test/channels.jl - master - githubmirror/julia

test/channels.jl
789 строк23 KB
Andy Dienes
wait-after-close no longer errors on one-shot Timers (#62539)
06 авг 2026, 01:12
06 авг 2026, 01:12e9cc45c
# This file is a part of Julia. License is MIT: https://julialang.org/license

using Random
using Base.Threads
using Base: Experimental
using Base: n_avail

@testset "single-threaded Condition usage" begin
    a = Condition()
    t = @async begin
        Base.notify(a, "success")
        "finished"
    end
    @test wait(a) == "success"
    @test fetch(t) == "finished"

    # Test printing
    @test repr(a) == "Condition()"
end

@testset "wait first behavior of wait on Condition" begin
    a = Condition()
    waiter1 = @async begin
        wait(a)
    end
    waiter2 = @async begin
        wait(a)
    end
    waiter3 = @async begin
        wait(a; first=true)
    end
    waiter4 = @async begin
        wait(a)
    end
    t = @async begin
        Base.notify(a, "success"; all=false)
        "finished"
    end
    @test fetch(waiter3) == "success"
    @test fetch(t) == "finished"
end

@testset "wait_with_timeout on Condition" begin
    a = Threads.Condition()
    @test @lock a Experimental.wait_with_timeout(a; timeout=0.1)==:timed_out
    lock(a)
    @spawn begin
        @lock a notify(a)
    end
    @test try
        Experimental.wait_with_timeout(a; timeout=2)
        true
    finally
        unlock(a)
    end
end

@testset "various constructors" begin
    c = Channel()
    @test eltype(c) == Any
    @test c.sz_max == 0
    @test isempty(c) == true  # Nothing in it
    @test isfull(c) == true   # But no more room

    c = Channel(1)
    @test eltype(c) == Any
    @test put!(c, 1) == 1
    @test isready(c) == true
    @test take!(c) == 1
    @test isready(c) == false
    @test eltype(Channel(1.0)) == Any

    c = Channel(1)
    @test isfull(c) == false
    put!(c, 1)
    @test isfull(c) == true

    c = Channel{Int}(1)
    @test eltype(c) == Int
    @test_throws MethodError put!(c, "Hello")

    c = Channel{Int}()
    @test eltype(c) == Int
    @test c.sz_max == 0

    c = Channel{Int}(Inf)
    @test eltype(c) == Int
    pvals = map(i->put!(c,i), 1:10^6)
    tvals = Int[take!(c) for i in 1:10^6]
    @test pvals == tvals

    @test_throws ArgumentError Channel(-1)
    @test_throws InexactError Channel(1.5)
end

@testset "Task constructors" begin
    c = Channel{Int}() do c; map(i->put!(c,i), 1:100); end
    @test eltype(c) == Int
    @test c.sz_max == 0
    @test collect(c) == 1:100

    c = Channel() do c; put!(c, 1); put!(c, "hi") end
    @test c.sz_max == 0
    @test collect(c) == [1, "hi"]

    c = Channel(Inf) do c; put!(c,1); end
    @test eltype(c) == Any
    @test c.sz_max == typemax(Int)
    c = Channel{Int}(Inf) do c; put!(c,1); end
    @test eltype(c) == Int
    @test c.sz_max == typemax(Int)

    taskref = Ref{Task}()
    c = Channel{Int}(0, taskref=taskref) do c; put!(c, 0); end
    @test eltype(c) == Int
    @test c.sz_max == 0
    @test istaskstarted(taskref[])
    @test !istaskdone(taskref[])
    take!(c); wait(taskref[])
    @test istaskdone(taskref[])

    # Legacy constructor
    c = Channel(ctype=Float32, csize=2) do c; map(i->put!(c,i), 1:100); end
    @test eltype(c) == Float32
    @test c.sz_max == 2
    @test isopen(c)
    @test collect(c) == 1:100
end
@testset "Multithreaded task constructors" begin
    taskref = Ref{Task}()
    c = Channel(spawn=true, taskref=taskref) do c; put!(c, 0); end
    # Test that the task is using the multithreaded scheduler
    @test taskref[].sticky == false
    @test collect(c) == [0]
end
let cmd = `$(Base.julia_cmd()) --depwarn=error --rr-detach --startup-file=no channel_threadpool.jl`
    new_env = copy(ENV)
    new_env["JULIA_NUM_THREADS"] = "1,1"
    run(pipeline(setenv(cmd, new_env), stdout = stdout, stderr = stderr))
end

