distributed_exec.jl

# This file is a part of Julia. License is MIT: https://julialang.org/license

using Test, Distributed, Random, Serialization, Sockets
import Distributed: launch, manage

@test cluster_cookie() isa String

include(joinpath(Sys.BINDIR, "..", "share", "julia", "test", "testenv.jl"))

@test Distributed.extract_imports(:(begin; import Foo, Bar; let; using Baz; end; end)) ==
      Any[:(import Foo, Bar), :(using Baz)]

# Test a few "remote" invocations when no workers are present
@test remote(myid)() == 1
@test pmap(identity, 1:100) == [1:100...]
@test 100 == @distributed (+) for i in 1:100
        1
    end

addprocs_with_testenv(4)
@test nprocs() == 5

# distributed loading of packages

# setup
@everywhere begin
    old_act_proj = Base.ACTIVE_PROJECT[]
    pushfirst!(Base.LOAD_PATH, "@")
    Base.ACTIVE_PROJECT[] = joinpath(Sys.BINDIR, "..", "share", "julia", "test", "TestPkg")
end

# cause precompilation of TestPkg to avoid race condition
Base.compilecache(Base.identify_package("TestPkg"))

@everywhere using TestPkg
@everywhere using TestPkg

@everywhere begin
    Base.ACTIVE_PROJECT[] = old_act_proj
    popfirst!(Base.LOAD_PATH)
end

@everywhere using Test, Random, LinearAlgebra

id_me = myid()
id_other = filter(x -> x != id_me, procs())[rand(1:(nprocs()-1))]

# Test remote()
let
    pool = default_worker_pool()

    count = 0
    count_condition = Condition()

    function remote_wait(c)
        @async begin
            count += 1
            remote(take!)(c)
            count -= 1
            notify(count_condition)
        end
        yield()
    end

    testchannels = [RemoteChannel() for i in 1:nworkers()]
    testcount = 0
    @test isready(pool) == true
    for c in testchannels
        @test count == testcount
        remote_wait(c)
        testcount += 1
    end
    @test count == testcount
    @test isready(pool) == false

    for c in testchannels
        @test count == testcount
        put!(c, "foo")
        testcount -= 1
        wait(count_condition)
        @test count == testcount
        @test isready(pool) == true
    end

    @test count == 0

    for c in testchannels
        @test count == testcount
        remote_wait(c)
        testcount += 1
    end
    @test count == testcount
    @test isready(pool) == false

    for c in reverse(testchannels)
        @test count == testcount
        put!(c, "foo")
        testcount -= 1
        wait(count_condition)
        @test count == testcount
        @test isready(pool) == true
    end

    @test count == 0
end

# Test Futures
function testf(id)
    f=Future(id)
    @test isready(f) == false
    @test f.v === nothing
    put!(f, :OK)
    @test isready(f) == true
    @test f.v !== nothing

    @test_throws ErrorException put!(f, :OK) # Cannot put! to a already set future
    @test_throws MethodError take!(f) # take! is unsupported on a Future

    @test fetch(f) == :OK
end

testf(id_me)
testf(id_other)

# Distributed GC tests for Futures
function test_futures_dgc(id)
    f = remotecall(myid, id)
    fid = remoteref_id(f)

    # remote value should be deleted after a fetch
    @test remotecall_fetch(k->(yield();haskey(Distributed.PGRP.refs, k)), id, fid) == true
    @test f.v === nothing
    @test fetch(f) == id
    @test f.v !== nothing
    yield(); # flush gc msgs
    @test remotecall_fetch(k->(yield();haskey(Distributed.PGRP.refs, k)), id, fid) == false


    # if unfetched, it should be deleted after a finalize
    f = remotecall(myid, id)
    fid = remoteref_id(f)
    @test remotecall_fetch(k->(yield();haskey(Distributed.PGRP.refs, k)), id, fid) == true
    @test f.v === nothing
    finalize(f)
    yield(); # flush gc msgs
    @test remotecall_fetch(k->(yield();haskey(Distributed.PGRP.refs, k)), id, fid) == false
end

test_futures_dgc(id_me)
test_futures_dgc(id_other)

# if sent to another worker, it should not be deleted till all references are fetched.
wid1 = workers()[1]
wid2 = workers()[2]
f = remotecall(myid, wid1)
fid = remoteref_id(f)

fstore = RemoteChannel(wid2)
put!(fstore, f)

@test fetch(f) == wid1
@test remotecall_fetch(k->haskey(Distributed.PGRP.refs, k), wid1, fid) == true
remotecall_fetch(r->(fetch(fetch(r)); yield()), wid2, fstore)
sleep(0.5) # to ensure that wid2 gc messages have been executed on wid1
@test remotecall_fetch(k->haskey(Distributed.PGRP.refs, k), wid1, fid) == false

# put! should release remote reference since it would have been cached locally
f = Future(wid1)
fid = remoteref_id(f)

# should not be created remotely till accessed
@test remotecall_fetch(k->haskey(Distributed.PGRP.refs, k), wid1, fid) == false
# create it remotely
isready(f)

@test remotecall_fetch(k->haskey(Distributed.PGRP.refs, k), wid1, fid) == true
put!(f, :OK)
@test remotecall_fetch(k->haskey(Distributed.PGRP.refs, k), wid1, fid) == false
@test fetch(f) == :OK

# RemoteException should be thrown on a put! when another process has set the value
f = Future(wid1)
fid = remoteref_id(f)

fstore = RemoteChannel(wid2)
put!(fstore, f) # send f to wid2
put!(f, :OK) # set value from master

@test remotecall_fetch(k->haskey(Distributed.PGRP.refs, k), wid1, fid) == true

testval = remotecall_fetch(wid2, fstore) do x
    try
        put!(fetch(x), :OK)
        return 0
    catch e
        if isa(e, RemoteException)
            return 1
        else
            return 2
        end
    end
end
@test testval == 1

# Issue number #25847
@everywhere function f25847(ref)
    fetch(ref)
    return true
end

f = remotecall_wait(identity, id_other, ones(10))
rrid = Distributed.RRID(f.whence, f.id)
remotecall_fetch(f25847, id_other, f)
@test BitSet([id_me]) == remotecall_fetch(()->Distributed.PGRP.refs[rrid].clientset, id_other)

remotecall_fetch(f25847, id_other, f)
@test BitSet([id_me]) == remotecall_fetch(()->Distributed.PGRP.refs[rrid].clientset, id_other)

finalize(f)
yield() # flush gc msgs
@test false == remotecall_fetch(chk_rrid->(yield(); haskey(Distributed.PGRP.refs, chk_rrid)), id_other, rrid)


