Hi Paul, Following up with the requested loop and vectorization benchmarks ... (Do the vectorization benchmark results imply that the Hotspot compiler has been unable to perform the vectorization optimisation due to the presence of the reachabilityFence ?) ----------------------------------------------------------------------------------------------------------------------- Loop Benchmarking ---- ------------ package org.sample; import org.openjdk.jmh.annotations.Benchmark; import org.openjdk.jmh.annotations.Level; import org.openjdk.jmh.annotations.Param; import org.openjdk.jmh.annotations.Scope; import org.openjdk.jmh.annotations.Setup; import org.openjdk.jmh.annotations.State; import java.nio.ByteBuffer; @State(Scope.Benchmark) public class ByteBufferBenchmark { @Param({"1", "10", "100", "1000", "10000"}) public int L; @State(Scope.Benchmark) public static class ByteBufferContainer { ByteBuffer bb; @Setup(Level.Invocation) public void initByteBuffer() { bb = ByteBuffer.allocateDirect(10000); } ByteBuffer getByteBuffer() { return bb; } } @Benchmark public ByteBuffer benchmark_byte_buffer_put(ByteBufferContainer bbC) { ByteBuffer bb = bbC.getByteBuffer(); for (int i = 0; i < L; i++) { bb.put((byte)i); } return bb; } } Without Changes Benchmark (L) Mode Cnt Score Error Units ByteBufferBenchmark.benchmark_byte_buffer_put 1 thrpt 200 29303145.752 ± 635979.750 ops/s ByteBufferBenchmark.benchmark_byte_buffer_put 10 thrpt 200 24260859.017 ± 528891.303 ops/s ByteBufferBenchmark.benchmark_byte_buffer_put 100 thrpt 200 8512366.637 ± 136615.070 ops/s ByteBufferBenchmark.benchmark_byte_buffer_put 1000 thrpt 200 1323756.037 ± 21485.369 ops/s ByteBufferBenchmark.benchmark_byte_buffer_put 10000 thrpt 200 145965.305 ± 1301.469 ops/s With Changes Benchmark (L) Mode Cnt Score Error Units Impact ByteBufferBenchmark.benchmark_byte_buffer_put 1 thrpt 200 28893540.122 ± 754554.747 ops/s -1.398% ByteBufferBenchmark.benchmark_byte_buffer_put 10 thrpt 200 15317696.355 ± 231621.608 ops/s -36.863% ByteBufferBenchmark.benchmark_byte_buffer_put 100 thrpt 200 2546599.578 ± 32136.873 ops/s -70.084% ByteBufferBenchmark.benchmark_byte_buffer_put 1000 thrpt 200 288832.514 ± 3854.522 ops/s -78.181% ByteBufferBenchmark.benchmark_byte_buffer_put 10000 thrpt 200 29747.386 ± 214.831 ops/s -79.620% ----------------------------------------------------------------------------------------------------------------------- Vectorization Benchmarking ------------- ------------ package org.sample; import org.openjdk.jmh.annotations.Benchmark; import org.openjdk.jmh.annotations.Level; import org.openjdk.jmh.annotations.Param; import org.openjdk.jmh.annotations.Scope; import org.openjdk.jmh.annotations.Setup; import org.openjdk.jmh.annotations.State; import java.nio.ByteBuffer; @State(Scope.Benchmark) public class ByteBufferBenchmark { @Param({"1", "10", "100", "1000", "10000"}) public int L; @State(Scope.Benchmark) public static class ByteBufferContainer { ByteBuffer bb; @Setup(Level.Invocation) public void initByteBuffer() { bb = ByteBuffer.allocateDirect(4 * 10000); for (int i = 0; i < 10000; i++) { bb.putInt(i); } } ByteBuffer getByteBuffer() { return bb; } } @Benchmark public int benchmark_byte_buffer_put(ByteBufferContainer bbC) { ByteBuffer bb = bbC.getByteBuffer(); bb.position(0); int sum = 0; for (int i = 0; i < L; i++) { sum += bb.getInt(); } return sum; } } Without Changes Benchmark (L) Mode Cnt Score Error Units ByteBufferBenchmark.benchmark_byte_buffer_put 1 thrpt 200 29677205.748 ± 544721.142 ops/s ByteBufferBenchmark.benchmark_byte_buffer_put 10 thrpt 200 18219951.454 ± 320724.793 ops/s ByteBufferBenchmark.benchmark_byte_buffer_put 100 thrpt 200 7767650.826 ± 121798.910 ops/s ByteBufferBenchmark.benchmark_byte_buffer_put 1000 thrpt 200 1646075.010 ± 9804.499 ops/s ByteBufferBenchmark.benchmark_byte_buffer_put 10000 thrpt 200 183489.418 ± 1355.967 ops/s With Changes Benchmark (L) Mode Cnt Score Error Units Impact