@testset "multiple concurrent put!/take! on a channel for different sizes" begin
    function testcpt(sz)
        c = Channel{Int}(sz)
        size = 0
        inc() = size += 1
        dec() = size -= 1
        @sync for i = 1:10^4
            @async (sleep(rand()); put!(c, i); inc())
            @async (sleep(rand()); take!(c); dec())
        end
        @test size == 0
    end
    testcpt(0)
    testcpt(1)
    testcpt(32)
    testcpt(Inf)
end

@testset "type conversion in put!" begin
    c = Channel{Int64}(0)
    @async put!(c, Int32(1))
    wait(c)
    @test isa(take!(c), Int64)
    @test_throws MethodError put!(c, "")
    @assert !islocked(c.cond_take)
end

@testset "multiple for loops waiting on the same channel" begin
    # Test multiple "for" loops waiting on the same channel which
    # is closed after adding a few elements.
    c = Channel(32)
    results = []
    @sync begin
        for i in 1:20
            @async for ii in c
                push!(results, ii)
            end
        end
        sleep(1.0)
        for i in 1:5
            put!(c,i)
        end
        close(c)
    end
    @test sum(results) == 15
end

# Tests for channels bound to tasks.
using Distributed
@testset "channels bound to tasks" for N in [0, 10]
    # Normal exit of task
    c = Channel(N)
    bind(c, @async (GC.gc(); yield(); nothing))
    @test_throws InvalidStateException take!(c)
    @test !isopen(c)

    # Error exception in task
    c = Channel(N)
    task = @async (GC.gc(); yield(); error("foo"))
    bind(c, task)
    @test_throws TaskFailedException(task) take!(c)
    @test !isopen(c)

    # Multiple channels closed by the same bound task
    cs = [Channel(N) for i in 1:5]
    tf2() = begin
        GC.gc()
        if N > 0
            foreach(c -> (@assert take!(c) === 2), cs)
        end
        yield()
        error("foo")
    end
    task = Task(tf2)
    foreach(c -> bind(c, task), cs)
    schedule(task)

    if N > 0
        for i in 1:5
            @test put!(cs[i], 2) === 2
        end
    end
    for i in 1:5
        while isopen(cs[i])
            yield()
        end
        @test_throws TaskFailedException(task) wait(cs[i])
        @test_throws TaskFailedException(task) take!(cs[i])
        @test_throws TaskFailedException(task) put!(cs[i], 1)
        N == 0 || @test_throws TaskFailedException(task) fetch(cs[i])
        N == 0 && @test_throws ErrorException fetch(cs[i])
    end

    # Multiple tasks, first one to terminate closes the channel
    nth = rand(1:5)
    ref = Ref(0)
    tf3(i) = begin
        GC.gc()
        if i == nth
            ref[] = i
        else
            sleep(2.0)
        end
    end

    tasks = [Task(() -> tf3(i)) for i in 1:5]
    c = Channel(N)
    foreach(t -> bind(c, t), tasks)
    foreach(schedule, tasks)
    @test_throws InvalidStateException wait(c)
    @test !isopen(c)
    @test ref[] == nth
    @assert !islocked(c.cond_take)

    # channeled_tasks
    for T in [Any, Int]
        tf_chnls1 = (c1, c2) -> (@assert take!(c1) == 1; put!(c2, 2))
        chnls, tasks = Base.channeled_tasks(2, tf_chnls1; ctypes=[T,T], csizes=[N,N])
        put!(chnls[1], 1)
        @test take!(chnls[2]) === 2
        @test_throws InvalidStateException wait(chnls[1])
        @test_throws InvalidStateException wait(chnls[2])
        @test istaskdone(tasks[1])
        @test !isopen(chnls[1])
        @test !isopen(chnls[2])

        f = Future()
        tf4 = (c1, c2) -> begin
            @assert take!(c1) === 1
            wait(f)
        end

        tf5 = (c1, c2) -> begin
            put!(c2, 2)
            wait(f)
        end

        chnls, tasks = Base.channeled_tasks(2, tf4, tf5; ctypes=[T,T], csizes=[N,N])
        put!(chnls[1], 1)
        @test take!(chnls[2]) === 2
        yield()
        put!(f, 1) # allow tf4 and tf5 to exit after now, eventually closing the channel

