http://jvns.ca/blog/2016/06/12/a-weird-system-call-process-v...
I love the JVM's easily trace-ability, though that involves safepoints, so that's not completely out of process either.
Java stems from Sun. Sun made Solaris. And Solaris had an ideology about transparency and discoverability of running systems. They have some outright amazing tools for introspection into a binary that is running. This probably creates an environment in which the same would happen for the JVM. In fact, the `jstack` name seem very familiar to DTrace (and mdb(1)) users.
Days since I last solved a problem on the JVM through a heapDump: 2.
* "Python" in general might mean you're on Linux/Windows/whatever, and it might mean CPython, PyPy, or some other runtime. But any out-of-process instrumentation is gonna have to be pretty platform/runtime specific.
* Even if we restrict ourselves to, say, CPython on Linux, the interpreter's internals aren't super friendly to this sort of inspection from the outside. You have to rely on and also work around implementation details.
Example: to get a Python call stack, you want to look at `PyThreadState_Current` (basically the same idea as `ruby_current_thread` in that excellent linked post of Julia's, I think). But this happens to be null whenever the GIL is released, e.g. when doing network I/O, and then you're kind of out of luck. So you'll already have trouble usefully profiling a single-threaded I/O-intensive program.
* Oh and you pretty much need debug symbols in your CPython binary (I think? Tell me if this isn't true!). Most production CPython builds don't have them. So you have to get the right binary, and rebuild any application dependencies with C extensions. Not hard but annoying.
There is potential though! With some work, we definitely could have a better story for out-of-process Python profiling a la Linux perf.
If it follows standard System Linkage, its easy to point gdb or any other system debugger or profiler to debug and profile the application.
Some runtimes have a mix of System and Private linkage, ie C functions will follow System Linkage but JIT'ed code frames might follow private linkage. This makes for difficult stack-walking by system native debuggers and profilers. You'd have to teach GDB via an extension how to walk the non-standard frames.
So yea, long story short, it depends on the linkage convention the implementers of the language runtime decided to follow.