ByteBufferBenchmark.benchmark_byte_buffer_put 1 thrpt 200 15230086.695 ± 390174.190 ops/s -48.681% ByteBufferBenchmark.benchmark_byte_buffer_put 10 thrpt 200 8126310.728 ± 123661.342 ops/s -55.399% ByteBufferBenchmark.benchmark_byte_buffer_put 100 thrpt 200 1582699.233 ± 7278.744 ops/s -79.624% ByteBufferBenchmark.benchmark_byte_buffer_put 1000 thrpt 200 179726.465 ± 802.333 ops/s -89.082% ByteBufferBenchmark.benchmark_byte_buffer_put 10000 thrpt 200 18327.049 ± 9.506 ops/s -90.012% NB : For reference - for this and previous benchmarking results ... "Without Changes" and "With Changes" - java -version ... openjdk version "10-internal" 2018-03-20 OpenJDK Runtime Environment (build 10-internal+0-adhoc.walshbp.jdk) OpenJDK 64-Bit Server VM (build 10-internal+0-adhoc.walshbp.jdk, mixed mode) ----------------------------------------------------------------------------------------------------------------------- Regards, Ben Walsh From: Ben Walsh/UK/IBM To: Paul Sandoz <paul.sandoz@oracle.com> Cc: core-libs-dev <core-libs-dev@openjdk.java.net> Date: 05/02/2018 16:47 Subject: Re: [PATCH] Reduce Chance Of Mistakenly Early Backing Memory Cleanup Running with the following test under the JMH benchmark framework (never used this before, so please do point out any issues with the test) ... ------------------------------------------------------------------------------------------------------------------- package org.sample; import org.openjdk.jmh.annotations.Benchmark; import org.openjdk.jmh.annotations.Level; import org.openjdk.jmh.annotations.Scope; import org.openjdk.jmh.annotations.Setup; import org.openjdk.jmh.annotations.State; import java.nio.ByteBuffer; public class ByteBufferBenchmark { @State(Scope.Benchmark) public static class ByteBufferContainer { ByteBuffer bb; @Setup(Level.Invocation) public void initByteBuffer() { bb = ByteBuffer.allocateDirect(1); } ByteBuffer getByteBuffer() { return bb; } } @Benchmark public void benchmark_byte_buffer_put(ByteBufferContainer bbC) { bbC.getByteBuffer().put((byte)42); } } ------------------------------------------------------------------------------------------------------------------- ... I get the following results with and without the changes ... [9walsbp@dolphin ~]$ ./build_with/jdk/bin/java -jar benchmarks.jar WARNING: An illegal reflective access operation has occurred WARNING: Illegal reflective access by org.openjdk.jmh.util.Utils (file:/home/9walsbp/benchmarks.jar) to field java.io.Console.cs WARNING: Please consider reporting this to the maintainers of org.openjdk.jmh.util.Utils WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations WARNING: All illegal access operations will be denied in a future release # JMH version: 1.20 # VM version: JDK 10-internal, VM 10-internal+0-adhoc.walshbp.jdk # VM invoker: /home/9walsbp/build_with/jdk/bin/java # VM options: <none> # Warmup: 20 iterations, 1 s each # Measurement: 20 iterations, 1 s each # Timeout: 10 min per iteration # Threads: 1 thread, will synchronize iterations # Benchmark mode: Throughput, ops/time # Benchmark: org.sample.ByteBufferBenchmark.benchmark_byte_buffer_put # Run progress: 0.00% complete, ETA 00:06:40 # Fork: 1 of 10 # Warmup Iteration 1: 28572294.700 ops/s # Warmup Iteration 2: 33102015.934 ops/s # Warmup Iteration 3: 32883031.968 ops/s # Warmup Iteration 4: 32875302.586 ops/s # Warmup Iteration 5: 33708018.941 ops/s # Warmup Iteration 6: 34107603.885 ops/s # Warmup Iteration 7: 31615123.362 ops/s # Warmup Iteration 8: 34306874.876 ops/s # Warmup Iteration 9: 32615070.232 ops/s # Warmup Iteration 10: 34268641.323 ops/s # Warmup Iteration 11: 32209257.766 ops/s # Warmup Iteration 12: 34111408.999 ops/s # Warmup Iteration 13: 33527360.187 ops/s # Warmup Iteration 14: 34331726.136 ops/s # Warmup Iteration 15: 34325119.218 ops/s # Warmup Iteration 16: 31562168.904 ops/s # Warmup Iteration 17: 33227878.358 ops/s # Warmup Iteration 18: 34151154.273 ops/s # Warmup Iteration 19: 29264381.793 ops/s # Warmup