Todays implementation looks at each char in a string, and appends that to a StringBuilder according to certain rules. This is needed in order to handle unicode and escaped characters.

This leaves room for an optimization if we observe that most strings we write will be unescaped and within ascii range.

See 163-cpu-flamegraph-2021-03-12-12-47-10.svg for evidence of this

Approach:

Split write-string in a fast path and a slow path. As long as we only see unescaped ascii chars, we stay on the fast path and write the string directly to the PrintWriter. As soon as we see anything else, we use the old implementation of write-string to deal with it.

Benchmark:

This is based applying the patch from

See 183-cpu-flamegraph-2021-03-12-13-21-48.svg for flame graph after patch applied

Patch:

0001-DJSON-34-Speed-up-writing-strings.patch

Approach 2 Consolidate String writing

Don’t split the string writing. This also solves

Benchmark:

Patch:

0002-DJSON-34-Speed-up-writing-strings.patch