/*
* This file is part of the Jikes RVM project (http://jikesrvm.org).
*
* This file is licensed to You under the Eclipse Public License (EPL);
* You may not use this file except in compliance with the License. You
* may obtain a copy of the License at
*
* http://www.opensource.org/licenses/eclipse-1.0.php
*
* See the COPYRIGHT.txt file distributed with this work for information
* regarding copyright ownership.
*/
package org.mmtk.utility.alloc;
import org.mmtk.plan.Plan;
import org.mmtk.policy.Space;
import org.mmtk.utility.*;
import org.mmtk.utility.statistics.*;
import org.mmtk.vm.VM;
import org.vmmagic.unboxed.*;
import org.vmmagic.pragma.*;
/**
* This abstract base class provides the basis for processor-local
* allocation. The key functionality provided is the retry mechanism
* that is necessary to correctly handle the fact that a "slow-path"
* allocation can cause a GC which violate the uninterruptability assumption.
* This results in the thread being moved to a different processor so that
* the allocator object it is using is not actually the one for the processor
* it is running on.
*
* This class also includes functionality to assist allocators with
* ensuring that requests are aligned according to requests.
*
* Failing to handle this properly will lead to very hard to trace bugs
* where the allocation that caused a GC or allocations immediately following
* GC are run incorrectly.
*/
@Uninterruptible public abstract class Allocator implements Constants {
/**
* Return the space this allocator is currently bound to.
*
* @return The Space.
*/
protected abstract Space getSpace();
/**
* Aligns up an allocation request. The allocation request accepts a
* region, that must be at least particle aligned, an alignment
* request (some power of two number of particles) and an offset (a
* number of particles). There is also a knownAlignment parameter to
* allow a more optimised check when the particular allocator in use
* always aligns at a coarser grain than individual particles, such
* as some free lists.
*
* @param region The region to align up.
* @param alignment The requested alignment
* @param offset The offset from the alignment
* @param knownAlignment The statically known minimum alignment.
* @return The aligned up address.
*/
@Inline
public static Address alignAllocation(Address region, int alignment, int offset, int knownAlignment, boolean fillAlignmentGap) {
if (VM.VERIFY_ASSERTIONS) {
VM.assertions._assert(knownAlignment >= MIN_ALIGNMENT);
VM.assertions._assert(MIN_ALIGNMENT >= BYTES_IN_INT);
VM.assertions._assert(!(fillAlignmentGap && region.isZero()));
VM.assertions._assert(alignment <= MAX_ALIGNMENT);
VM.assertions._assert(offset >= 0);
VM.assertions._assert(region.toWord().and(Word.fromIntSignExtend(MIN_ALIGNMENT-1)).isZero());
VM.assertions._assert((alignment & (MIN_ALIGNMENT - 1)) == 0);
VM.assertions._assert((offset & (MIN_ALIGNMENT - 1)) == 0);
}
// No alignment ever required.
if (alignment <= knownAlignment || MAX_ALIGNMENT <= MIN_ALIGNMENT)
return region;
// May require an alignment
Word mask = Word.fromIntSignExtend(alignment - 1);
Word negOff = Word.fromIntSignExtend(-offset);
Offset delta = negOff.minus(region.toWord()).and(mask).toOffset();
if (fillAlignmentGap && ALIGNMENT_VALUE != 0) {
if ((MAX_ALIGNMENT - MIN_ALIGNMENT) == BYTES_IN_WORD) {
// At most a single hole
if (delta.toInt() == (BYTES_IN_WORD)) {
region.store(Word.fromIntSignExtend(ALIGNMENT_VALUE));
region = region.plus(delta);
return region;
}
} else {
while (delta.toInt() >= (BYTES_IN_WORD)) {
region.store(Word.fromIntSignExtend(ALIGNMENT_VALUE));
region = region.plus(BYTES_IN_WORD);
delta = delta.minus(BYTES_IN_WORD);
}
}
}
return region.plus(delta);
}
/**
* Fill the specified region with the alignment value.
*
* @param start The start of the region.
* @param end A pointer past the end of the region.
*/
@Inline
public static void fillAlignmentGap(Address start, Address end) {
if ((MAX_ALIGNMENT - MIN_ALIGNMENT) == BYTES_IN_INT) {
// At most a single hole
if (!end.diff(start).isZero()) {
start.store(ALIGNMENT_VALUE);
}
} else {
while (start.LT(end)) {
start.store(ALIGNMENT_VALUE);
start = start.plus(BYTES_IN_INT);
}
}
}
/**
* Aligns up an allocation request. The allocation request accepts a
* region, that must be at least particle aligned, an alignment
* request (some power of two number of particles) and an offset (a
* number of particles).