Iteration 20: 30308058.560 ops/s Iteration 1: 33502237.659 ops/s Iteration 2: 33591469.068 ops/s Iteration 3: 29330487.674 ops/s Iteration 4: 31401627.173 ops/s Iteration 5: 32346391.980 ops/s Iteration 6: 34106932.868 ops/s Iteration 7: 29961218.721 ops/s Iteration 8: 31166503.731 ops/s Iteration 9: 34180826.531 ops/s Iteration 10: 34436432.202 ops/s Iteration 11: 28003272.167 ops/s Iteration 12: 30947688.218 ops/s Iteration 13: 33727404.696 ops/s Iteration 14: 33794727.241 ops/s Iteration 15: 34089932.945 ops/s Iteration 16: 30229615.627 ops/s Iteration 17: 32747950.250 ops/s Iteration 18: 34195332.494 ops/s Iteration 19: 34225966.793 ops/s Iteration 20: 30253949.366 ops/s # Run progress: 10.00% complete, ETA 00:27:45 # Fork: 2 of 10 # Warmup Iteration 1: 28189458.524 ops/s # Warmup Iteration 2: 33385943.637 ops/s # Warmup Iteration 3: 31474459.740 ops/s # Warmup Iteration 4: 32994555.969 ops/s # Warmup Iteration 5: 33580210.619 ops/s # Warmup Iteration 6: 34030937.323 ops/s # Warmup Iteration 7: 31891882.950 ops/s # Warmup Iteration 8: 34277935.152 ops/s # Warmup Iteration 9: 31636968.061 ops/s # Warmup Iteration 10: 34376216.983 ops/s # Warmup Iteration 11: 31790184.297 ops/s # Warmup Iteration 12: 34069806.835 ops/s # Warmup Iteration 13: 31737398.413 ops/s # Warmup Iteration 14: 34450863.223 ops/s # Warmup Iteration 15: 34568522.458 ops/s # Warmup Iteration 16: 30029081.882 ops/s # Warmup Iteration 17: 32092783.620 ops/s # Warmup Iteration 18: 33063366.197 ops/s # Warmup Iteration 19: 27694130.000 ops/s # Warmup Iteration 20: 31264525.792 ops/s Iteration 1: 33330874.247 ops/s Iteration 2: 34150690.011 ops/s Iteration 3: 28497705.592 ops/s Iteration 4: 31877639.021 ops/s Iteration 5: 33367324.280 ops/s Iteration 6: 34472176.807 ops/s Iteration 7: 29032738.714 ops/s Iteration 8: 31544864.097 ops/s Iteration 9: 33752028.095 ops/s Iteration 10: 34473732.353 ops/s Iteration 11: 29982974.569 ops/s Iteration 12: 30603336.272 ops/s Iteration 13: 32481117.249 ops/s Iteration 14: 33393570.191 ops/s Iteration 15: 34358979.713 ops/s Iteration 16: 27617909.839 ops/s Iteration 17: 30833802.394 ops/s Iteration 18: 32004461.408 ops/s Iteration 19: 34074910.495 ops/s Iteration 20: 34346053.320 ops/s # Run progress: 20.00% complete, ETA 00:24:26 # Fork: 3 of 10 # Warmup Iteration 1: 28503366.982 ops/s # Warmup Iteration 2: 33475519.627 ops/s # Warmup Iteration 3: 34588321.205 ops/s # Warmup Iteration 4: 35947256.417 ops/s # Warmup Iteration 5: 37638512.766 ops/s # Warmup Iteration 6: 38208797.422 ops/s # Warmup Iteration 7: 32824617.800 ops/s # Warmup Iteration 8: 35767442.077 ops/s # Warmup Iteration 9: 36548126.754 ops/s # Warmup Iteration 10: 38337143.976 ops/s # Warmup Iteration 11: 35379051.550 ops/s # Warmup Iteration 12: 38381933.847 ops/s # Warmup Iteration 13: 36543582.434 ops/s # Warmup Iteration 14: 38178008.316 ops/s # Warmup Iteration 15: 38213974.988 ops/s # Warmup Iteration 16: 32176964.179 ops/s # Warmup Iteration 17: 35487842.133 ops/s # Warmup Iteration 18: 38381350.345 ops/s # Warmup Iteration 19: 31504263.357 ops/s # Warmup Iteration 20: 37831665.793 ops/s Iteration 1: 37530637.288 ops/s Iteration 2: 38628685.180 ops/s Iteration 3: 35170239.750 ops/s Iteration 4: 32397535.287 ops/s Iteration 5: 38643366.565 ops/s Iteration 6: 35723555.410 ops/s Iteration 7: 37073023.139 ops/s Iteration 8: 38332509.859 ops/s Iteration 9: 36047299.714 ops/s Iteration 10: 38666580.432 ops/s Iteration 11: 38827527.980 ops/s Iteration 12: 38885170.177 ops/s Iteration 13: 38552899.367 ops/s Iteration 14: 38231144.659 ops/s Iteration 15: 26785494.819 ops/s Iteration 16: 35979289.874 ops/s Iteration 17: 36233311.409 ops/s Iteration 18: 37322531.784 ops/s Iteration 19: 30917505.079 ops/s Iteration 20: 36602131.217 ops/s # Run progress: 30.00% complete, ETA 00:19:56 # Fork: 4 of 10 # Warmup Iteration 1: 28201486.347 ops/s # Warmup Iteration 2: 33954913.216 ops/s # Warmup Iteration 3: 33614818.543 ops/s # Warmup Iteration 