# Distributed GC tests for RemoteChannels
function test_remoteref_dgc(id)
    rr = RemoteChannel(id)
    put!(rr, :OK)
    rrid = remoteref_id(rr)

    # remote value should be deleted after finalizing the ref
    @test remotecall_fetch(k->(yield();haskey(Distributed.PGRP.refs, k)), id, rrid) == true
    @test fetch(rr) == :OK
    @test remotecall_fetch(k->(yield();haskey(Distributed.PGRP.refs, k)), id, rrid) == true
    finalize(rr)
    yield(); # flush gc msgs
    @test remotecall_fetch(k->(yield();haskey(Distributed.PGRP.refs, k)), id, rrid) == false
end
test_remoteref_dgc(id_me)
test_remoteref_dgc(id_other)

# if sent to another worker, it should not be deleted till the other worker has also finalized.
let wid1 = workers()[1],
    wid2 = workers()[2],
    rr = RemoteChannel(wid1),
    rrid = remoteref_id(rr),
    fstore = RemoteChannel(wid2)

    put!(fstore, rr)
    @test remotecall_fetch(k -> haskey(Distributed.PGRP.refs, k), wid1, rrid) == true
    finalize(rr) # finalize locally
    yield() # flush gc msgs
    @test remotecall_fetch(k -> haskey(Distributed.PGRP.refs, k), wid1, rrid) == true
    remotecall_fetch(r -> (finalize(take!(r)); yield(); nothing), wid2, fstore) # finalize remotely
    sleep(0.5) # to ensure that wid2 messages have been executed on wid1
    @test remotecall_fetch(k -> haskey(Distributed.PGRP.refs, k), wid1, rrid) == false
end

# Tests for issue #23109 - should not hang.
f = @spawnat :any rand(1, 1)
@sync begin
    for _ in 1:10
        @async fetch(f)
    end
end

wid1, wid2 = workers()[1:2]
f = @spawnat wid1 rand(1,1)
@sync begin
    @async fetch(f)
    @async remotecall_fetch(()->fetch(f), wid2)
end


@test fetch(@spawnat id_other myid()) == id_other
@test (@fetchfrom id_other myid()) == id_other

pids=[]
for i in 1:nworkers()
    push!(pids, @fetch myid())
end
@test sort(pids) == sort(workers())


# test getindex on Futures and RemoteChannels
function test_indexing(rr)
    a = rand(5,5)
    put!(rr, a)
    @test rr[2,3] == a[2,3]
    @test rr[] == a
end

test_indexing(Future())
test_indexing(Future(id_other))
test_indexing(RemoteChannel())
test_indexing(RemoteChannel(id_other))

# Test ser/deser to non-ClusterSerializer objects.
function test_regular_io_ser(ref::Distributed.AbstractRemoteRef)
    io = IOBuffer()
    serialize(io, ref)
    seekstart(io)
    ref2 = deserialize(io)
    for fld in fieldnames(typeof(ref))
        v = getfield(ref2, fld)
        if isa(v, Number)
            @test v === zero(typeof(v))
        elseif v !== nothing
            error(string("Add test for field ", fld))
        end
    end
end

test_regular_io_ser(Future())
test_regular_io_ser(RemoteChannel())

# Test @distributed load balancing - all processors should get either M or M+1
# iterations out of the loop range for some M.
ids = @distributed((a,b)->[a;b], for i=1:7; myid(); end)
workloads = Int[sum(ids .== i) for i in 2:nprocs()]
@test maximum(workloads) - minimum(workloads) <= 1

# @distributed reduction should work even with very short ranges
@test @distributed(+, for i=1:2; i; end) == 3

@test_throws ArgumentError sleep(-1)
@test_throws ArgumentError timedwait(()->false, 0.1, pollint=-0.5)

# specify pids for pmap
@test sort(workers()[1:2]) == sort(unique(pmap(x->(sleep(0.1);myid()), WorkerPool(workers()[1:2]), 1:10)))

# Testing buffered  and unbuffered reads
# This large array should write directly to the socket
a = fill(1, 10^6)
@test a == remotecall_fetch((x)->x, id_other, a)

# Not a bitstype, should be buffered
s = [randstring() for x in 1:10^5]
@test s == remotecall_fetch((x)->x, id_other, s)

#large number of small requests
num_small_requests = 10000
@test fill(id_other, num_small_requests) == [remotecall_fetch(myid, id_other) for i in 1:num_small_requests]

# test parallel sends of large arrays from multiple tasks to the same remote worker
ntasks = 10
rr_list = [Channel(1) for x in 1:ntasks]

for rr in rr_list
    local rr
    let rr = rr
        @async try
            for i in 1:10
                a = rand(2*10^5)
                @test a == remotecall_fetch(x->x, id_other, a)
                yield()
            end
            put!(rr, :OK)
        catch
            put!(rr, :ERROR)
        end
    end
end

@test [fetch(rr) for rr in rr_list] == [:OK for x in 1:ntasks]

function test_channel(c)
    @test isopen(c) == true
    put!(c, 1)
    put!(c, "Hello")
    put!(c, 5.0)

    @test isready(c) == true
    @test isopen(c) == true
    @test fetch(c) == 1
    @test fetch(c) == 1   # Should not have been popped previously
    @test take!(c) == 1
    @test take!(c) == "Hello"
    @test fetch(c) == 5.0
    @test take!(c) == 5.0
    @test isready(c) == false
    @test isopen(c) == true
    close(c)
    @test isopen(c) == false
end

test_channel(Channel(10))
test_channel(RemoteChannel(()->Channel(10)))