*
* @param region The region to align up.
* @param alignment The requested alignment
* @param offset The offset from the alignment
* @return The aligned up address.
*/
@Inline
public static Address alignAllocation(Address region, int alignment, int offset) {
return alignAllocation(region, alignment, offset, MIN_ALIGNMENT, true);
}
/**
* Aligns up an allocation request. The allocation request accepts a
* region, that must be at least particle aligned, an alignment
* request (some power of two number of particles) and an offset (a
* number of particles).
*
* @param region The region to align up.
* @param alignment The requested alignment
* @param offset The offset from the alignment
* @return The aligned up address.
*/
@Inline
public static Address alignAllocationNoFill(Address region, int alignment, int offset) {
return alignAllocation(region, alignment, offset, MIN_ALIGNMENT, false);
}
/**
* This method calculates the minimum size that will guarantee the allocation
* of a specified number of bytes at the specified alignment.
*
* @param size The number of bytes (not aligned).
* @param alignment The requested alignment (some factor of 2).
*/
@Inline
public static int getMaximumAlignedSize(int size, int alignment) {
return getMaximumAlignedSize(size, alignment, MIN_ALIGNMENT);
}
/**
* This method calculates the minimum size that will guarantee the allocation
* of a specified number of bytes at the specified alignment.
*
* @param size The number of bytes (not aligned).
* @param alignment The requested alignment (some factor of 2).
* @param knownAlignment The known minimum alignment. Specifically for use in
* allocators that enforce greater than particle alignment. It is a <b>precondition</b>
* that size is aligned to knownAlignment, and that knownAlignment >= MIN_ALGINMENT.
*/
@Inline
public static int getMaximumAlignedSize(int size, int alignment, int knownAlignment) {
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(size == Conversions.roundDown(size, knownAlignment));
if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(knownAlignment >= MIN_ALIGNMENT);
if (MAX_ALIGNMENT <= MIN_ALIGNMENT || alignment <= knownAlignment) {
return size;
} else {
return size + alignment - knownAlignment;
}
}
/**
* Single slow path allocation attempt. This is called by allocSlow.
*
* @param bytes The size of the allocation request
* @param alignment The required alignment
* @param offset The alignment offset
* @return The start address of the region, or zero if allocation fails
*/
protected abstract Address allocSlowOnce(int bytes, int alignment, int offset);
/**
* <b>Out-of-line</b> slow path allocation. This method forces slow path
* allocation to be out of line (typically desirable, but not when the
* calling context is already explicitly out-of-line).
*
* @param bytes The size of the allocation request
* @param alignment The required alignment
* @param offset The alignment offset
* @return The start address of the region, or zero if allocation fails
*/
@NoInline
public final Address allocSlow(int bytes, int alignment, int offset) {
return allocSlowInline(bytes, alignment, offset);
}
/**
* <b>Inline</b> slow path allocation. This method attempts allocSlowOnce
* several times, and allows collection to occur, and ensures that execution
* safely resumes by taking care of potential thread/mutator context affinity
* changes. All allocators should use this as the trampoline for slow
* path allocation.
*
* @param bytes The size of the allocation request
* @param alignment The required alignment
* @param offset The alignment offset
* @return The start address of the region, or zero if allocation fails
*/
@Inline
public final Address allocSlowInline(int bytes, int alignment, int offset) {
int gcCountStart = Stats.gcCount();
Allocator current = this;
Space space = current.getSpace();
for (int i = 0; i < Plan.MAX_COLLECTION_ATTEMPTS; i++) {
Address result = current.allocSlowOnce(bytes, alignment, offset);
if (!result.isZero()) {
return result;
}
if (!Plan.gcInProgress()) {
/* This is in case a GC occurs, and our mutator context is stale.
* In some VMs the scheduler can change the affinity between the
* current thread and the mutator context. This is possible for
* VMs that dynamically multiplex Java threads onto multiple mutator
* contexts, */
current = VM.activePlan.mutator().getAllocatorFromSpace(space);
}
}
Log.write("GC Error: Allocator.allocSlow failed on request of ");
Log.write(bytes);
Log.write(" on space ");
Log.writeln(space.getName());
Log.write("gcCountStart = ");
Log.writeln(gcCountStart);
Log.write("gcCount (now) = ");
Log.writeln(Stats.gcCount());
Space.printUsageMB();
VM.assertions.fail("Allocation Failed!");
/* NOTREACHED */
return Address.zero();
}
}