        @test_throws InvalidStateException wait(chnls[1])
        @test_throws InvalidStateException wait(chnls[2])
        @test istaskdone(tasks[1])
        @test istaskdone(tasks[2])
        @test !isopen(chnls[1])
        @test !isopen(chnls[2])
    end

    # channel
    tf6 = c -> begin
        @assert take!(c) === 2
        error("foo")
    end

    for T in [Any, Int]
        taskref = Ref{Task}()
        chnl = Channel{T}(tf6, N, taskref=taskref)
        put!(chnl, 2)
        yield()
        @test_throws TaskFailedException(taskref[]) wait(chnl)
        @test istaskdone(taskref[])
        @test !isopen(chnl)
        @test_throws TaskFailedException(taskref[]) take!(chnl)
    end
end

@testset "timedwait" begin
    alwaystrue() = true
    alwaysfalse() = false
    @test timedwait(alwaystrue, 0) === :ok
    @test timedwait(alwaysfalse, 0) === :timed_out
    @test_throws ArgumentError timedwait(alwaystrue, 0; pollint=0)

    # Allowing a smaller positive `pollint` results in `timedwait` hanging
    @test_throws ArgumentError timedwait(alwaystrue, 0, pollint=1e-4)

    # Callback passed in raises an exception
    failure_cb = function (fail_on_call=1)
        i = 0
        function ()
            i += 1
            i >= fail_on_call && error("callback failed")
            return false
        end
    end

    @test_throws ErrorException("callback failed") timedwait(failure_cb(1), 0)
    @test_throws ErrorException("callback failed") timedwait(failure_cb(2), 0)

    # Validate that `timedwait` actually waits. Ideally we should also test that `timedwait`
    # doesn't exceed a maximum duration but that would require guarantees from the OS.
    duration = @elapsed timedwait(alwaysfalse, 1)  # Using default pollint of 0.1
    @test duration >= 1

    duration = @elapsed timedwait(alwaysfalse, 0; pollint=1)
    @test duration >= 1
end

@testset "timedwait on multiple channels" begin
    Experimental.@sync begin
        sync = Channel(1)
        rr1 = Channel(1)
        rr2 = Channel(1)
        rr3 = Channel(1)

        callback() = all(map(isready, [rr1, rr2, rr3]))
        # precompile functions which will be tested for execution time
        @test !callback()
        @test timedwait(callback, 0) === :timed_out

        @async begin put!(sync, :ready); sleep(0.5); put!(rr1, :ok) end
        @async begin sleep(1.0); put!(rr2, :ok) end
        @async begin @test take!(rr3) == :done end

        @test take!(sync) == :ready
        et = @elapsed timedwait(callback, 1)

        @test et >= 1.0

        @test isready(rr1)
        put!(rr3, :done)
    end
end

@testset "yield/wait/event failures" begin
    # garbage_finalizer returns `nothing` rather than the garbage object so
    # that the interpreter doesn't accidentally root the garbage when
    # interpreting the calling function.
    @noinline garbage_finalizer(f) = (finalizer(f, "gar" * "bage"); nothing)
    run = Ref(0)
    garbage_finalizer(Returns(nothing)) # warmup
    @test GC.enable(false)
    # test for finalizers trying to yield leading to failed attempts to context switch
    garbage_finalizer((x) -> (run[] += 1; sleep(1)))
    garbage_finalizer((x) -> (run[] += 1; yield()))
    garbage_finalizer((x) -> (run[] += 1; yieldto(@task () -> ())))
    t = @task begin
        @test !GC.enable(true)
        GC.gc()
        true
    end
    oldstderr = stderr
    newstderr = redirect_stderr()
    local errstream
    try
        errstream = @async read(newstderr[1], String)
        yield(t)
    finally
        redirect_stderr(oldstderr)
        close(newstderr[2])
    end
    @test istaskdone(t)
    @test fetch(t)
    @test run[] == 3
    output = fetch(errstream)
    @test 3 == length(findall(
        """error in running finalizer: ErrorException("task switch not allowed from inside gc finalizer")""", output))
    # test for invalid state in Workqueue during yield
    t = @async nothing
    @atomic t._state = 66
    newstderr = redirect_stderr()
    try
        errstream = @async read(newstderr[1], String)
        yield()
    finally
        redirect_stderr(oldstderr)
        close(newstderr[2])
    end
    @test fetch(errstream) == "\nWARNING: Workqueue inconsistency detected: popfirst!(Workqueue).state !== :runnable\n"
end