4: 36075462.255 ops/s # Warmup Iteration 5: 35868466.813 ops/s # Warmup Iteration 6: 37539151.611 ops/s # Warmup Iteration 7: 35791698.290 ops/s # Warmup Iteration 8: 37804228.841 ops/s # Warmup Iteration 9: 36209952.096 ops/s # Warmup Iteration 10: 37995654.523 ops/s # Warmup Iteration 11: 36279556.807 ops/s # Warmup Iteration 12: 37876471.909 ops/s # Warmup Iteration 13: 35472820.096 ops/s # Warmup Iteration 14: 38192862.745 ops/s # Warmup Iteration 15: 38214750.954 ops/s # Warmup Iteration 16: 33616490.113 ops/s # Warmup Iteration 17: 37147216.192 ops/s # Warmup Iteration 18: 37759898.719 ops/s # Warmup Iteration 19: 31762576.627 ops/s # Warmup Iteration 20: 35935371.693 ops/s Iteration 1: 37612237.054 ops/s Iteration 2: 31182849.622 ops/s Iteration 3: 35771979.960 ops/s Iteration 4: 37617025.341 ops/s Iteration 5: 31274273.020 ops/s Iteration 6: 36798699.672 ops/s Iteration 7: 37923256.148 ops/s Iteration 8: 38143822.112 ops/s Iteration 9: 29781444.210 ops/s Iteration 10: 34202436.254 ops/s Iteration 11: 36538073.378 ops/s Iteration 12: 37944072.150 ops/s Iteration 13: 30172512.287 ops/s Iteration 14: 34294490.289 ops/s Iteration 15: 37096818.141 ops/s Iteration 16: 37884541.579 ops/s Iteration 17: 31627891.962 ops/s Iteration 18: 34458196.904 ops/s Iteration 19: 37949147.371 ops/s Iteration 20: 38084720.812 ops/s # Run progress: 40.00% complete, ETA 00:17:39 # Fork: 5 of 10 # Warmup Iteration 1: 26430556.314 ops/s # Warmup Iteration 2: 28702874.225 ops/s # Warmup Iteration 3: 28012568.331 ops/s # Warmup Iteration 4: 30857741.012 ops/s # Warmup Iteration 5: 30671764.934 ops/s # Warmup Iteration 6: 31729981.637 ops/s # Warmup Iteration 7: 30171277.707 ops/s # Warmup Iteration 8: 29817290.663 ops/s # Warmup Iteration 9: 31275042.135 ops/s # Warmup Iteration 10: 32028867.062 ops/s # Warmup Iteration 11: 30066034.279 ops/s # Warmup Iteration 12: 30772389.223 ops/s # Warmup Iteration 13: 30066233.182 ops/s # Warmup Iteration 14: 32035909.235 ops/s # Warmup Iteration 15: 32192119.140 ops/s # Warmup Iteration 16: 30496387.577 ops/s # Warmup Iteration 17: 30957378.046 ops/s # Warmup Iteration 18: 31420314.443 ops/s # Warmup Iteration 19: 31981518.074 ops/s # Warmup Iteration 20: 26748312.384 ops/s Iteration 1: 28740606.592 ops/s Iteration 2: 30156532.719 ops/s Iteration 3: 31775304.195 ops/s Iteration 4: 26843600.302 ops/s Iteration 5: 30284709.884 ops/s Iteration 6: 32124615.948 ops/s Iteration 7: 32123075.530 ops/s Iteration 8: 26454319.079 ops/s Iteration 9: 31913402.742 ops/s Iteration 10: 32437412.737 ops/s Iteration 11: 32164716.512 ops/s Iteration 12: 25373082.559 ops/s Iteration 13: 30293078.502 ops/s Iteration 14: 31128369.793 ops/s Iteration 15: 31415561.253 ops/s Iteration 16: 32120636.468 ops/s Iteration 17: 25984394.598 ops/s Iteration 18: 30199573.863 ops/s Iteration 19: 32556187.120 ops/s Iteration 20: 32636129.190 ops/s # Run progress: 50.00% complete, ETA 00:14:30 # Fork: 6 of 10 # Warmup Iteration 1: 28150411.806 ops/s # Warmup Iteration 2: 28054601.733 ops/s # Warmup Iteration 3: 33178455.042 ops/s # Warmup Iteration 4: 33339230.141 ops/s # Warmup Iteration 5: 33332791.104 ops/s # Warmup Iteration 6: 33624536.190 ops/s # Warmup Iteration 7: 31299303.684 ops/s # Warmup Iteration 8: 33037261.267 ops/s # Warmup Iteration 9: 33356211.045 ops/s # Warmup Iteration 10: 33861930.201 ops/s # Warmup Iteration 11: 33270425.776 ops/s # Warmup Iteration 12: 33692415.570 ops/s # Warmup Iteration 13: 33297727.491 ops/s # Warmup Iteration 14: 33820015.956 ops/s # Warmup Iteration 15: 33808521.564 ops/s # Warmup Iteration 16: 31213861.694 ops/s # Warmup Iteration 17: 32149452.446 ops/s # Warmup Iteration 18: 33684868.956 ops/s # Warmup Iteration 19: 30155197.410 ops/s # Warmup Iteration 20: 33566808.050 ops/s Iteration 1: 33654501.647 ops/s Iteration 2: 29509826.671 ops/s Iteration 3: 29610518.398 ops/s Iteration 4: 32646220.404 ops/s Iteration 5: 33773773.299 ops/s Iteration 6: 27873055.802 ops/s