I've been beating my head against the wall trying to figure out which
file I/O techniques work at speeds comparable to their Java SDK
counterparts, and which don't. I've run benchmarks which indicate,
for example, that a batch operation on a memory mapped ByteBuffer runs
at 1/5 the speed of byte-at-a-time operations on an array-backed
ByteBuffer. Byte-at-a-time I/O on random access files is more than
100 times slower than other techniques. I've included my benchmark
method and its output (as run on a 2.8MB file on a HTC G1 with Android
1.1) below.
My primary questions are:
1) Has anybody else worked through various I/O techniques under
Android and figured out which are usable and which are too inefficient
to bother with?
2) Can I expect these libraries to be significantly more efficient in
Android 1.5?
Question (2) is the really important one. I'll rewrite my apps for
efficiency if I have to, but if the issue is going to be rendered moot
in a matter of weeks, I'd rather not go to quite as much trouble.
-Beekeeper
---
public void testReading(final RandomAccessFile in) throws
IOException {
// Allocate files and objects outside of timing loops
final FileChannel channel = in.getChannel();
final int fileSize = (int)channel.size();
final byte[] testBytes = new byte[fileSize];
final ByteBuffer buff = ByteBuffer.allocate(fileSize);
final byte[] buffArray = buff.array();
final int buffBase = buff.arrayOffset();
// Read from channel into buffer, and batch read from buffer to
byte array
long time1 = System.currentTimeMillis();
channel.position(0);
channel.read(buff);
buff.flip();
buff.get(testBytes);
long time2 = System.currentTimeMillis();
System.out.println("Fast load: " + (time2 - time1) + "ms");
// Read from channel into buffer, and batch copy from underlying
array
time1 = System.currentTimeMillis();
channel.position(0);
channel.read(buff);
buff.flip();
System.arraycopy(buffArray, buffBase, testBytes, 0,
testBytes.length);
time2 = System.currentTimeMillis();
System.out.println("Another fast load: " + (time2 - time1) +
"ms");
// Read from channel into buffer, and get bytes one-by-one from
underlying array
time1 = System.currentTimeMillis();
channel.position(0);
channel.read(buff);
buff.flip();
for (int i = 0, j = buffBase, ni = testBytes.length; i < ni; i++, j
++)
testBytes[i] = buffArray[j];
time2 = System.currentTimeMillis();
System.out.println("Fastish load: " + (time2 - time1) + "ms");
// Read from channel into buffer, and get bytes one-by-one
time1 = System.currentTimeMillis();
channel.position(0);
channel.read(buff);
buff.flip();
for (int i = 0, ni = testBytes.length; i < ni; i++)
testBytes[i] = buff.get();
buff.flip();
time2 = System.currentTimeMillis();
System.out.println("Medium load: " + (time2 - time1) + "ms");
// Memory map buffer, and batch read from buffer to byte array
time1 = System.currentTimeMillis();
final MappedByteBuffer buff2 = channel.map(MapMode.READ_WRITE, 0,
fileSize);
buff2.get(testBytes);
buff2.flip();
time2 = System.currentTimeMillis();
System.out.println("Slow load: " + (time2 - time1) + "ms");
// Read bytes one-by-one, directly from file
time1 = System.currentTimeMillis();
in.seek(0);
for (int i = 0, ni = testBytes.length; i < ni; i++)
testBytes[i] = (byte)in.read();
time2 = System.currentTimeMillis();
System.out.println("Incredibly slow load: " + (time2 - time1) +
"ms");
}
---
I/System.out(12168): Fast load: 83ms
I/System.out(12168): Another fast load: 23ms
I/System.out(12168): Fastish load: 1497ms
I/System.out(12168): Medium load: 5507ms
I/System.out(12168): Slow load: 32165ms
D/dalvikvm(12168): GC freed 87347 objects / 2097056 bytes in 242ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 250ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 242ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 249ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 247ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 249ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 242ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 252ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 243ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 249ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 243ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 249ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 243ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 249ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 242ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 250ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 243ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 249ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 245ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 251ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 242ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 250ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 242ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 249ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 244ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 249ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 243ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 250ms
D/dalvikvm(12168): GC freed 87367 objects / 2097144 bytes in 243ms
D/dalvikvm(12168): GC freed 87367 objects / 2097152 bytes in 251ms
I/System.out(12168): Incredibly slow load: 446546ms
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