Github user julienledem commented on a diff in the pull request:
https://github.com/apache/drill/pull/283#discussion_r46225897
--- Diff:
exec/memory/base/src/main/java/org/apache/drill/exec/memory/AllocationReservation.java
---
@@ -0,0 +1,155 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.drill.exec.memory;
+
+import io.netty.buffer.DrillBuf;
+
+import com.google.common.base.Preconditions;
+
+/**
+ * Supports cumulative allocation reservation. Clients may increase the
size of the reservation repeatedly until they
+ * call for an allocation of the current total size. The reservation can
only be used once, and will throw an exception
+ * if it is used more than once.
+ * <p>
+ * For the purposes of airtight memory accounting, the reservation must be
close()d whether it is used or not.
+ * This is not threadsafe.
+ */
+public abstract class AllocationReservation implements AutoCloseable {
+ private int nBytes = 0;
+ private boolean used = false;
+ private boolean closed = false;
+
+ /**
+ * Constructor. Prevent construction except by derived classes.
+ * <p>The expectation is that the derived class will be a non-static
inner
+ * class in an allocator.
+ */
+ AllocationReservation() {
+ }
+
+ /**
+ * Add to the current reservation.
+ *
+ * <p>Adding may fail if the allocator is not allowed to consume any
more space.
+ *
+ * @param nBytes the number of bytes to add
+ * @return true if the addition is possible, false otherwise
+ * @throws IllegalStateException if called after buffer() is used to
allocate the reservation
+ */
+ public boolean add(final int nBytes) {
+ Preconditions.checkArgument(nBytes >= 0, "nBytes(%d) < 0", nBytes);
+ Preconditions.checkState(!closed, "Attempt to increase reservation
after reservation has been closed");
+ Preconditions.checkState(!used, "Attempt to increase reservation after
reservation has been used");
+
+ // we round up to next power of two since all reservations are done in
powers of two. This may overestimate the
+ // preallocation since someone may perceive additions to be power of
two. If this becomes a problem, we can look at
+ // modifying this behavior so that we maintain what we reserve and
what the user asked for and make sure to only
+ // round to power of two as necessary.
+ final int nBytesTwo = BaseAllocator.nextPowerOfTwo(nBytes);
+ if (!reserve(nBytesTwo)) {
+ return false;
+ }
+
+ this.nBytes += nBytesTwo;
+ return true;
+ }
+
+ /**
+ * Requests a reservation of additional space.
+ *
+ * <p>The implementation of the allocator's inner class provides this.
+ *
+ * @param nBytes the amount to reserve
+ * @return true if the reservation can be satisfied, false otherwise
+ */
+ abstract boolean reserve(int nBytes);
+
+ /**
+ * Allocate a buffer whose size is the total of all the add()s made.
+ *
+ * <p>The allocation request can still fail, even if the amount of space
+ * requested is available, if the allocation cannot be made contiguously.
+ *
+ * @return the buffer, or null, if the request cannot be satisfied
+ * @throws IllegalStateException if called called more than once
+ */
+ public DrillBuf buffer() {
--- End diff --
methods should be a verb. How about allocateBuffer() ?
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