Iteration 7: 30681259.230 ops/s Iteration 8: 32717634.647 ops/s Iteration 9: 33758469.696 ops/s Iteration 10: 27232349.464 ops/s Iteration 11: 30616039.535 ops/s Iteration 12: 31682354.340 ops/s Iteration 13: 32580910.390 ops/s Iteration 14: 33811388.262 ops/s Iteration 15: 27191817.186 ops/s Iteration 16: 29873209.932 ops/s Iteration 17: 32087557.824 ops/s Iteration 18: 32644007.761 ops/s Iteration 19: 33799135.934 ops/s Iteration 20: 26758101.989 ops/s # Run progress: 60.00% complete, ETA 00:11:43 # Fork: 7 of 10 # Warmup Iteration 1: 26592644.866 ops/s # Warmup Iteration 2: 33131524.362 ops/s # Warmup Iteration 3: 30127771.163 ops/s # Warmup Iteration 4: 31924144.092 ops/s # Warmup Iteration 5: 32001599.069 ops/s # Warmup Iteration 6: 33648812.429 ops/s # Warmup Iteration 7: 30874748.951 ops/s # Warmup Iteration 8: 33802650.338 ops/s # Warmup Iteration 9: 31054184.796 ops/s # Warmup Iteration 10: 33484369.763 ops/s # Warmup Iteration 11: 32834442.289 ops/s # Warmup Iteration 12: 34217782.915 ops/s # Warmup Iteration 13: 33036828.248 ops/s # Warmup Iteration 14: 34368855.165 ops/s # Warmup Iteration 15: 34415523.035 ops/s # Warmup Iteration 16: 31187588.079 ops/s # Warmup Iteration 17: 32594818.974 ops/s # Warmup Iteration 18: 34086802.016 ops/s # Warmup Iteration 19: 34340272.384 ops/s # Warmup Iteration 20: 28259357.798 ops/s Iteration 1: 31757196.070 ops/s Iteration 2: 33991747.455 ops/s Iteration 3: 34024018.852 ops/s Iteration 4: 33996716.542 ops/s Iteration 5: 29979159.027 ops/s Iteration 6: 34012243.975 ops/s Iteration 7: 33990813.479 ops/s Iteration 8: 34083707.765 ops/s Iteration 9: 34107629.820 ops/s Iteration 10: 27896785.113 ops/s Iteration 11: 30772172.806 ops/s Iteration 12: 33765139.270 ops/s Iteration 13: 34369680.171 ops/s Iteration 14: 34465158.746 ops/s Iteration 15: 28118201.187 ops/s Iteration 16: 30669149.170 ops/s Iteration 17: 32676396.546 ops/s Iteration 18: 34190840.882 ops/s Iteration 19: 34238377.372 ops/s Iteration 20: 27737131.008 ops/s # Run progress: 70.00% complete, ETA 00:08:38 # Fork: 8 of 10 # Warmup Iteration 1: 28630824.119 ops/s # Warmup Iteration 2: 33818762.541 ops/s # Warmup Iteration 3: 35038007.951 ops/s # Warmup Iteration 4: 36304928.826 ops/s # Warmup Iteration 5: 36354056.932 ops/s # Warmup Iteration 6: 37772679.687 ops/s # Warmup Iteration 7: 35227674.534 ops/s # Warmup Iteration 8: 38029506.671 ops/s # Warmup Iteration 9: 34585248.627 ops/s # Warmup Iteration 10: 37248219.973 ops/s # Warmup Iteration 11: 34593434.702 ops/s # Warmup Iteration 12: 35464181.287 ops/s # Warmup Iteration 13: 36696009.835 ops/s # Warmup Iteration 14: 38316197.354 ops/s # Warmup Iteration 15: 38266037.386 ops/s # Warmup Iteration 16: 37189662.171 ops/s # Warmup Iteration 17: 36523113.799 ops/s # Warmup Iteration 18: 37988022.876 ops/s # Warmup Iteration 19: 38051736.146 ops/s # Warmup Iteration 20: 31182088.185 ops/s Iteration 1: 37190441.731 ops/s Iteration 2: 37956882.826 ops/s Iteration 3: 38140733.603 ops/s Iteration 4: 37252516.227 ops/s Iteration 5: 31725393.553 ops/s Iteration 6: 36471814.199 ops/s Iteration 7: 38114054.355 ops/s Iteration 8: 32616409.003 ops/s Iteration 9: 37786024.918 ops/s Iteration 10: 37992346.638 ops/s Iteration 11: 38123237.062 ops/s Iteration 12: 38287723.965 ops/s Iteration 13: 38345880.203 ops/s Iteration 14: 31130022.209 ops/s Iteration 15: 37986966.666 ops/s Iteration 16: 36960266.429 ops/s Iteration 17: 38008103.179 ops/s Iteration 18: 38014088.784 ops/s Iteration 19: 38110627.648 ops/s Iteration 20: 38072572.537 ops/s # Run progress: 80.00% complete, ETA 00:05:39 # Fork: 9 of 10 # Warmup Iteration 1: 28298513.112 ops/s # Warmup Iteration 2: 32838632.035 ops/s # Warmup Iteration 3: 30181316.633 ops/s # Warmup Iteration 4: 32909381.568 ops/s # Warmup Iteration 5: 31944847.556 ops/s # Warmup Iteration 6: 33397277.722 ops/s # Warmup Iteration 7: 30750924.273 ops/s # Warmup Iteration 8: 33913172.836 ops/s # Warmup Iteration 9: 31744562.260 