Avoid String.split when parsing header to reduce some garbage generat…

[anuraaga]

…ion.

Description of changes:

Instead of String.split, can use indexOf to reduce allocations of arrays. About 20% faster / less allocations, not huge but these things add up and as instrumentation we need to keep an eye on minimizing cycles to reduce the cost burden of the customer. I would say the readability is not significantly impaired. @shengxil feel free to copy this away.

After

Benchmark                                                      Mode     Cnt     Score    Error   Units
TraceHeaderBenchmark.parse                                   sample  437664     2.024 ±  0.209   us/op
TraceHeaderBenchmark.parse:parse·p0.00                       sample             0.498            us/op
TraceHeaderBenchmark.parse:parse·p0.50                       sample             0.800            us/op
TraceHeaderBenchmark.parse:parse·p0.90                       sample             0.934            us/op
TraceHeaderBenchmark.parse:parse·p0.95                       sample             1.170            us/op
TraceHeaderBenchmark.parse:parse·p0.99                       sample             4.496            us/op
TraceHeaderBenchmark.parse:parse·p0.999                      sample            40.021            us/op
TraceHeaderBenchmark.parse:parse·p0.9999                     sample          1761.280            us/op
TraceHeaderBenchmark.parse:parse·p1.00                       sample          3551.232            us/op
TraceHeaderBenchmark.parse:·gc.alloc.rate                    sample      15   627.784 ± 53.949  MB/sec
TraceHeaderBenchmark.parse:·gc.alloc.rate.norm               sample      15  1072.556 ±  0.061    B/op
TraceHeaderBenchmark.parse:·gc.churn.G1_Eden_Space           sample      15   631.644 ± 86.257  MB/sec
TraceHeaderBenchmark.parse:·gc.churn.G1_Eden_Space.norm      sample      15  1076.679 ± 92.875    B/op
TraceHeaderBenchmark.parse:·gc.churn.G1_Survivor_Space       sample      15     0.100 ±  0.017  MB/sec
TraceHeaderBenchmark.parse:·gc.churn.G1_Survivor_Space.norm  sample      15     0.172 ±  0.030    B/op
TraceHeaderBenchmark.parse:·gc.count                         sample      15    94.000           counts
TraceHeaderBenchmark.parse:·gc.time                          sample      15    95.000               ms

Before

Benchmark                                                      Mode     Cnt     Score     Error   Units
TraceHeaderBenchmark.parse                                   sample  372019     2.519 ±   0.257   us/op
TraceHeaderBenchmark.parse:parse·p0.00                       sample             0.609             us/op
TraceHeaderBenchmark.parse:parse·p0.50                       sample             0.939             us/op
TraceHeaderBenchmark.parse:parse·p0.90                       sample             1.102             us/op
TraceHeaderBenchmark.parse:parse·p0.95                       sample             1.552             us/op
TraceHeaderBenchmark.parse:parse·p0.99                       sample            15.680             us/op
TraceHeaderBenchmark.parse:parse·p0.999                      sample            60.283             us/op
TraceHeaderBenchmark.parse:parse·p0.9999                     sample          2006.213             us/op
TraceHeaderBenchmark.parse:parse·p1.00                       sample          3317.760             us/op
TraceHeaderBenchmark.parse:·gc.alloc.rate                    sample      15   719.021 ±  36.796  MB/sec
TraceHeaderBenchmark.parse:·gc.alloc.rate.norm               sample      15  1448.702 ±   0.038    B/op
TraceHeaderBenchmark.parse:·gc.churn.G1_Eden_Space           sample      15   726.083 ±  72.496  MB/sec
TraceHeaderBenchmark.parse:·gc.churn.G1_Eden_Space.norm      sample      15  1461.632 ± 107.197    B/op
TraceHeaderBenchmark.parse:·gc.churn.G1_Survivor_Space       sample      15     0.082 ±   0.084  MB/sec
TraceHeaderBenchmark.parse:·gc.churn.G1_Survivor_Space.norm  sample      15     0.165 ±   0.168    B/op
TraceHeaderBenchmark.parse:·gc.count                         sample      15   108.000            counts
TraceHeaderBenchmark.parse:·gc.time                          sample      15   109.000                ms

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[willarmiros]

Looks like a great speedup and simplification. Thanks!