Ktor performance improvements

Out of curiosity I’ve made small profiling session of ktor via FullBenchmark.kt, but added query string and its parsing (to emulate more realistic workload).

CPU profile: http://svgshare.com/i/4XN.svg Allocation profile: http://svgshare.com/i/4X_.svg (note that this one may be inaccurate due to profile method skew)

Observations:

1. Query string parsing is dominating CPU consumer. E.g. for comparison two OK methods, one without query string and one with medium-size one (~80 characters):

Benchmark                      Mode  Cnt  Score   Error  Units
FullBenchmark.sayOK            avgt   10  3.507 ± 0.062  us/op
FullBenchmark.sayOKLongParams  avgt   10  5.783 ± 1.286  us/op

It can be simply optimized (pre-size ValuesMap, don’t use lazy filtering sequences for splitting, etc.)

1. Most of lazy properties shouldn’t be thread-safe (SynchronizedLazyImpl -> UnsafeLazyImpl). It’s specific for TestApplicationRequest and TestApplicationResponse, but I’ve seen this in real request/response classes (e.g. in netty)

2. Headers, probably, shouldn’t be lazy at all neither in request nor in response, because they are always required and read.

3. Pipeline#merge is implemented in non-trivial (for me) way:

val interceptors = ArrayList<PipelineInterceptor<TSubject, TContext>>(fromContent.interceptors.size)
interceptors.fastAddAll(fromContent.interceptors)

where fastAddAll ensures capacity and adds element one by one, where each add ensures capacity on its own. Why is it better than

val interceptors = ArrayList<PipelineInterceptor<TSubject, TContext>>(fromContent.interceptors)

? It’s rather about code style, than performance though

1. ValuesMap#ensureListForKey (~15% of CPU) may be implemented via computeIfAbsent, though it’s should be measured first.

If you think these issues are valid I don’t mind to fix them

[orangy]

Thanks. Small note, benchmarks infra can do better:

    benchmark(args) {
        threads = 1
        iterations = 10000
        run<FullBenchmark>("sayOKLongParams")
    }

Instead of manually commenting annotations and modifying constants.

[qwwdfsad]

Thanks, I will close this issue. FYI this session revealed KT-22042