ops/s # Warmup Iteration 10: 33605243.253 ops/s # Warmup Iteration 11: 31510842.700 ops/s # Warmup Iteration 12: 33828656.623 ops/s # Warmup Iteration 13: 31525600.401 ops/s # Warmup Iteration 14: 34036366.024 ops/s # Warmup Iteration 15: 34031912.703 ops/s # Warmup Iteration 16: 29092574.272 ops/s # Warmup Iteration 17: 32539488.819 ops/s # Warmup Iteration 18: 32600231.822 ops/s # Warmup Iteration 19: 32928686.312 ops/s # Warmup Iteration 20: 33536586.546 ops/s Iteration 1: 30083475.241 ops/s Iteration 2: 32341395.220 ops/s Iteration 3: 33803703.325 ops/s Iteration 4: 33915545.687 ops/s Iteration 5: 30320419.165 ops/s Iteration 6: 33472727.881 ops/s Iteration 7: 33757353.957 ops/s Iteration 8: 28339704.610 ops/s Iteration 9: 33045545.359 ops/s Iteration 10: 33815271.934 ops/s Iteration 11: 33793968.698 ops/s Iteration 12: 33715714.353 ops/s Iteration 13: 33979632.042 ops/s Iteration 14: 29129416.976 ops/s Iteration 15: 32352103.774 ops/s Iteration 16: 32349089.070 ops/s Iteration 17: 32198286.479 ops/s Iteration 18: 29763083.673 ops/s Iteration 19: 30985401.866 ops/s Iteration 20: 30704515.609 ops/s # Run progress: 90.00% complete, ETA 00:02:45 # Fork: 10 of 10 # Warmup Iteration 1: 25845863.121 ops/s # Warmup Iteration 2: 33218974.229 ops/s # Warmup Iteration 3: 32576422.877 ops/s # Warmup Iteration 4: 33624698.333 ops/s # Warmup Iteration 5: 32881377.229 ops/s # Warmup Iteration 6: 33675931.296 ops/s # Warmup Iteration 7: 31678171.139 ops/s # Warmup Iteration 8: 31865457.116 ops/s # Warmup Iteration 9: 32035721.100 ops/s # Warmup Iteration 10: 33759626.899 ops/s # Warmup Iteration 11: 32020679.489 ops/s # Warmup Iteration 12: 33497805.239 ops/s # Warmup Iteration 13: 31818025.906 ops/s # Warmup Iteration 14: 34086770.330 ops/s # Warmup Iteration 15: 34168967.286 ops/s # Warmup Iteration 16: 28807710.513 ops/s # Warmup Iteration 17: 31152856.399 ops/s # Warmup Iteration 18: 33772983.915 ops/s # Warmup Iteration 19: 34020496.828 ops/s # Warmup Iteration 20: 28814678.720 ops/s Iteration 1: 31022028.693 ops/s Iteration 2: 33609915.911 ops/s Iteration 3: 32123372.543 ops/s Iteration 4: 27813625.332 ops/s Iteration 5: 31379592.611 ops/s Iteration 6: 32644747.339 ops/s Iteration 7: 33793411.987 ops/s Iteration 8: 30422277.460 ops/s Iteration 9: 32626659.385 ops/s Iteration 10: 33719480.304 ops/s Iteration 11: 33980011.600 ops/s Iteration 12: 28107750.520 ops/s Iteration 13: 31126083.092 ops/s Iteration 14: 32649007.164 ops/s Iteration 15: 33744248.267 ops/s Iteration 16: 34026461.866 ops/s Iteration 17: 27717690.095 ops/s Iteration 18: 31491088.409 ops/s Iteration 19: 32894429.409 ops/s Iteration 20: 33722538.163 ops/s Result "org.sample.ByteBufferBenchmark.benchmark_byte_buffer_put": 33100911.857 ±(99.9%) 747461.951 ops/s [Average] (min, avg, max) = (25373082.559, 33100911.857, 38885170.177), stdev = 3164800.705 CI (99.9%): [32353449.906, 33848373.808] (assumes normal distribution) # Run complete. Total time: 00:27:27 Benchmark Mode Cnt Score Error Units ByteBufferBenchmark.benchmark_byte_buffer_put thrpt 200 33100911.857 ± 747461.951 ops/s [9walsbp@dolphin ~]$ ./build_without/jdk/bin/java -jar benchmarks.jar WARNING: An illegal reflective access operation has occurred WARNING: Illegal reflective access by org.openjdk.jmh.util.Utils (file:/home/9walsbp/benchmarks.jar) to field java.io.Console.cs WARNING: Please consider reporting this to the maintainers of org.openjdk.jmh.util.Utils WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations WARNING: All illegal access operations will be denied in a future release # JMH version: 1.20 # VM version: JDK 10-internal, VM 10-internal+0-adhoc.walshbp.jdk # VM invoker: /home/9walsbp/build_without/jdk/bin/java # VM options: <none> # Warmup: 20 iterations, 1 s each # Measurement: 20 iterations, 1 s each # Timeout: 10 min per iteration # Threads: 1 thread, will synchronize iterations # Benchmark mode: Throughput, ops/time # Benchmark: