8193832: Performance of InputStream.readAllBytes() could be improved
Summary: Read into a list of fixed-size buffers which are gathered at the end
Reviewed-by: alanb, chegar, plevart, jrose, psandoz
--- a/src/java.base/share/classes/java/io/InputStream.java Fri Dec 22 15:23:34 2017 -0500
+++ b/src/java.base/share/classes/java/io/InputStream.java Fri Dec 22 14:00:03 2017 -0800
@@ -25,7 +25,9 @@
package java.io;
+import java.util.ArrayList;
import java.util.Arrays;
+import java.util.List;
import java.util.Objects;
/**
@@ -229,30 +231,55 @@
* @since 9
*/
public byte[] readAllBytes() throws IOException {
- byte[] buf = new byte[DEFAULT_BUFFER_SIZE];
- int capacity = buf.length;
- int nread = 0;
+ List<byte[]> bufs = null;
+ byte[] result = null;
+ int total = 0;
int n;
- for (;;) {
- // read to EOF which may read more or less than initial buffer size
- while ((n = read(buf, nread, capacity - nread)) > 0)
+ do {
+ byte[] buf = new byte[DEFAULT_BUFFER_SIZE];
+ int nread = 0;
+
+ // read to EOF which may read more or less than buffer size
+ while ((n = read(buf, nread, buf.length - nread)) > 0) {
nread += n;
+ }
- // if the last call to read returned -1, then we're done
- if (n < 0)
- break;
+ if (nread > 0) {
+ if (MAX_BUFFER_SIZE - total < nread) {
+ throw new OutOfMemoryError("Required array size too large");
+ }
+ total += nread;
+ if (result == null) {
+ result = buf;
+ } else {
+ if (bufs == null) {
+ bufs = new ArrayList<>();
+ bufs.add(result);
+ }
+ bufs.add(buf);
+ }
+ }
+ } while (n >= 0); // if the last call to read returned -1, then break
- // need to allocate a larger buffer
- if (capacity <= MAX_BUFFER_SIZE - capacity) {
- capacity = capacity << 1;
- } else {
- if (capacity == MAX_BUFFER_SIZE)
- throw new OutOfMemoryError("Required array size too large");
- capacity = MAX_BUFFER_SIZE;
+ if (bufs == null) {
+ if (result == null) {
+ return new byte[0];
}
- buf = Arrays.copyOf(buf, capacity);
+ return result.length == total ?
+ result : Arrays.copyOf(result, total);
}
- return (capacity == nread) ? buf : Arrays.copyOf(buf, nread);
+
+ result = new byte[total];
+ int offset = 0;
+ int remaining = total;
+ for (byte[] b : bufs) {
+ int len = Math.min(b.length, remaining);
+ System.arraycopy(b, 0, result, offset, len);
+ offset += len;
+ remaining -= len;
+ }
+
+ return result;
}
/**
--- a/test/jdk/java/io/InputStream/ReadAllBytes.java Fri Dec 22 15:23:34 2017 -0500
+++ b/test/jdk/java/io/InputStream/ReadAllBytes.java Fri Dec 22 14:00:03 2017 -0800
@@ -31,7 +31,7 @@
/*
* @test
- * @bug 8080835
+ * @bug 8080835 8193832
* @library /test/lib
* @build jdk.test.lib.RandomFactory
* @run main ReadAllBytes
@@ -47,15 +47,11 @@
test(new byte[]{});
test(new byte[]{1, 2, 3});
test(createRandomBytes(1024));
- test(createRandomBytes((1 << 13) - 1));
- test(createRandomBytes((1 << 13)));
- test(createRandomBytes((1 << 13) + 1));
- test(createRandomBytes((1 << 15) - 1));
- test(createRandomBytes((1 << 15)));
- test(createRandomBytes((1 << 15) + 1));
- test(createRandomBytes((1 << 17) - 1));
- test(createRandomBytes((1 << 17)));
- test(createRandomBytes((1 << 17) + 1));
+ for (int shift : new int[] {13, 14, 15, 17}) {
+ for (int offset : new int[] {-1, 0, 1}) {
+ test(createRandomBytes((1 << shift) + offset));
+ }
+ }
}
static void test(byte[] expectedBytes) throws IOException {