      Parameters:
      maxMemoryBlockSize - Maximum allocated memory block size in bytes.

    • getCacheL1Size

      public int getCacheL1Size()
      Get the level 1 cache size.
      Returns:
      The level 1 cache size.
      See Also:

    • setCacheL1Size

      public void setCacheL1Size(int cacheL1Size)
      Set the L1 cache size in bytes. The minimum value for this setting is 512.

      This setting has a minor performance impact on some memory intensive operations. Unless you really want to tweak the performance, it's better to not touch this setting.

      The default value for this setting is 8kB.

      Parameters:
      cacheL1Size - The level 1 cache size in bytes.

    • getCacheL2Size

      public int getCacheL2Size()
      Get the level 2 cache size.
      Returns:
      The level 2 cache size.
      See Also:

    • setCacheL2Size

      public void setCacheL2Size(int cacheL2Size)
      Set the L2 cache size in bytes. The minimum value for this setting is 2048. This setting has a minor performance impact on some memory intensive operations. Unless you really want to tweak the performance, it's better to not touch this setting.

      The default value for this setting is 256kB.

      Parameters:
      cacheL2Size - The level 2 cache size in bytes.

    • getCacheBurst

      public int getCacheBurst()
      Get the level 1 cache burst size.
      Returns:
      The cache burst size.
      See Also:

    • setCacheBurst

      public void setCacheBurst(int cacheBurst)
      Set the L1 cache burst block size in bytes. This value is also known as "L1 cache line size".

      Some common values are:

      • 16 for 486 processors
      • 32 for Pentium MMX/II/III/Celeron series and Itanium processors
      • 64 for Pentium 4 and Itanium 2 processors
      The processor will move at least this amount of bytes whenever data is moved between the level 1 cache and other memory (lower level cache or main memory). Note that other cache levels than L1 may have a different line size. The minimum value for this setting is 8.

      This setting has a minor performance impact on some memory intensive operations. Unless you really want to tweak the performance, it's usually better to not touch this setting. Though, if you have e.g. a Pentium 4 processor, you may want to increase the value of this setting to 64 from the default value of 32.

      Parameters:
      cacheBurst - The number of bytes in a L1 cache line.

    • getMemoryTreshold

      @Deprecated public int getMemoryTreshold()
      Deprecated.
      Use getMemoryThreshold().
      Get the memory threshold.

      If the value is larger than the maximum value that can be presented in an integer, then Integer.MAX_VALUE is returned.

      Returns:
      The memory threshold.

    • setMemoryTreshold

      @Deprecated public void setMemoryTreshold(int memoryThreshold)
      Deprecated.
      Use setMemoryThreshold(long).
      Set the maximum size of apfloats in bytes that are stored in memory within this context.
      Parameters:
      memoryThreshold - The number of bytes that apfloats that are stored in memory will at most have within this context.

    • getMemoryThreshold

      public long getMemoryThreshold()
      Get the memory threshold.
      Returns:
      The memory threshold.

    • setMemoryThreshold

      public void setMemoryThreshold(long memoryThreshold)
      Set the maximum size of apfloats in bytes that are stored in memory within this context. The minimum value for this setting is 128.

      If the memory threshold is too small, performance will suffer as small numbers are stored to disk, and the amount of disk I/O overhead becomes significant. On the other hand, if the memory threshold is too big, you can get an OutOfMemoryError.

      The optimal value depends greatly on each application. Obviously, if you have plenty of heap space and don't create too many too big numbers you are not likely to have problems. The default value of this setting is 64kB, or the maximum heap size divided by 1024, whichever is larger.

      Parameters:
      memoryThreshold - The number of bytes that apfloats that are stored in memory will at most have within this context.

    • getSharedMemoryTreshold

      public long getSharedMemoryTreshold()
      Get the shared memory threshold.
      Returns:
      The shared memory threshold.
      See Also:

    • setSharedMemoryTreshold

      public void setSharedMemoryTreshold(long sharedMemoryTreshold)
      Set the maximum size of apfloats in bytes that can be used without synchronizing against the shared memory lock. The minimum value for this setting is 128.

      If only one thread is used then this setting has no effect. If multiple threads are used, and this setting is too small, performance will suffer as the synchronization blocking and other overhead becomes significant. On the other hand, if the numbers are being stored in memory, and the shared memory threshold is too big, you can get an OutOfMemoryError.

