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perf: use unsynchronized StringBuilderWriter in std.deepJoin #889

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Merged
stephenamar-db merged 1 commit into from
Jun 3, 2026
Merged

perf: use unsynchronized StringBuilderWriter in std.deepJoin #889

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5 changes: 4 additions & 1 deletion sjsonnet/src/sjsonnet/stdlib/ManifestModule.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -337,7 +337,10 @@ object ManifestModule extends AbstractFunctionModule {
*/
private object DeepJoin extends Val.Builtin1("deepJoin", "arr") {
def evalRhs(value: Eval, ev: EvalScope, pos: Position): Val = {
val out = new StringWriter()
// Use the unsynchronized StringBuilderWriter: each Val.Str chunk triggers
// out.write(...) in a tight loop, and StringWriter's backing StringBuffer
// pays a monitor enter/exit per call. Same swap pattern as TomlRenderer (#875).
val out = new StringBuilderWriter()
val q = new java.util.ArrayDeque[Eval]()
q.add(value)
while (!q.isEmpty) {
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