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[Java] allowing larger buffer sizes when growing a byte buffer (#6118)

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Related with issue #6113.

`(old_buf_size & 0xC0000000) != 0` checks if we can duplicate old_buf_size
 and still be under 2GB (by checking if bit 30 or 31 is 1). This doesn't
allow buffers larger than 1GB.

The strategy now is to allocate a buffer with the maximum array size
when we detect that we are overflowing the 2GB.

Also changed default buffer size to 1024.
This commit is contained in:
Diogo Monteiro
2020-09-17 19:55:24 +01:00
committed by GitHub
parent 89435303b7
commit f96d1ef744
1 changed files with 28 additions and 5 deletions
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33
java/com/google/flatbuffers/FlatBufferBuilder.java
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@@ -53,6 +53,19 @@ public class FlatBufferBuilder {
Map<String, Integer> string_pool; // map used to cache shared strings.
/// @endcond
/**
* Maximum size of buffer to allocate. If we're allocating arrays on the heap,
* the header size of the array counts towards its maximum size.
*/
private static final int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
/**
* Default buffer size that is allocated if an initial size is not given, or is
* non positive.
*/
private static final int DEFAULT_BUFFER_SIZE = 1024;
/**
* Start with a buffer of size `initial_size`, then grow as required.
*
@@ -74,7 +87,7 @@ public class FlatBufferBuilder {
public FlatBufferBuilder(int initial_size, ByteBufferFactory bb_factory,
ByteBuffer existing_bb, Utf8 utf8) {
if (initial_size <= 0) {
initial_size = 1;
initial_size = DEFAULT_BUFFER_SIZE;
}
this.bb_factory = bb_factory;
if (existing_bb != null) {
@@ -101,7 +114,7 @@ public class FlatBufferBuilder {
* Start with a buffer of 1KiB, then grow as required.
*/
public FlatBufferBuilder() {
this(1024);
this(DEFAULT_BUFFER_SIZE);
}
/**
@@ -247,9 +260,19 @@ public class FlatBufferBuilder {
*/
static ByteBuffer growByteBuffer(ByteBuffer bb, ByteBufferFactory bb_factory) {
int old_buf_size = bb.capacity();
if ((old_buf_size & 0xC0000000) != 0) // Ensure we don't grow beyond what fits in an int.
throw new AssertionError("FlatBuffers: cannot grow buffer beyond 2 gigabytes.");
int new_buf_size = old_buf_size == 0 ? 1 : old_buf_size << 1;
int new_buf_size;
if (old_buf_size == 0) {
new_buf_size = DEFAULT_BUFFER_SIZE;
}
else {
if (old_buf_size == MAX_BUFFER_SIZE) { // Ensure we don't grow beyond what fits in an int.
throw new AssertionError("FlatBuffers: cannot grow buffer beyond 2 gigabytes.");
}
new_buf_size = (old_buf_size & 0xC0000000) != 0 ? MAX_BUFFER_SIZE : old_buf_size << 1;
}
bb.position(0);
ByteBuffer nbb = bb_factory.newByteBuffer(new_buf_size);
new_buf_size = nbb.clear().capacity(); // Ensure the returned buffer is treated as empty