107 lines
4.2 KiB
Java
107 lines
4.2 KiB
Java
/*
|
|
* Copyright (C) 2017 The Android Open Source Project
|
|
*
|
|
* Licensed 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 android.util.apk;
|
|
|
|
import android.system.ErrnoException;
|
|
import android.system.Os;
|
|
import android.system.OsConstants;
|
|
|
|
import java.io.FileDescriptor;
|
|
import java.io.IOException;
|
|
import java.nio.ByteBuffer;
|
|
import java.nio.DirectByteBuffer;
|
|
import java.security.DigestException;
|
|
|
|
/**
|
|
* {@link DataSource} which provides data from a file descriptor by memory-mapping the sections
|
|
* of the file.
|
|
*/
|
|
class MemoryMappedFileDataSource implements DataSource {
|
|
private static final long MEMORY_PAGE_SIZE_BYTES = Os.sysconf(OsConstants._SC_PAGESIZE);
|
|
|
|
private final FileDescriptor mFd;
|
|
private final long mFilePosition;
|
|
private final long mSize;
|
|
|
|
/**
|
|
* Constructs a new {@code MemoryMappedFileDataSource} for the specified region of the file.
|
|
*
|
|
* @param fd file descriptor to read from.
|
|
* @param position start position of the region in the file.
|
|
* @param size size (in bytes) of the region.
|
|
*/
|
|
MemoryMappedFileDataSource(FileDescriptor fd, long position, long size) {
|
|
mFd = fd;
|
|
mFilePosition = position;
|
|
mSize = size;
|
|
}
|
|
|
|
@Override
|
|
public long size() {
|
|
return mSize;
|
|
}
|
|
|
|
@Override
|
|
public void feedIntoDataDigester(DataDigester md, long offset, int size)
|
|
throws IOException, DigestException {
|
|
// IMPLEMENTATION NOTE: After a lot of experimentation, the implementation of this
|
|
// method was settled on a straightforward mmap with prefaulting.
|
|
//
|
|
// This method is not using FileChannel.map API because that API does not offset a way
|
|
// to "prefault" the resulting memory pages. Without prefaulting, performance is about
|
|
// 10% slower on small to medium APKs, but is significantly worse for APKs in 500+ MB
|
|
// range. FileChannel.load (which currently uses madvise) doesn't help. Finally,
|
|
// invoking madvise (MADV_SEQUENTIAL) after mmap with prefaulting wastes quite a bit of
|
|
// time, which is not compensated for by faster reads.
|
|
|
|
// We mmap the smallest region of the file containing the requested data. mmap requires
|
|
// that the start offset in the file must be a multiple of memory page size. We thus may
|
|
// need to mmap from an offset less than the requested offset.
|
|
long filePosition = mFilePosition + offset;
|
|
long mmapFilePosition =
|
|
(filePosition / MEMORY_PAGE_SIZE_BYTES) * MEMORY_PAGE_SIZE_BYTES;
|
|
int dataStartOffsetInMmapRegion = (int) (filePosition - mmapFilePosition);
|
|
long mmapRegionSize = size + dataStartOffsetInMmapRegion;
|
|
long mmapPtr = 0;
|
|
try {
|
|
mmapPtr = Os.mmap(
|
|
0, // let the OS choose the start address of the region in memory
|
|
mmapRegionSize,
|
|
OsConstants.PROT_READ,
|
|
OsConstants.MAP_SHARED | OsConstants.MAP_POPULATE, // "prefault" all pages
|
|
mFd,
|
|
mmapFilePosition);
|
|
ByteBuffer buf = new DirectByteBuffer(
|
|
size,
|
|
mmapPtr + dataStartOffsetInMmapRegion,
|
|
mFd, // not really needed, but just in case
|
|
null, // no need to clean up -- it's taken care of by the finally block
|
|
true // read only buffer
|
|
);
|
|
md.consume(buf);
|
|
} catch (ErrnoException e) {
|
|
throw new IOException("Failed to mmap " + mmapRegionSize + " bytes", e);
|
|
} finally {
|
|
if (mmapPtr != 0) {
|
|
try {
|
|
Os.munmap(mmapPtr, mmapRegionSize);
|
|
} catch (ErrnoException ignored) { }
|
|
}
|
|
}
|
|
}
|
|
}
|