@testset "throwto" begin
    t = @task(nothing)
    ct = current_task()
    testerr = ErrorException("expected")
    @async Base.throwto(t, testerr)
    @test (try
        Base.wait(t)
        false
    catch ex
        ex
    end).task.exception === testerr
end

@testset "Timer / AsyncCondition triggering and race #12719" begin
    let tc = Ref(0)
        t = Timer(0) do t
            tc[] += 1
        end
        cb = first(t.cond.waitq).task::Task
        Libc.systemsleep(0.005)
        @test isopen(t)
        Base.process_events()
        @test !isopen(t)
        @test tc[] == 0
        yield()
        @test tc[] == 1
        @test istaskdone(cb)
    end

    let tc = Ref(0)
        t = Timer(0) do t
            tc[] += 1
        end
        cb = first(t.cond.waitq).task::Task
        Libc.systemsleep(0.005)
        @test isopen(t)
        close(t)
        @test !isopen(t)
        wait(cb)
        @test tc[] == 0
        @test t.handle === C_NULL
    end

    let tc = Ref(0)
        async = Base.AsyncCondition() do async
            tc[] += 1
        end
        cb = first(async.cond.waitq).task::Task
        @test isopen(async)
        ccall(:uv_async_send, Cvoid, (Ptr{Cvoid},), async)
        Base.process_events() # schedule event
        Sys.iswindows() && Base.process_events() # schedule event (windows?)
        ccall(:uv_async_send, Cvoid, (Ptr{Cvoid},), async)
        @test tc[] == 0
        yield() # consume event
        @test tc[] == 1
        ccall(:uv_async_send, Cvoid, (Ptr{Cvoid},), async)
        Base.process_events()
        Sys.iswindows() && Base.process_events() # schedule event (windows?)
        yield() # consume event
        @test tc[] == 2
        sleep(0.1) # no further events
        @test tc[] == 2
        ccall(:uv_async_send, Cvoid, (Ptr{Cvoid},), async)
        ccall(:uv_async_send, Cvoid, (Ptr{Cvoid},), async)
        Base.process_events() # schedule event
        Sys.iswindows() && Base.process_events() # schedule event (windows?)
        close(async) # and close
        @test !isopen(async)
        @test tc[] == 3
        @test tc[] == 3
        yield() # consume event & then close
        @test tc[] == 3
        sleep(0.1) # no further events
        wait(cb)
        @test tc[] == 3
        @test async.handle === C_NULL
    end

    let tc = Ref(0)
        async = Base.AsyncCondition() do async
            tc[] += 1
        end
        cb = first(async.cond.waitq).task::Task
        @test isopen(async)
        ccall(:uv_async_send, Cvoid, (Ptr{Cvoid},), async)
        Base.process_events() # schedule event
        Sys.iswindows() && Base.process_events() # schedule event (windows)
        close(async)
        @test !isopen(async)
        Base.process_events() # and close
        @test tc[] == 1
        yield() # consume event & then close
        @test tc[] == 1
        sleep(0.1) # no further events
        wait(cb)
        @test tc[] == 1
        @test async.handle === C_NULL
    end
end

struct CustomError <: Exception end

@testset "check_channel_state" begin
    c = Channel(1)
    close(c)
    @test !isopen(c)
    c.excp === nothing # to trigger the branch
    @test_throws InvalidStateException Base.check_channel_state(c)

    # Issue 52974 - closed channels with exceptions
    # must be thrown on iteration, if channel is empty
    c = Channel(2)
    put!(c, 5)
    close(c, CustomError())
    @test take!(c) == 5
    @test_throws CustomError iterate(c)

    c = Channel(Inf)
    put!(c, 1)
    close(c)
    @test take!(c) == 1
    @test_throws InvalidStateException take!(c)
    @test_throws InvalidStateException put!(c, 5)

    c = Channel(3)
    put!(c, 1)
    close(c)
    @test first(iterate(c)) == 1
    @test isnothing(iterate(c))
end

