RFR: 8350983: JShell LocalExecutionControl only needs stopCheck() on backward branches

[Chen Liang]

On Sat, 1 Mar 2025 03:14:20 GMT, Archie Cobbs <acobbs at openjdk.org> wrote:

> JShell's `LocalExecutionControl` ensures a running eval thread can be stopped by `JShell.stop()` by inserting an invocation of `stopCheck()` at every branch point in the bytecode of loaded classfiles.
> 
> However, this same guarantee can be provided by invoking `stopCheck()` only at backward branches and not at forward branches. By doing this, the performance and size impact on the executing code can be reduced.
> 
> Fortunately the new ClassFile API makes this kind of modification easy 👍

src/jdk.jshell/share/classes/jdk/jshell/execution/LocalExecutionControl.java line 102:

> 100:                                 return (cob, coe) -> {
> 101:                                     switch (coe) {
> 102:                                     case BranchInstruction branch:

Can we use switch with `->` instead of `:` to avoid the error-prone breaks?

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PR Review Comment: https://git.openjdk.org/jdk/pull/23850#discussion_r1976864784