Thread-safety of concurrent GetParser().Parse() with single shared env

[t12g]

Hi,
This is another thread safe question similar to #878.

We are using CEL in Python. We share a single process-wide cel.NewEnv(), built once (no runtime variable/function/extension registration), to evaluate user-authored filters. We only call compile(..., disable_check=True), which in the wrapper takes the compiler->GetParser().Parse(...) path. We make concurrent calls on GetParser().Parse() from multiple threads on the same Compiler. "Compiler instances should be thread-compatible" is documented on the Compiler, but we couldn’t find thread-safety comments on Parser. Based on the code, it appears that it is safe to have concurrent GetParser().Parse() calls, but want to double-check here in case we read it wrong.

tagging @TristonianJones here since he answered the previous thread-safety question

[TristonianJones]

Hi @t12g, the CEL Python stack is built in C++, so it should be thread compatible unless we've done something silly in the Python wrappers