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

# test channel iterations
function test_iteration(in_c, out_c)
    t=@async for v in in_c
        put!(out_c, v)
    end

    @test isopen(in_c) == true
    put!(in_c, 1)
    @test take!(out_c) == 1
    put!(in_c, "Hello")
    close(in_c)
    @test take!(out_c) == "Hello"
    @test isopen(in_c) == false
    @test_throws InvalidStateException put!(in_c, :foo)
    yield()
    @test istaskdone(t) == true
end

test_iteration(Channel(10), Channel(10))
# make sure exceptions propagate when waiting on Tasks
@test_throws CompositeException (@sync (@async error("oops")))
try
    @sync begin
        for i in 1:5
            @async error(i)
        end
    end
    error("unexpected")
catch ex
    @test typeof(ex) == CompositeException
    @test length(ex) == 5
    @test typeof(ex.exceptions[1]) == TaskFailedException
    @test typeof(ex.exceptions[1].task.exception) == ErrorException
    # test start, next, and done
    for (i, i_ex) in enumerate(ex)
        @test i == parse(Int, i_ex.task.exception.msg)
    end
    # test showerror
    err_str = sprint(showerror, ex)
    err_one_str = sprint(showerror, ex.exceptions[1])
    @test err_str == err_one_str * "\n\n...and 4 more exception(s).\n"
end
@test sprint(showerror, CompositeException()) == "CompositeException()\n"

function test_remoteexception_thrown(expr)
    try
        expr()
        error("unexpected")
    catch ex
        @test typeof(ex) == RemoteException
        @test typeof(ex.captured) == CapturedException
        @test typeof(ex.captured.ex) == ErrorException
        @test ex.captured.ex.msg == "foobar"
    end
end

for id in [id_other, id_me]
    local id
    test_remoteexception_thrown() do
        remotecall_fetch(id) do
            throw(ErrorException("foobar"))
        end
    end
    test_remoteexception_thrown() do
        remotecall_wait(id) do
            throw(ErrorException("foobar"))
        end
    end
    test_remoteexception_thrown() do
        wait(remotecall(id) do
            throw(ErrorException("foobar"))
        end)
    end
end

# make sure the stackframe from the remote error can be serialized
let ex
    try
        remotecall_fetch(id_other) do
            @eval module AModuleLocalToOther
                foo() = throw(ErrorException("A.error"))
                foo()
            end
        end
    catch ex
    end
    @test (ex::RemoteException).pid == id_other
    @test ((ex.captured::CapturedException).ex::ErrorException).msg == "A.error"
    bt = ex.captured.processed_bt::Array{Any,1}
    @test length(bt) > 1
    frame, repeated = bt[1]::Tuple{Base.StackTraces.StackFrame, Int}
    @test frame.func == :foo
    @test frame.linfo === nothing
    @test repeated == 1
end

# pmap tests. Needs at least 4 processors dedicated to the below tests. Which we currently have
# since the distributed tests are now spawned as a separate set.

# Test all combinations of pmap keyword args.
pmap_args = [
                (:distributed, [:default, false]),
                (:batch_size, [:default,2]),
                (:on_error, [:default, e -> (e.msg == "foobar" ? true : rethrow())]),
                (:retry_delays, [:default, fill(0.001, 1000)]),
                (:retry_check, [:default, (s,e) -> (s,endswith(e.msg,"foobar"))]),
            ]

kwdict = Dict()
function walk_args(i)
    if i > length(pmap_args)
        kwargs = []
        for (k,v) in kwdict
            if v !== :default
                push!(kwargs, (k,v))
            end
        end

        data = 1:100

        testw = kwdict[:distributed] === false ? [1] : workers()

        if kwdict[:retry_delays] !== :default
            mapf = x -> iseven(myid()) ? error("notfoobar") : (x*2, myid())
            results_test = pmap_res -> begin
                results = [x[1] for x in pmap_res]
                pids = [x[2] for x in pmap_res]
                @test results == [2:2:200...]
                for p in testw
                    if isodd(p)
                        @test p in pids
                    else
                        @test !(p in pids)
                    end
                end
            end
        elseif kwdict[:on_error] === :default
            mapf = x -> (x*2, myid())
            results_test = pmap_res -> begin
                results = [x[1] for x in pmap_res]
                pids = [x[2] for x in pmap_res]
                @test results == [2:2:200...]
                for p in testw
                    @test p in pids
                end
            end
        else
            mapf = x -> iseven(x) ? error("foobar") : (x*2, myid())
            results_test = pmap_res -> begin
                w = testw
                for (idx,x) in enumerate(data)
                    if iseven(x)
                        @test pmap_res[idx] == true
                    else
                        @test pmap_res[idx][1] == x*2
                        @test pmap_res[idx][2] in w
                    end
                end
            end
        end

        try
            results_test(pmap(mapf, data; kwargs...))
        catch
            println("pmap executing with args : ", kwargs)
            rethrow()
        end

        return
    end

    kwdict[pmap_args[i][1]] = pmap_args[i][2][1]
    walk_args(i+1)

    kwdict[pmap_args[i][1]] = pmap_args[i][2][2]
    walk_args(i+1)
end

# Start test for various kw arg combinations
walk_args(1)

include(joinpath(Sys.BINDIR, "..", "share", "julia", "test", "generic_map_tests.jl"))
empty_pool = WorkerPool([myid()])
pmap_fallback = (f, c...) -> pmap(f, empty_pool, c...)
generic_map_tests(pmap_fallback)

# pmap with various types. Test for equivalence with map
run_map_equivalence_tests(pmap)
@test pmap(uppercase, "Hello World!") == map(uppercase, "Hello World!")


# Simple test for pmap throws error
let error_thrown = false
    try
        pmap(x -> x == 50 ? error("foobar") : x, 1:100)
    catch e
        @test e.captured.ex.msg == "foobar"
        error_thrown = true
    end
    @test error_thrown
end

# Test pmap with a generator type iterator
@test [1:100...] == pmap(x->x, Base.Generator(x->(sleep(0.0001); x), 1:100))

# Test pgenerate
n = 10
as = [rand(4,4) for i in 1:n]
bs = deepcopy(as)
cs = collect(Distributed.pgenerate(x->(sleep(rand()*0.1); svd(x)), bs))
svdas = map(svd, as)
for i in 1:n
    @test cs[i].U ≈ svdas[i].U
    @test cs[i].S ≈ svdas[i].S
    @test cs[i].V ≈ svdas[i].V
end

# Test that the default worker pool cycles through all workers
pmap(_->myid(), 1:nworkers())  # priming run
@test nworkers() == length(unique(pmap(_->myid(), 1:100)))