      The optimal value depends on the application and the way parallelism is used. As a rule of thumb, this should be set to a value that is the maximum memory block size divided by the number of parallel threads. The default is somewhat more conservatively this number divided by 32.

      Parameters:
      sharedMemoryTreshold - The number of bytes that apfloats will at most have, without synchronizing against the shared memory lock, within this context.

    • getBlockSize

      public int getBlockSize()
      Get the I/O block size.
      Returns:
      The I/O block size.
      See Also:

    • setBlockSize

      public void setBlockSize(int blockSize)
      Set the efficient I/O block size in bytes for this context. The minimum value for this setting is 128.

      If the block size is too small, the overhead of each I/O call will definetely have an adverse effect on performance. Setting the block size very big will not affect performance significantly, but can increase intermediate memory consumption a lot, possibly resulting in running out of memory with an OutOfMemoryError. A recommended minimum value is at least a few kilobytes.

      In many places, data in files is accessed in reverse order, fetching blocks of this size. Probably the optimal value of this setting is roughly half of the read-ahead buffer size of you hard disk. The default value is 64kB.

      Parameters:
      blockSize - The I/O block size in bytes to be used in calculations using this context.

    • getNumberOfProcessors

      public int getNumberOfProcessors()
      Get the number of processors that should be used for parallel calculations.
      Returns:
      The number of processors.
      See Also:

    • setNumberOfProcessors

      public void setNumberOfProcessors(int numberOfProcessors)
      Set the number of processors available to parallel calculations using this context. The minimum value for this setting is 1. The default is to use all processors (CPU cores) available.

      Note that if you change the number of processors after the library has been initialized, the number of threads available to the ExecutorService is not changed. If you want to change that too, it can be done easily with setExecutorService(ApfloatContext.getDefaultExecutorService()).

      Parameters:
      numberOfProcessors - Number of processors available to parallel calculations using this context.
      See Also:

    • getCleanupAtExit

      public boolean getCleanupAtExit()
      Get if clean-up should be performed at the time the program exits.
      Returns:
      true if clean-up will be done at JVM exit, or false if not.
      See Also:

    • setCleanupAtExit

      public void setCleanupAtExit(boolean cleanupAtExit)
      Set if clean-up should be performed at the time the program exits. The clean-up runs garbage collection and finalization to remove any remaining temporary files that may have been created. The default behavior is true.

      For example unsigned applets must have this property set to false, since they do not have access to setting shutdown hooks.

      Note that if this setting is ever set to true in any ApfloatContext (and never set to false subsequently in that context), then clean-up will be performed.

      Also note that having the shutdown hook set will prevent class garbage collection i.e. the apfloat classes can't be unloaded if the shutdown hook still references the ApfloatContext class. If class unloading is desired then the cleanupAtExit property should be set to false first.

      Parameters:
      cleanupAtExit - true if clean-up should be done at JVM exit, or false if not.

    • getProperty

      public String getProperty(String propertyName)
      Get the value of a property as string. The name of the property can be any of the constants defined above.
      Parameters:
      propertyName - The name of the property.
      Returns:
      The value of the property as a String.

    • getProperty

      public String getProperty(String propertyName, String defaultValue)
      Get the value of a property as string, with the provided default value if the property is not set.
      Parameters:
      propertyName - The name of the property.
      defaultValue - The default value to be returned, if the property is not set.
      Returns:
      The value of the property as a String.
      Since:
      1.7.0

    • setProperty

      public void setProperty(String propertyName, String propertyValue) throws ApfloatConfigurationException
      Set the value of a property as string. The name of the property can be any of the constants defined above.
      Parameters:
      propertyName - The name of the property.
      propertyValue - The value of the property as a String.
      Throws:
      ApfloatConfigurationException - If the property value can't be converted to the correct type.

    • getProperties

      public Properties getProperties()
      Get the values of all properties as strings. The names of the properties are all of the constants defined above.
      Returns:
      The properties.

    • getSharedMemoryLock

      public Object getSharedMemoryLock()
      Get the shared memory lock object. All internal functions that allocate a memory block larger than the shared memory threshold should synchronize the allocation and memory access on the object returned by this method.
      Returns:
      The object on which large memory block allocation and access should be synchronized.