# PR #36641
# Ensure that `isempty()` does not mutate a Channel's state:
@testset "isempty(::Channel) mutation" begin
    function isempty_timeout(c::Channel)
        inner_c = Channel{Union{Bool,Nothing}}()
        @async put!(inner_c, isempty(c))
        @async begin
            sleep(0.01)
            if isopen(inner_c)
                put!(inner_c, nothing)
            end
        end
        result = take!(inner_c)
        if result === nothing
            error("isempty() timed out!")
        end
        return result
    end
    # First, with a non-buffered channel
    c = Channel()
    @test isempty_timeout(c)
    t_put = @async put!(c, 1)
    @test !isempty_timeout(c)
    # check a second time to ensure `isempty(c)` didn't just consume the element.
    @test !isempty_timeout(c)
    @test take!(c) == 1
    @test isempty_timeout(c)
    wait(t_put)

    # Next, with a buffered channel:
    c = Channel(2)
    @test isempty_timeout(c)
    t_put = put!(c, 1)
    @test !isempty_timeout(c)
    @test !isempty_timeout(c)
    @test take!(c) == 1
    @test isempty_timeout(c)
end

# issue #12473
# make sure 1-shot timers work
let a = []
    Timer(t -> push!(a, 1), 0.01, interval = 0)
    @test timedwait(() -> a == [1], 10) === :ok
end
let a = []
    Timer(t -> push!(a, 1), 0.01, interval = 0, spawn = true)
    @test timedwait(() -> a == [1], 10) === :ok
end

@testset "wait after closing a one-shot Timer (#34366)" begin
    t = Timer(600)
    close(t) # test assumes that thread won't get preempted for 10 minutes...
    @test_throws EOFError wait(t)

    t = Timer(0)
    @test wait(t) === nothing
    @test wait(t) === nothing
    close(t)
    @test wait(t) === nothing

    waiters = [Threads.@spawn wait(t) for _ in 1:8]
    @test all(w -> fetch(w) === nothing, waiters)

    for i in 1:100
        t = Timer(isodd(i) ? 0 : 0.001)
        racers = [Threads.@spawn begin
                for _ in 1:rand(0:8)
                    yield()
                end
                try
                    wait(t)
                    wait(t)
                    true
                catch e
                    e isa EOFError || rethrow()
                    false
                end
            end for _ in 1:4]
        for _ in 1:rand(0:8)
            yield()
        end
        close(t)
        outcomes = map(fetch, racers)
        @test all(outcomes) || !any(outcomes)
    end

    t = Timer(0, interval=600)
    @test wait(t) === nothing
    waiter = @task wait(t)
    yield(waiter)
    @test timedwait(() -> !isempty(t.cond.waitq) && first(t.cond.waitq).task === waiter, 10) === :ok
    close(t)
    @test_throws TaskFailedException wait(waiter)
    @test waiter.result isa EOFError
end

# make sure that we don't accidentally create a one-shot timer
let
    t = Timer(Returns(nothing), 10, interval=0.00001)
    @test ccall(:uv_timer_get_repeat, UInt64, (Ptr{Cvoid},), t) == 1
    close(t)
end

# make sure repeating timers work
@noinline function make_unrooted_timer(a)
    t = Timer(0.0, interval = 0.1)
    finalizer(t -> a[] += 1, t)
    wait(t)
    e = @elapsed for i = 1:5
        wait(t)
    end
    @test e >= 0.4
    @test a[] == 0
    nothing
end
let a = Ref(0)
    make_unrooted_timer(a)
    GC.gc()
    @test a[] == 1
end

@testset "Timer properties" begin
    t = Timer(1.0, interval = 0.5)
    @test t.timeout == 1.0
    @test t.interval == 0.5
    close(t)
    @test !isopen(t)
    @test t.timeout == 1.0
    @test t.interval == 0.5
end

# trying to `schedule` a finished task
let t = @async nothing
    wait(t)
    @test_throws ErrorException("schedule: Task not runnable") schedule(t, nothing)
end

@testset "push!(c, v) -> c" begin
    c = Channel(Inf)
    @test push!(c, nothing) === c
end