# Test same behaviour when executed on a worker
@test nworkers() == length(unique(remotecall_fetch(()->pmap(_->myid(), 1:100), id_other)))

# Same tests with custom worker pools.
wp = WorkerPool(workers())
@test nworkers() == length(unique(pmap(_->myid(), wp, 1:100)))
@test nworkers() == length(unique(remotecall_fetch(wp->pmap(_->myid(), wp, 1:100), id_other, wp)))


# CachingPool tests
wp = CachingPool(workers())
@test [1:100...] == pmap(x->x, wp, 1:100)

clear!(wp)
@test length(wp.map_obj2ref) == 0

# The below block of tests are usually run only on local development systems, since:
# - tests which print errors
# - addprocs tests are memory intensive
# - ssh addprocs requires sshd to be running locally with passwordless login enabled.
# The test block is enabled by defining env JULIA_TESTFULL=1

DoFullTest = Bool(parse(Int,(get(ENV, "JULIA_TESTFULL", "0"))))

if DoFullTest
    println("Testing exception printing on remote worker from a `remote_do` call")
    println("Please ensure the remote error and backtrace is displayed on screen")

    remote_do(id_other) do
        throw(ErrorException("TESTING EXCEPTION ON REMOTE DO. PLEASE IGNORE"))
    end
    sleep(0.5)  # Give some time for the above error to be printed

    println("\n\nThe following 'invalid connection credentials' error messages are to be ignored.")
    all_w = workers()
    # Test sending fake data to workers. The worker processes will print an
    # error message but should not terminate.
    for w in Distributed.PGRP.workers
        if isa(w, Distributed.Worker)
            local s = connect(w.config.host, w.config.port)
            write(s, randstring(32))
        end
    end
    @test workers() == all_w
    @test all([p == remotecall_fetch(myid, p) for p in all_w])

if Sys.isunix() # aka have ssh
    function test_n_remove_pids(new_pids)
        for p in new_pids
            w_in_remote = sort(remotecall_fetch(workers, p))
            try
                @test intersect(new_pids, w_in_remote) == new_pids
            catch
                print("p       :     $p\n")
                print("newpids :     $new_pids\n")
                print("w_in_remote : $w_in_remote\n")
                print("intersect   : $(intersect(new_pids, w_in_remote))\n\n\n")
                rethrow()
            end
        end

        remotecall_fetch(rmprocs, 1, new_pids)
    end

    print("\n\nTesting SSHManager. A minimum of 4GB of RAM is recommended.\n")
    print("Please ensure: \n")
    print("1) sshd is running locally with passwordless login enabled.\n")
    print("2) Env variable USER is defined and is the ssh user.\n")
    print("3) Port 9300 is not in use.\n")

    sshflags = `-o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -o LogLevel=ERROR `
    #Issue #9951
    hosts=[]
    localhost_aliases = ["localhost", string(getipaddr()), "127.0.0.1"]
    num_workers = parse(Int,(get(ENV, "JULIA_ADDPROCS_NUM", "9")))

    for i in 1:(num_workers/length(localhost_aliases))
        append!(hosts, localhost_aliases)
    end

    print("\nTesting SSH addprocs with $(length(hosts)) workers...\n")
    new_pids = addprocs_with_testenv(hosts; sshflags=sshflags)
    @test length(new_pids) == length(hosts)
    test_n_remove_pids(new_pids)

    print("\nMixed ssh addprocs with :auto\n")
    new_pids = addprocs_with_testenv(["localhost", ("127.0.0.1", :auto), "localhost"]; sshflags=sshflags)
    @test length(new_pids) == (2 + Sys.CPU_THREADS)
    test_n_remove_pids(new_pids)

    print("\nMixed ssh addprocs with numeric counts\n")
    new_pids = addprocs_with_testenv([("localhost", 2), ("127.0.0.1", 2), "localhost"]; sshflags=sshflags)
    @test length(new_pids) == 5
    test_n_remove_pids(new_pids)

    print("\nssh addprocs with tunnel\n")
    new_pids = addprocs_with_testenv([("localhost", num_workers)]; tunnel=true, sshflags=sshflags)
    @test length(new_pids) == num_workers
    test_n_remove_pids(new_pids)

    print("\nAll supported formats for hostname\n")
    h1 = "localhost"
    user = ENV["USER"]
    h2 = "$user@$h1"
    h3 = "$h2:22"
    h4 = "$h3 $(string(getipaddr()))"
    h5 = "$h4:9300"

    new_pids = addprocs_with_testenv([h1, h2, h3, h4, h5]; sshflags=sshflags)
    @test length(new_pids) == 5
    test_n_remove_pids(new_pids)

    print("\nkeyword arg exename\n")
    for exename in [`$(joinpath(Sys.BINDIR, Base.julia_exename()))`, "$(joinpath(Sys.BINDIR, Base.julia_exename()))"]
        for addp_func in [()->addprocs_with_testenv(["localhost"]; exename=exename, exeflags=test_exeflags, sshflags=sshflags),
                          ()->addprocs_with_testenv(1; exename=exename, exeflags=test_exeflags)]

            local new_pids = addp_func()
            @test length(new_pids) == 1
            test_n_remove_pids(new_pids)
        end
    end

end # unix-only
end # full-test

let t = @task 42
    schedule(t, ErrorException(""), error=true)
    @test_throws TaskFailedException(t) Base.wait(t)
end

# issue #8207
let A = Any[]
    @distributed (+) for i in (push!(A,1); 1:2)
        i
    end
    @test length(A) == 1
end

# issue #13168
function f13168(n)
    val = 0
    for i = 1:n
        val += sum(rand(n, n)^2)
    end
    return val
end
let t = schedule(@task f13168(100))
    @test t.state == :runnable
    @test t.queue !== nothing
    @test_throws ErrorException schedule(t)
    yield()
    @test t.state == :done
    @test t.queue === nothing
    @test_throws ErrorException schedule(t)
    @test isa(fetch(t), Float64)
end

