RFR 8193832: Performance of InputStream.readAllBytes() could be improved (original) (raw)

Brian Burkhalter brian.burkhalter at oracle.com
Tue Dec 19 21:43:28 UTC 2017

On Dec 19, 2017, at 12:52 PM, Paul Sandoz <paul.sandoz at oracle.com> wrote:

For the case of reading 2^N bytes i believe you can avoid doing a last copy by checking if “n < 0" within the “nread > 0” block when “nread == DEAFULTBUFFERSIZE”. That might close the perf gap for smaller cases. You can also move "nread = 0” to the same block e.g.:

var copy = (n < 0 && nread == DEAFULTBUFFERSIZE) ? buf : Arrays.copyOf(buf, nread); list.add(copy) nread = 0;

Definitely improves performance and memory footprint for this case.

262 byte[] output = new byte[total]; 263 int offset = 0; 264 int numCached = list.size(); 265 for (int i = 0; i < numCached; i++) { 266 byte[] b = list.get(i); 267 System.arraycopy(b, 0, output, offset, b.length); 268 offset += b.length; 269 }

You can simplify to: var result = new byte[total]; int offset = 0; for (buf : list) { System.arraycopy(buf, 0, result, offset, buf.length); offset += buf.length; }

Oh, yes, of course.

s/list/bufs and then you can use var for the declarations at the start of the method.

Done. Updated: http://cr.openjdk.java.net/~bpb/8193832/webrev.01/

Good suggestions! Not sure however about line 237 as with var it has to be “var n = 0;” instead of simply “int n;” with no initialization. Also I’ve not tested the effect of the initial List capacity at line 233: the current value of 128 is arbitrary - might be better to go with the default?

Thanks,

Brian

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