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-- Copyright 2005 by
Kindly hosted at: |
2005/5/10
Heaps
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| Heaps | Allocator | Memory Debuging | RC/GC mechanism | ACDK contains a flexible Memory Management Framework
Stack object are fast, easy to manage, thread and exception safe. |
Stack / HeapObjects
Stack
acdk::lang::System
jlong mmu = System::getMaxMemoryUsage();
jlong cmu = ObjectHeap::curMemUsage();
System::setMaxMemoryUsage(cmu + 1024 * 1024 * 2);
for (int i = 0; i < 1000; ++i)
{
// in the background automatically Mark/Sweek GC will be called
RGcableObject lobj = new GcableObject();
lobj->_other = lobj; // cyclic reference, reference counting gc will not work
}
System::setMaxMemoryUsage(mmu);
System::gc(); // clean garbage
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Sample for handling out of memory situation
jlong mmu = System::getMaxMemoryUsage();
jlong cmu = ObjectHeap::curMemUsage();
System::setMaxMemoryUsage(cmu + 1024 * 1024 * 2);
try {
RObjectArray holder = new ObjectArray(0);
// run until out of mem
while (true)
{
holder->append(new String("Just a Text"));
}
} catch (ROutOfMemoryException ex) {
}
System::setMaxMemoryUsage(mmu);
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Iterates all heap objects
Following source demonstrates how listing all root objects work:
RInteger rint1 = new Integer(12345678); // is root object
RInteger rint2 = new Integer(8765432);
RObjectArray n = new ObjectArray(1);
n[0] = &rint2; // rint2 is not root, because member of n
// get all root objects
RObjectArray roots = System::getRootObjects();
testAssert(roots->find(&rint1) != -1);
testAssert(roots->find(&rint2) == -1);
for (int i = 0; i < roots->length(); ++i)
{
RObject o = roots[i];
if (instanceof(o, ObjectArray) == true)
{
RObjectArray oa = (RObjectArray)o;
::acdk::lang::System::out->println(
SBSTR("Root Object: (" << Integer::toHexString((int)(void*)o.impl()) << "): "
<< o->getClass()->getName() << ": " << oa->length()));
for (int i = 0; i < oa->length(); ++i)
{
o = oa[i];
if (o != Nil)
::acdk::lang::System::out->println(
SBSTR(" RootArray Object: (" << Integer::toHexString((int)(void*)o.impl()) << "): "
<< o->getClass()->getName() << ": " << o->toString()));
}
}
else
{
::acdk::lang::System::out->println(
SBSTR("Root Object: (" << Integer::toHexString((int)(void*)o.impl()) << "): "
<< o->getClass()->getName() << ": " << o->toString()));
}
}
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Additionally features
If an memory object will be freed in the PageAllocator Heap, the heap checks if
somebody wrote outside the bounds of the memory object. RC_Heap
A simple Reference Counting Heap.It doesn't support Mark/Sweep garbage collecting for cyclic objects.
The memory will be allocated directly from the underlying C/C++ heap.
RC_GC_Heap
A Heap based on Reference Counting + Garbage Collecting
for cyclic references.The memory will be allocated directly from the underlying C/C++ heap.
The bookkeeping will of all allocated memory chunks will be done container.
GC_Heap
Garbage Collecting Heap using the Boehm Garbage Collector. Install the Boehm Garbage Collector
Unfortunatelly the Boehm GC doens't work with ACDK in a stable way.I will spend for this a little more time.
To integrate the Boehm Garbage Collector you have to do following steps:
- Download the Boehm Garbage Collector 6.0 or later.
- add the library gc.lib to all ACDK libraries and executable.
- add gc6.0/include path to your Include Path.
- Add the defines to ACDK_HAS_BOEHMGC and ACDK_NO_REFCOUNTING to your
ACDK projects. Alternativally you can edit the ./acdk/Config.h file
and add these defines.
- Copy the gc.dll/gc.so to the ACDKHOME/bin directory.
Usage
Other changes in the ACDK sources are not necessary.
But there are some limitations:- The BGC will not work with other Heaps, because for performance
reasons the Reference Counting will be deactivated when using the BGC.
- Some special Debugging features inspecting the allocated Objects
will not work.
- The WeakReference/WeakHashmap will not work.
- Currently no destructor will work.