# issue #13122
@test remotecall_fetch(identity, workers()[1], C_NULL) === C_NULL

# issue #11062
function t11062()
    @async v11062 = 1
    v11062 = 2
end

@test t11062() == 2

# issue #15406
v15406 = remotecall_wait(() -> 1, id_other)
fetch(v15406)
remotecall_wait(fetch, id_other, v15406)

# Test various forms of remotecall* invocations

@everywhere f_args(v1, v2=0; kw1=0, kw2=0) = v1+v2+kw1+kw2

function test_f_args(result, args...; kwargs...)
    @test fetch(remotecall(args...; kwargs...)) == result
    @test fetch(remotecall_wait(args...; kwargs...)) == result
    @test remotecall_fetch(args...; kwargs...) == result

    # A visual test - remote_do should NOT print any errors
    remote_do(args...; kwargs...)
end

for tid in [id_other, id_me, default_worker_pool()]
    test_f_args(1, f_args, tid, 1)
    test_f_args(3, f_args, tid, 1, 2)
    test_f_args(5, f_args, tid, 1; kw1=4)
    test_f_args(13, f_args, tid, 1; kw1=4, kw2=8)
    test_f_args(15, f_args, tid, 1, 2; kw1=4, kw2=8)
end

# Test remote_do
f=Future(id_me)
remote_do(fut->put!(fut, myid()), id_me, f)
@test fetch(f) == id_me

f=Future(id_other)
remote_do(fut->put!(fut, myid()), id_other, f)
@test fetch(f) == id_other

# Github issue #29932
rc_unbuffered = RemoteChannel(()->Channel{Vector{Float64}}(0))

@async begin
    # Trigger direct write (no buffering) of largish array
    array_sz = Int(Base.SZ_UNBUFFERED_IO/8) + 1
    largev = zeros(array_sz)
    for i in 1:10
        largev[1] = float(i)
        put!(rc_unbuffered, largev)
    end
end

@test remotecall_fetch(rc -> begin
        for i in 1:10
            take!(rc)[1] != float(i) && error("Failed")
        end
        return :OK
    end, id_other, rc_unbuffered) == :OK

# github PR #14456
n = DoFullTest ? 6 : 5
for i = 1:10^n
    fetch(@spawnat myid() myid())
end

# issue #15451
@test remotecall_fetch(x->(y->2y)(x)+1, workers()[1], 3) == 7

# issue #16091
mutable struct T16091 end
wid = workers()[1]
@test try
    remotecall_fetch(()->T16091, wid)
    false
catch ex
    ((ex::RemoteException).captured::CapturedException).ex === UndefVarError(:T16091)
end
@test try
    remotecall_fetch(identity, wid, T16091)
    false
catch ex
    ((ex::RemoteException).captured::CapturedException).ex === UndefVarError(:T16091)
end

f16091a() = 1
remotecall_fetch(()->eval(:(f16091a() = 2)), wid)
@test remotecall_fetch(f16091a, wid) === 2
@test remotecall_fetch((myid)->remotecall_fetch(f16091a, myid), wid, myid()) === 1

# these will only heisen-fail, since it depends on the gensym counter collisions:
f16091b = () -> 1
remotecall_fetch(()->eval(:(f16091b = () -> 2)), wid)
@test remotecall_fetch(f16091b, 2) === 1
# Global anonymous functions are over-written...
@test remotecall_fetch((myid)->remotecall_fetch(f16091b, myid), wid, myid()) === 1

# ...while local anonymous functions are by definition, local.
let
    f16091c = () -> 1
    @test remotecall_fetch(f16091c, 2) === 1
    @test remotecall_fetch(
        myid -> begin
            let
                f16091c = () -> 2
                remotecall_fetch(f16091c, myid)
            end
        end, wid, myid()) === 2
end

# issue #16451
rng=RandomDevice()
retval = @distributed (+) for _ in 1:10
    rand(rng)
end
@test retval > 0.0 && retval < 10.0

rand(rng)
retval = @distributed (+) for _ in 1:10
    rand(rng)
end
@test retval > 0.0 && retval < 10.0

# serialization tests
wrkr1 = workers()[1]
wrkr2 = workers()[end]

@test remotecall_fetch(p->remotecall_fetch(myid, p), wrkr1, wrkr2) == wrkr2

# Send f to wrkr1 and wrkr2. Then try calling f on wrkr2 from wrkr1
f_myid = ()->myid()
@test wrkr1 == remotecall_fetch(f_myid, wrkr1)
@test wrkr2 == remotecall_fetch(f_myid, wrkr2)
@test wrkr2 == remotecall_fetch((f, p)->remotecall_fetch(f, p), wrkr1, f_myid, wrkr2)

# Deserialization error recovery test
# locally defined module, but unavailable on workers
module LocalFoo
    global foo=1
end

let
    @test_throws RemoteException remotecall_fetch(()->LocalFoo.foo, 2)

    bad_thunk = ()->NonexistantModule.f()
    @test_throws RemoteException remotecall_fetch(bad_thunk, 2)

    # Test that the stream is still usable
    @test remotecall_fetch(()->:test,2) == :test
    ref = remotecall(bad_thunk, 2)
    @test_throws RemoteException fetch(ref)
end

# Test calling @everywhere from a module not defined on the workers
module LocalBar
    using Distributed
    bar() = @everywhere new_bar()=myid()
end
LocalBar.bar()
for p in procs()
    @test p == remotecall_fetch(new_bar, p)
end

# @everywhere (remotecall_eval) behaviors (#22589)
let (p, p2) = filter!(p -> p != myid(), procs())
    @test (myid() + 1) == @everywhere myid() (myid() + 1)
    @test (p * 2) == @everywhere p (myid() * 2)
    @test 1 == @everywhere p defined_on_p = 1
    @test !@isdefined defined_on_p
    @test !isdefined(Main, :defined_on_p)
    @test remotecall_fetch(isdefined, p, Main, :defined_on_p)
    @test !remotecall_fetch(isdefined, p2, Main, :defined_on_p)
    @test nothing === @everywhere [p, p] defined_on_p += 1
    @test 3 === @everywhere p defined_on_p
    let ref = Ref(0)
        @test nothing ===
            @everywhere [myid(), p, myid(), myid(), p] begin
                Test.@test Main === @__MODULE__
                $ref[] += 1
            end
        @test ref[] == 3
    end
    function test_throw_on(procs, msg)
        try
            @everywhere procs error($msg)
            error("test failed to throw")
        catch excpt
            if procs isa Int
                ex = Any[excpt]
            else
                ex = (excpt::CompositeException).exceptions
            end
            for (p, ex) in zip(procs, ex)
                local p
                if procs isa Int || p != myid()
                    @test (ex::RemoteException).pid == p
                    ex = ((ex::RemoteException).captured::CapturedException).ex
                else
                    ex = (ex::TaskFailedException).task.exception
                end
                @test (ex::ErrorException).msg == msg
            end
        end
    end
    test_throw_on(p, "everywhere on p")
    test_throw_on(myid(), "everywhere on myid")
    test_throw_on([p, myid()], "everywhere on myid and p")
    test_throw_on([p2, p], "everywhere on p and p2")
end

