How to get backtrace of `@async` Task

General Usage
2

You can either print the error yourself or look at what the task resolves to:

function start_async_print()
    start_time = time()
    t = @async try
        do_some_work(10)
    catch err
        bt = catch_backtrace()
        println()
        showerror(stderr, err, bt)
    end
    while !istaskdone(t)
        println("start() is waiting for do_some_work() to be done")
        sleep(1)
    end
end

function start_async_throw()
    start_time = time()
    t = do_some_work(10)
    while !istaskdone(t)
        println("start() is waiting for do_some_work() to be done")
        sleep(1)
    end
    wait(t) # or fetch(t)
end

gives

julia> start_async_print()
start() is waiting for do_some_work() to be done

UndefVarError: b not defined
Stacktrace:
 [1] do_some_work at ./untitled-8822451613b5304f5f50924dadde5d27:6 [inlined]
 [2] (::getfield(Main, Symbol("##27#28")))() at ./task.jl:259
julia> start_async_throw()
ERROR: UndefVarError: b not defined
Stacktrace:
 [1] do_some_work at ./untitled-8822451613b5304f5f50924dadde5d27:6 [inlined]
 [2] start_async_throw() at ./untitled-8822451613b5304f5f50924dadde5d27:33
 [3] top-level scope at none:0

The wait/fetch approach obviously doesn’t work very well when you don’t want to block.

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