# Channel `show`
let c = Channel(3)
    @test repr(c) == "Channel{Any}(3)"
    @test repr(MIME("text/plain"), c) == "Channel{Any}(3) (empty)"
    put!(c, 0)
    @test repr(MIME("text/plain"), c) == "Channel{Any}(3) (1 item available)"
    put!(c, 1)
    @test repr(MIME("text/plain"), c) == "Channel{Any}(3) (2 items available)"
    close(c)
    @test repr(MIME("text/plain"), c) == "Channel{Any}(3) (closed)"
end

# PR #41833: data races in Channel
@testset "n_avail(::Channel)" begin
    # Buffered: n_avail() = buffer length + number of waiting tasks
    let c = Channel(2)
        @test n_avail(c) == 0;   put!(c, 0)
        @test n_avail(c) == 1;   put!(c, 0)
        @test n_avail(c) == 2;   t1 = @task put!(c, 0); yield(t1)
        @test n_avail(c) == 3;   t2 = @task put!(c, 0); yield(t2)
        @test n_avail(c) == 4
        # Test n_avail(c) after interrupting a task waiting on the channel
                                t3 = @task put!(c, 0)
                                yield(t3)
        @test n_avail(c) == 5
                                @async Base.throwto(t3, ErrorException("Exit put!"))
                                try wait(t3) catch end
        @test n_avail(c) == 4
                                close(c)
                                try wait(t1) catch end
                                try wait(t2) catch end
        @test n_avail(c) == 2    # Already-buffered items remain
    end
    # Unbuffered: n_avail() = number of waiting tasks
    let c = Channel()
        @test n_avail(c) == 0;   t1 = @task put!(c, 0); yield(t1)
        @test n_avail(c) == 1;   t2 = @task put!(c, 0); yield(t2)
        @test n_avail(c) == 2
        # Test n_avail(c) after interrupting a task waiting on the channel
                                t3 = @task put!(c, 0)
                                yield(t3)
        @test n_avail(c) == 3
                                @async Base.throwto(t3, ErrorException("Exit put!"))
                                try wait(t3) catch end
        @test n_avail(c) == 2
                                close(c)
                                try wait(t1) catch end
                                try wait(t2) catch end
        @test n_avail(c) == 0
    end
end

@testset "Task properties" begin
    f() = rand(2,2)
    t = Task(f)
    message = "Querying a Task's `scope` field is disallowed.\nThe private `Core.current_scope()` function is better, though still an implementation detail."
    @test_throws ErrorException(message) t.scope
    message = "Querying a Task's `invoked` field is disallowed because it is an implementation detail."
    @test_throws ErrorException(message) t.invoked
    message = "Setting a Task's `invoked` field directly is disallowed because it is an implementation detail."
    @test_throws ErrorException(message) (t.invoked = nothing)
    message = "Setting a Task's `result` field directly is disallowed. The result of a task is determined by the return value of its code; to pass a value to a suspended task, use `schedule(t, val)` or `yieldto(t, val)` instead."
    @test_throws ErrorException(message) (t.result = 42)
    @test t.state == :runnable
end

function _task(@nospecialize(f), stack::Int, @nospecialize(invoke))
    t = Core._task(f, stack, invoke)
    t.donenotify = Base.ThreadSynchronizer()
    return t
end
@testset "Core._task with invoke arguments" begin
    # Test _task with invoke Type argument
    f1() = 43
    f1(x...) = x
    t1 = _task(f1, 0, Tuple{})
    @test fetch(schedule(t1)) === 43
    t1 = _task(f1, 0, Tuple{Vararg})
    @test fetch(schedule(t1)) === ()
    t1 = _task(f1, 0, Tuple{typeof(f1)})
    schedule(t1)
    @test_throws TaskFailedException fetch(t1)

    # Test _task with Method argument
    m = which(f1, (Vararg,))
    t1 = _task(f1, 0, m)
    @test fetch(schedule(t1)) === ()

    # Test that _task validates argument types
    @test_throws TypeError Core._task(f1, "invalid_size")
    @test_throws TypeError Core._task(f1, "invalid_size", m)
    @test_throws ArgumentError Core._task(f1, 0, m, 1)
    @test_throws TypeError Core._task(f1, 0, "invalid")
    @test_throws TypeError Core._task(f1, 0, Int)
    @test_throws TypeError Core._task(f1, 0, nothing)
    mi = only(Base.specializations(which(f1, ())))
    @test mi isa Core.MethodInstance
    @test_throws TypeError Core._task(f1, 0, mi)
end