# Test addprocs enable_threaded_blas parameter

const get_num_threads = function() # anonymous so it will be serialized when called
    blas = LinearAlgebra.BLAS.vendor()
    # Wrap in a try to catch unsupported blas versions
    try
        if blas == :openblas
            return ccall((:openblas_get_num_threads, Base.libblas_name), Cint, ())
        elseif blas == :openblas64
            return ccall((:openblas_get_num_threads64_, Base.libblas_name), Cint, ())
        elseif blas == :mkl
            return ccall((:MKL_Get_Max_Num_Threads, Base.libblas_name), Cint, ())
        end

        # OSX BLAS looks at an environment variable
        if Sys.isapple()
            return tryparse(Cint, get(ENV, "VECLIB_MAXIMUM_THREADS", "1"))
        end
    catch
    end

    return nothing
end

function get_remote_num_threads(processes_added)
    return [remotecall_fetch(get_num_threads, proc_id) for proc_id in processes_added]
end

function test_blas_config(pid, expected)
    for worker in Distributed.PGRP.workers
        if worker.id == pid
            @test worker.config.enable_threaded_blas == expected
            return
        end
    end
end

function test_add_procs_threaded_blas()
    master_blas_thread_count = get_num_threads()
    if master_blas_thread_count === nothing
        @warn "Skipping blas num threads tests due to unsupported blas version"
        return
    end
    @test master_blas_thread_count <= 8 # check that Base set the environment variable in __init__ before LinearAlgebra dlopen'd it

    # Test with default enable_threaded_blas false
    processes_added = addprocs_with_testenv(2)
    for proc_id in processes_added
        test_blas_config(proc_id, false)
    end

    # Master thread should not have changed
    @test get_num_threads() == master_blas_thread_count

    # Threading disabled in children by default
    thread_counts_by_process = get_remote_num_threads(processes_added)
    for thread_count in thread_counts_by_process
        @test thread_count == 1
    end
    rmprocs(processes_added)

    processes_added = addprocs_with_testenv(2, enable_threaded_blas=true)
    for proc_id in processes_added
        test_blas_config(proc_id, true)
    end

    @test get_num_threads() == master_blas_thread_count

    # BLAS.set_num_threads(`num`) doesn't  cause get_num_threads to return `num`
    # depending on the machine, the BLAS version, and BLAS configuration, so
    # we need a very lenient test.
    thread_counts_by_process = get_remote_num_threads(processes_added)
    for thread_count in thread_counts_by_process
        @test thread_count >= 1
    end
    rmprocs(processes_added)
end
test_add_procs_threaded_blas()

#19687
# ensure no race conditions between rmprocs and addprocs
for i in 1:5
    p = addprocs_with_testenv(1)[1]
    @spawnat p sleep(5)
    rmprocs(p; waitfor=0)
end

# Test if a wait has been called on rmprocs(...;waitfor=0), further remotecalls
# don't throw errors.
for i in 1:5
    p = addprocs_with_testenv(1)[1]
    np = nprocs()
    @spawnat p sleep(5)
    Base.wait(rmprocs(p; waitfor=0))
    for pid in procs()
        @test pid == remotecall_fetch(myid, pid)
    end
    @test nprocs() == np - 1
end

# Test that an exception is thrown if workers are unable to be removed within requested time.
if DoFullTest
    pids=addprocs_with_testenv(4);
    @test_throws ErrorException rmprocs(pids; waitfor=0.001);
    # wait for workers to be removed
    while any(in(procs()), pids)
        sleep(0.1)
    end
end

# Test addprocs/rmprocs from master node only
for f in [ ()->addprocs(1; exeflags=test_exeflags), ()->rmprocs(workers()) ]
    local f
    try
        remotecall_fetch(f, id_other)
        error("Unexpected")
    catch ex
        @test isa(ex, RemoteException)
        @test ex.captured.ex.msg == "Only process 1 can add and remove workers"
    end
end

# Test the following addprocs error conditions
# - invalid host name - github issue #20372
# - julia exe exiting with an error
# - timeout reading host:port from worker stdout
# - host:port not found in worker stdout in the first 1000 lines

struct ErrorSimulator <: ClusterManager
    mode
end

function launch(manager::ErrorSimulator, params::Dict, launched::Array, c::Condition)
    exename = params[:exename]
    dir = params[:dir]

    cmd = `$(Base.julia_cmd(exename)) --startup-file=no`
    if manager.mode == :timeout
        cmd = `$cmd -e "sleep(10)"`
    elseif manager.mode == :ntries
        cmd = `$cmd -e "[println(x) for x in 1:1001]"`
    elseif manager.mode == :exit
        cmd = `$cmd -e "exit(-1)"`
    else
        error("Unknown mode")
    end
    io = open(detach(setenv(cmd, dir=dir)))

    wconfig = WorkerConfig()
    wconfig.process = io
    wconfig.io = io.out
    push!(launched, wconfig)
    notify(c)
end

testruns = Any[]

if DoFullTest
    append!(testruns, [(()->addprocs_with_testenv(["errorhost20372"]), "Unable to read host:port string from worker. Launch command exited with error?", ())])
end

append!(testruns, [
    (()->addprocs_with_testenv(ErrorSimulator(:exit)), "Unable to read host:port string from worker. Launch command exited with error?", ()),
    (()->addprocs_with_testenv(ErrorSimulator(:ntries)), "Unexpected output from worker launch command. Host:port string not found.", ()),
    (()->addprocs_with_testenv(ErrorSimulator(:timeout)), "Timed out waiting to read host:port string from worker.", ("JULIA_WORKER_TIMEOUT"=>"1",))
])

for (addp_testf, expected_errstr, env) in testruns
    old_stdout = stdout
    stdout_out, stdout_in = redirect_stdout()
    stdout_txt = @async filter!(readlines(stdout_out)) do s
            return !startswith(s, "\tFrom worker startup:\t")
        end
    try
        withenv(env...) do
            addp_testf()
        end
        error("Unexpected")
    catch ex
        redirect_stdout(old_stdout)
        close(stdout_in)
        @test isempty(fetch(stdout_txt))
        @test isa(ex, CompositeException)
        @test ex.exceptions[1].task.exception.msg == expected_errstr
    end
end


