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 invocing 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 👍