    • setSharedMemoryLock

      public void setSharedMemoryLock(Object lock)
      Set the shared memory lock object. All internal functions that allocate a memory block larger than the shared memory threshold should synchronize the allocation and memory access on the object passed to this method.

      The object is not used for anything else than synchronization, so the class of the object should really be java.lang.Object. One would typically call this method e.g. as ctx.setSharedMemoryLock(new Object()).

      Parameters:
      lock - The object on which large memory block allocation and access should be synchronized.

    • getExecutorService

      public ExecutorService getExecutorService()
      Get the ExecutorService. It can be used for executing operations in parallel.

      By default the ExecutorService is a thread pool that is shared by all the ApfloatContexts. The threads in the pool are daemon threads so the thread pool requires no clean-up at shutdown time.

      Returns:
      The ExecutorService.
      Since:
      1.1
      See Also:

    • setExecutorService

      public void setExecutorService(ExecutorService executorService)
      Set the ExecutorService.

      If a custom ExecutorService is used, e.g. a thread pool, then the number of available threads in the pool should match the number of processors set to all ApfloatContexts with setNumberOfProcessors(int).

      Note that if a custom ExecutorService that requires shutdown is used, it is the caller's responsibility to clean up the ExecutorService at shutdown.

      Parameters:
      executorService - The ExecutorService.
      Since:
      1.1
      See Also:

    • wait

      public void wait(Future<?> future)
      While waiting for a Future to be completed, do some useful work instead of just being idle.

      This method is intended to coordinate with the executor service from getExecutorService() to keep all threads busy at all times.

      Parameters:
      future - The Future to wait for.
      Since:
      1.9.0

    • getAttribute

      public Object getAttribute(String name)
      Get an arbitrary object as an attribute for this ApfloatContext.
      Parameters:
      name - Name of the attribute.
      Returns:
      Value of the attribute or null if the attribute doesn't exist.

    • setAttribute

      public Object setAttribute(String name, Object value)
      Set an arbitrary object as an attribute for this ApfloatContext.
      Parameters:
      name - Name of the attribute.
      value - Value of the attribute.
      Returns:
      Previous value of the attribute or null if the attribute didn't exist.

    • removeAttribute

      public Object removeAttribute(String name)
      Remove an attribute from this ApfloatContext.
      Parameters:
      name - Name of the attribute.
      Returns:
      Value of the attribute or null if the attribute didn't exist.

    • getAttributeNames

      public Enumeration<String> getAttributeNames()
      Get names of all attributes for this ApfloatContext.
      Returns:
      Names of all attributes as strings.

    • loadProperties

      public static Properties loadProperties() throws ApfloatRuntimeException
      Loads properties from a properties file or resource bundle. First the ResourceBundle by the name "apfloat" is located, then all properties found from that resource bundle are put to a Properties object.

      The resource bundle is found basically using the following logic (note that this is standard Java ResourceBundle functionality), in this order whichever is found first:

      1. From the class named apfloat (that should be a subclass of ResourceBundle), in the current class path
      2. From the file "apfloat.properties" in the current class path
      Returns:
      Properties found in the "apfloat" resource bundle, or an empty Properties object, if the resource bundle is not found.
      Throws:
      ApfloatRuntimeException

    • getDefaultExecutorService

      public static ExecutorService getDefaultExecutorService()
      Returns a new instance of a default ExecutorService.

      The default executor service is a ForkJoinPool where the number of threads is one less than the number of processors set with setNumberOfProcessors(int).

      Returns:
      A new instance of a default ExecutorService.
      Since:
      1.3

    • setProperties

      public void setProperties(Properties properties) throws ApfloatConfigurationException
      Set the values of all properties as strings. The names of the properties can be all of the constants defined above.
      Parameters:
      properties - The properties.
      Throws:
      ApfloatConfigurationException - If a property value can't be converted to the correct type.

    • clone

      public Object clone()
      Creates a copy of this object.

      The clone has the same BuilderFactory and FilenameGenerator members and the same shared memory lock and ExecutorService as the original ApfloatContext.

      A shallow copy of the property set and the attribute set is created. Thus setting a property or attribute on the clone will not set it in the original object. Since the actual attributes (values) are shared, if an attribute is mutable and is modified in the clone, the modified value will appear in the original also.

      Overrides:
      clone in class Object
      Returns:
      A mostly shallow copy of this object.