# Auto serialization of globals from Main.
# bitstypes
global v1 = 1
@test remotecall_fetch(()->v1, id_other) == v1
@test remotecall_fetch(()->isdefined(Main, :v1), id_other)
for i in 2:5
    global v1 = i
    @test remotecall_fetch(()->v1, id_other) == i
end

# non-bitstypes
global v2 = zeros(10)
for i in 1:5
    v2[i] = i
    @test remotecall_fetch(()->v2, id_other) == v2
end

# Different global bindings to the same object
global v3 = fill(1., 10)
global v4 = v3
@test remotecall_fetch(()->v3, id_other) == remotecall_fetch(()->v4, id_other)
@test remotecall_fetch(()->isdefined(Main, :v3), id_other)
@test remotecall_fetch(()->isdefined(Main, :v4), id_other)

# Global references to Types and Modules should work if they are locally defined
global v5 = Int
global v6 = Distributed
@test remotecall_fetch(()->v5, id_other) === Int
@test remotecall_fetch(()->v6, id_other) === Distributed

struct FooStructLocal end
module FooModLocal end
v5 = FooStructLocal
v6 = FooModLocal
@test_throws RemoteException remotecall_fetch(()->v5, id_other)
@test_throws RemoteException remotecall_fetch(()->v6, id_other)

@everywhere struct FooStructEverywhere end
@everywhere module FooModEverywhere end
v5 = FooStructEverywhere
v6 = FooModEverywhere
@test remotecall_fetch(()->v5, id_other) === FooStructEverywhere
@test remotecall_fetch(()->v6, id_other) === FooModEverywhere

# hash value same but different object instance
v7 = ones(10)
oid1 = objectid(v7)
hval1 = hash(v7)
@test v7 == @fetchfrom id_other v7
remote_oid1 = @fetchfrom id_other objectid(v7)

v7 = ones(10)
@test oid1 != objectid(v7)
@test hval1 == hash(v7)
@test remote_oid1 != @fetchfrom id_other objectid(v7)


# Github issue #31252
v31252 = :a
@test :a == @fetchfrom id_other v31252

v31252 = :b
@test :b == @fetchfrom id_other v31252

v31252 = :a
@test :a == @fetchfrom id_other v31252


# Test that a global is not being repeatedly serialized when
# a) referenced multiple times in the closure
# b) hash value has not changed.

@everywhere begin
    using Serialization
    global testsercnt_d = Dict()
    mutable struct TestSerCnt
        v
    end
    import Base.hash, Base.==
    hash(x::TestSerCnt, h::UInt) = hash(hash(x.v), h)
    ==(x1::TestSerCnt, x2::TestSerCnt) = (x1.v == x2.v)

    function Serialization.serialize(s::AbstractSerializer, t::TestSerCnt)
        Serialization.serialize_type(s, TestSerCnt)
        serialize(s, t.v)
        global testsercnt_d
        cnt = get!(testsercnt_d, objectid(t), 0)
        testsercnt_d[objectid(t)] = cnt+1
    end

    Serialization.deserialize(s::AbstractSerializer, ::Type{TestSerCnt}) = TestSerCnt(deserialize(s))
end

# hash value of tsc is not changed
global tsc = TestSerCnt(zeros(10))
for i in 1:5
    remotecall_fetch(()->tsc, id_other)
end
# should have been serialized only once
@test testsercnt_d[objectid(tsc)] == 1

# hash values are changed
n=5
testsercnt_d[objectid(tsc)] = 0
for i in 1:n
    tsc.v[i] = i
    remotecall_fetch(()->tsc, id_other)
end
# should have been serialized as many times as the loop
@test testsercnt_d[objectid(tsc)] == n

# Multiple references in a closure should be serialized only once.
global mrefs = TestSerCnt(fill(1.,10))
@test remotecall_fetch(()->(mrefs.v, 2*mrefs.v, 3*mrefs.v), id_other) == (fill(1.,10), fill(2.,10), fill(3.,10))
@test testsercnt_d[objectid(mrefs)] == 1


# nested anon functions
global f1 = x->x
global f2 = x->f1(x)
v = rand()
@test remotecall_fetch(f2, id_other, v) == v
@test remotecall_fetch(x->f2(x), id_other, v) == v

# consts
const c1 = fill(1., 10)
@test remotecall_fetch(()->c1, id_other) == c1
@test remotecall_fetch(()->isconst(Main, :c1), id_other)

# Test same calls with local vars
function wrapped_var_ser_tests()
    # bitstypes
    local lv1 = 1
    @test remotecall_fetch(()->lv1, id_other) == lv1
    @test !remotecall_fetch(()->isdefined(Main, :lv1), id_other)
    for i in 2:5
        lv1 = i
        @test remotecall_fetch(()->lv1, id_other) == i
    end

    # non-bitstypes
    local lv2 = zeros(10)
    for i in 1:5
        lv2[i] = i
        @test remotecall_fetch(()->lv2, id_other) == lv2
    end

    # nested anon functions
    local lf1 = x->x
    local lf2 = x->lf1(x)
    v = rand()
    @test remotecall_fetch(lf2, id_other, v) == v
    @test remotecall_fetch(x->lf2(x), id_other, v) == v
end

wrapped_var_ser_tests()

# Test internal data structures being cleaned up upon gc.
global ids_cleanup = fill(1., 6)
global ids_func = ()->ids_cleanup

clust_ser = (Distributed.worker_from_id(id_other)).w_serializer
@test remotecall_fetch(ids_func, id_other) == ids_cleanup