org.sample.ByteBufferBenchmark.benchmark_byte_buffer_put # Run progress: 0.00% complete, ETA 00:06:40 # Fork: 1 of 10 # Warmup Iteration 1: 29113219.200 ops/s # Warmup Iteration 2: 38390854.347 ops/s # Warmup Iteration 3: 37576196.805 ops/s # Warmup Iteration 4: 38517882.972 ops/s # Warmup Iteration 5: 38838678.528 ops/s # Warmup Iteration 6: 38722019.753 ops/s # Warmup Iteration 7: 30279515.339 ops/s # Warmup Iteration 8: 37301591.985 ops/s # Warmup Iteration 9: 38937014.242 ops/s # Warmup Iteration 10: 38446665.693 ops/s # Warmup Iteration 11: 35988668.446 ops/s # Warmup Iteration 12: 37681609.419 ops/s # Warmup Iteration 13: 38993187.956 ops/s # Warmup Iteration 14: 37414379.929 ops/s # Warmup Iteration 15: 38753712.247 ops/s # Warmup Iteration 16: 38753551.189 ops/s # Warmup Iteration 17: 33767765.399 ops/s # Warmup Iteration 18: 37450537.087 ops/s # Warmup Iteration 19: 39118737.402 ops/s # Warmup Iteration 20: 39031101.838 ops/s Iteration 1: 32912027.168 ops/s Iteration 2: 37597695.079 ops/s Iteration 3: 37116802.899 ops/s Iteration 4: 37425452.741 ops/s Iteration 5: 31759009.838 ops/s Iteration 6: 37428294.033 ops/s Iteration 7: 38607838.742 ops/s Iteration 8: 34858025.193 ops/s Iteration 9: 36273653.347 ops/s Iteration 10: 38886985.073 ops/s Iteration 11: 38684265.699 ops/s Iteration 12: 30418949.886 ops/s Iteration 13: 36510488.388 ops/s Iteration 14: 37732064.835 ops/s Iteration 15: 37907332.810 ops/s Iteration 16: 38640267.003 ops/s Iteration 17: 31545863.662 ops/s Iteration 18: 36326351.514 ops/s Iteration 19: 37504107.281 ops/s Iteration 20: 36925861.540 ops/s # 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Run complete. Total time: 00:27:51 Benchmark Mode Cnt Score Error Units ByteBufferBenchmark.benchmark_byte_buffer_put thrpt 200 35604933.518 ± 654975.515 ops/s ... So a performance degradation of roughly 7%. Regards, Ben Walsh From: Paul Sandoz <paul.sandoz@oracle.com> To: Ben Walsh <ben_walsh@uk.ibm.com> Cc: core-libs-dev <core-libs-dev@openjdk.java.net> Date: 01/02/2018 22:50 Subject: Re: [PATCH] Reduce Chance Of Mistakenly Early Backing Memory Cleanup Hi Ben, I don?t think you require the fence in all the cases you have currently placed it e.g. here for example $memtype$ y = $toBits$(x); UNSAFE.put$Memtype$Unaligned(null, a, y, bigEndian); + Reference.reachabilityFence(this); return this; since ?this? is being returned it will be kept live during the unsafe access. Would you mind providing a JMH benchmark and results for the performance with and without the fence for say a put and/or a get. I would like to understand the performance impact on HotSpot, this is one reason why we have yet to add such fences as it will likely impact performance. At the moment we are relying on the method not being inlined, which is an expedient technique to make it functional and keep a reference alive but not necessarily optimal for usages in DBB. For more details see: https://bugs.openjdk.java.net/browse/JDK-8169605 https://bugs.openjdk.java.net/browse/JDK-8149610 Thanks, Paul. On Feb 1, 2018, at 6:55 AM, Ben Walsh <ben_walsh@uk.ibm.com> wrote: This contribution forms a partial solution to the problem detailed here - http://thevirtualmachinist.blogspot.ca/2011/07/subtle-issue-of-reachability.... . In this context, this contribution provides "markers" such that a suitably "aware" compiler can reduce the chances of such a problem occurring with each of the Direct<Type>Buffer<RW><BO> objects and MappedByteBuffer object. The reachabilityFences may prevent crashes / exceptions due to cleaning up the backing memory before the user has finished using the pointer. Any compiler not suitably "aware" could be modified to make use of the "markers". I would like to pair with a sponsor to contribute this patch ... ------------------------------------------------------------------------------------------------------------------- diff -r d51e64840b4f src/java.base/share/classes/java/nio/Direct-X-Buffer-bin.java.template --- a/src/java.base/share/classes/java/nio/Direct-X-Buffer-bin.java.template Wed Jan 31 12:04:53 2018 +0800 +++ b/src/java.base/share/classes/java/nio/Direct-X-Buffer-bin.java.template Thu Feb 01 11:30:10 2018 +0000 @@ -1,5 +1,5 @@ /* - * Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved. + * Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it @@ -33,15 +33,21 @@ private $type$ get$Type$(long a) { $memtype$ x = UNSAFE.get$Memtype$Unaligned(null, a, bigEndian); - return $fromBits$(x); + $type$ y = $fromBits$(x); + Reference.reachabilityFence(this); + return y; } public $type$ get$Type$() { - return get$Type$(ix(nextGetIndex($BYTES_PER_VALUE$))); + $type$ y = get$Type$(ix(nextGetIndex($BYTES_PER_VALUE$))); + Reference.reachabilityFence(this); + return y; } public $type$ get$Type$(int i) { - return get$Type$(ix(checkIndex(i, $BYTES_PER_VALUE$))); + $type$ y = get$Type$(ix(checkIndex(i, $BYTES_PER_VALUE$))); + Reference.reachabilityFence(this); + return y; } #end[rw] @@ -50,6 +56,7 @@ #if[rw] $memtype$ y = $toBits$(x); UNSAFE.put$Memtype$Unaligned(null, a, y, bigEndian); + Reference.reachabilityFence(this); return this; #else[rw] throw new ReadOnlyBufferException(); diff -r d51e64840b4f src/java.base/share/classes/java/nio/Direct-X-Buffer.java.template --- a/src/java.base/share/classes/java/nio/Direct-X-Buffer.java.template Wed Jan 31 12:04:53 2018 +0800 +++ b/src/java.base/share/classes/java/nio/Direct-X-Buffer.java.template Thu Feb 01 11:30:10 2018 +0000 @@ -1,5 +1,5 @@ /* - * Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved. + * Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it @@ -28,6 +28,7 @@ package java.nio; import java.io.FileDescriptor; +import java.lang.ref.Reference; import jdk.internal.misc.VM; import jdk.internal.ref.Cleaner; import sun.nio.ch.DirectBuffer; @@ -312,6 +313,7 @@ public $Type$Buffer put($type$ x) { #if[rw] UNSAFE.put$Swaptype$(ix(nextPutIndex()), $swap$($toBits$(x))); + Reference.reachabilityFence(this); return this; #else[rw] throw new ReadOnlyBufferException(); @@ -321,6 +323,7 @@ public $Type$Buffer put(int i, $type$ x) { #if[rw] UNSAFE.put$Swaptype$(ix(checkIndex(i)), $swap$($toBits$(x))); + Reference.reachabilityFence(this); return this; #else[rw] throw new ReadOnlyBufferException(); @@ -347,6 +350,7 @@ if (srem > rem) throw new BufferOverflowException(); UNSAFE.copyMemory(sb.ix(spos), ix(pos), (long)srem << $LG_BYTES_PER_VALUE$); + Reference.reachabilityFence(this); sb.position(spos + srem); position(pos + srem); } else if (src.hb != null) { @@ -413,6 +417,7 @@ int rem = (pos <= lim ? lim - pos : 0); UNSAFE.copyMemory(ix(pos), ix(0), (long)rem << $LG_BYTES_PER_VALUE$); + Reference.reachabilityFence(this); position(rem); limit(capacity()); discardMark(); @@ -505,6 +510,7 @@ void _put(int i, byte b) { // package-private #if[rw] UNSAFE.putByte(address + i, b); + Reference.reachabilityFence(this); #else[rw] throw new ReadOnlyBufferException(); #end[rw] diff -r d51e64840b4f src/java.base/share/classes/java/nio/MappedByteBuffer.java --- a/src/java.base/share/classes/java/nio/MappedByteBuffer.java Wed Jan 31 12:04:53 2018 +0800 +++ b/src/java.base/share/classes/java/nio/MappedByteBuffer.java Thu Feb 01 11:30:10 2018 +0000 @@ -1,5 +1,5 @@ /* - * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved. + * Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it @@ -26,6 +26,7 @@ package java.nio; import java.io.FileDescriptor; +import java.lang.ref.Reference; import jdk.internal.misc.Unsafe; @@ -164,6 +165,7 @@ // is computed as we go along to prevent the compiler from otherwise // considering the loop as dead code. Unsafe unsafe = Unsafe.getUnsafe(); + Reference.reachabilityFence(this); int ps = Bits.pageSize(); int count = Bits.pageCount(length); long a = mappingAddress(offset); ------------------------------------------------------------------------------------------------------------------- Regards, Ben Walsh Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU