What does a failure on a thread do when nobody is waiting for it?

Level: 201 · anyone whose worker thread died quietly

Stub — a question and its expected answers, not yet a lesson. No program behind this page has been written or run, so nothing on it has been through the check that backs every finished page. The table is what the finished lesson is expected to find, and every cell is unverified until a program prints it. (Not machine-checked here.)

One line: A panic, an exception or a crash on a thread that nobody joins is either a program-wide failure or a silent one, and the six languages split down the middle: Go ends the process, Rust and Java keep it running with the thread's failure printed to stderr, C++ calls std::terminate, C dies only if the failure is a signal, and Python prints a traceback and carries on.

The question

Getting a result back shows a thread's failure travelling through its join. This page removes the join. A thread panics, throws or segfaults, and no handle is ever waited on: what happens to the rest of the program, what is printed, and what is the exit status? The answer decides whether a worker that dies at three in the morning takes the server with it or leaves it running with one worker fewer and nothing in the log.

What each language is expected to say

	Expected answer, to be verified by the program
Rust	the panic is printed to stderr with the thread's name; the process continues and exits 0 unless main itself panics
Go	any unrecovered panic on any goroutine ends the whole process, exit status 2, with the goroutine's stack
C	no failure mechanism except a signal: a SIGSEGV on any thread kills the process, exit 139
C++	an exception leaving a std::thread function calls std::terminate, exit by SIGABRT
Java	the uncaught exception is printed by the default handler; the process continues, exit 0
Python	the traceback is printed by threading.excepthook; the process continues, exit 0

What the programs have to show

• one program per language: a thread that fails deliberately, a main that sleeps two seconds and then prints and exits 0
• a .sh driver per language keeping the last line printed, whether main's line appeared, and the exit status
• the Rust and Java rows with a main that later joins the handle, to show the failure is not lost, only deferred

See also

• After this: How many threads can you start?
• Getting a result back
• Who waits when main returns?
• The Go library's A panic ends the whole program ↗
• The Rust library's Spawning a thread ↗
• Concepts: Safety failure · Liveness failure · Join · Daemon and detached threads