# TODO Add test for cleanup from `clust_ser.glbs_in_tnobj`

# reported github issues - Mostly tests with globals and various distributed macros
#2669, #5390
v2669=10
@test fetch(@spawnat :any (1+v2669)) == 11

#12367
refs = []
if true
    n = 10
    for p in procs()
        push!(refs, @spawnat p begin
            @sync for i in 1:n
                nothing
            end
        end)
    end
end
foreach(wait, refs)

#6760
if true
    a = 2
    x = @distributed (vcat) for k=1:2
        sin(a)
    end
end
@test x == map(_->sin(2), 1:2)

let thrown = false
    try
        remotecall_fetch(sqrt, 2, -1)
    catch e
        thrown = true
        local b = IOBuffer()
        showerror(b, e)
        @test occursin("sqrt will only return", String(take!(b)))
    end
    @test thrown
end

#19463
function foo19463()
    w1 = workers()[1]
    w2 = workers()[2]
    w3 = workers()[3]

    b1 = () -> 1
    b2 = () -> fetch(@spawnat w1 b1()) + 1
    b3 = () -> fetch(@spawnat w2 b2()) + 1
    b4 = () -> fetch(@spawnat w3 b3()) + 1
    b4()
end
@test foo19463() == 4

# Testing clear!
function setup_syms(n, pids)
    syms = []
    for i in 1:n
        symstr = string("clrtest", randstring())
        sym = Symbol(symstr)
        eval(:(global $sym = rand()))
        for p in pids
            eval(:(@test $sym == remotecall_fetch(()->$sym, $p)))
            eval(:(@test remotecall_fetch(isdefined, $p, Main, Symbol($symstr))))
        end
        push!(syms, sym)
    end
    syms
end

function test_clear(syms, pids)
    for p in pids
        for sym in syms
            remote_val = remotecall_fetch(()->getfield(Main, sym), p)
            @test remote_val === nothing
            @test remote_val != getfield(Main, sym)
        end
    end
end

syms = setup_syms(1, [id_other])
clear!(syms[1], id_other)
test_clear(syms, [id_other])

syms = setup_syms(1, workers())
clear!(syms[1], workers())
test_clear(syms, workers())

syms = setup_syms(3, [id_other])
clear!(syms, id_other)
test_clear(syms, [id_other])

syms = setup_syms(3, workers())
clear!(syms, workers())
test_clear(syms, workers())

# Test partial recovery from a deserialization error in CapturedException
try
    expr = quote
                mutable struct DontExistOn1
                    x
                end
                throw(BoundsError(DontExistOn1(1), 1))
           end

    remotecall_fetch(()->eval(expr), id_other)
    error("unexpected")
catch ex
    @test isa(ex.captured.ex.exceptions[1].ex, ErrorException)
    @test occursin("BoundsError", ex.captured.ex.exceptions[1].ex.msg)
    @test ex.captured.ex.exceptions[2].ex == UndefVarError(:DontExistOn1)
end

let
    # creates a new worker in a different folder and tries to include file
    tmp_dir = mktempdir()
    tmp_dir2 = joinpath(tmp_dir, "2")
    tmp_file = joinpath(tmp_dir2, "testfile")
    tmp_file2 = joinpath(tmp_dir2, "testfile2")
    proc = addprocs_with_testenv(1, dir=tmp_dir)
    try
        mkdir(tmp_dir2)
        write(tmp_file, "23.32 + 32 + myid() + include(\"testfile2\")")
        write(tmp_file2, "myid() * 2")
        @test_throws(ErrorException("could not open file $(joinpath(@__DIR__, "testfile"))"),
                     include("testfile"))
        @test_throws(ErrorException("could not open file $(joinpath(@__DIR__, "testfile2"))"),
                     include("testfile2"))
        @test_throws(ErrorException("could not open file $(joinpath(@__DIR__, "2", "testfile"))"),
                     include("2/testfile"))
        @test include(tmp_file) == 58.32
        @test remotecall_fetch(include, proc[1], joinpath("2", "testfile")) == 55.32 + proc[1] * 3
    finally
        rmprocs(proc)
        rm(tmp_file, force=true)
        rm(tmp_file2, force=true)
        rm(tmp_dir2, force=true)
        #rm(tmp_dir, force=true)
    end
end
# cookie and command line option `--worker` tests. remove workers, set cookie and test
struct WorkerArgTester <: ClusterManager
    worker_opt
    write_cookie
end

function launch(manager::WorkerArgTester, params::Dict, launched::Array, c::Condition)
    dir = params[:dir]
    exename = params[:exename]
    exeflags = params[:exeflags]

    cmd = `$exename $exeflags --bind-to $(Distributed.LPROC.bind_addr) $(manager.worker_opt)`
    cmd = pipeline(detach(setenv(cmd, dir=dir)))
    io = open(cmd, "r+")
    manager.write_cookie && Distributed.write_cookie(io)

    wconfig = WorkerConfig()
    wconfig.process = io
    wconfig.io = io.out
    push!(launched, wconfig)

    notify(c)
end
manage(::WorkerArgTester, ::Integer, ::WorkerConfig, ::Symbol) = nothing

nprocs()>1 && rmprocs(workers())

npids = addprocs_with_testenv(WorkerArgTester(`--worker`, true))
@test remotecall_fetch(myid, npids[1]) == npids[1]
rmprocs(npids)

cluster_cookie("")  # An empty string is a valid cookie
npids = addprocs_with_testenv(WorkerArgTester(`--worker=`, false))
@test remotecall_fetch(myid, npids[1]) == npids[1]
rmprocs(npids)

cluster_cookie("foobar") # custom cookie
npids = addprocs_with_testenv(WorkerArgTester(`--worker=foobar`, false))
@test remotecall_fetch(myid, npids[1]) == npids[1]

# tests for start_worker options to retain stdio (issue #31035)
struct RetainStdioTester <: ClusterManager
    close_stdin::Bool
    stderr_to_stdout::Bool
end

function launch(manager::RetainStdioTester, params::Dict, launched::Array, c::Condition)
    dir = params[:dir]
    exename = params[:exename]
    exeflags = params[:exeflags]

    jlcmd = "using Distributed; start_worker(\"\"; close_stdin=$(manager.close_stdin), stderr_to_stdout=$(manager.stderr_to_stdout));"
    cmd = detach(setenv(`$exename $exeflags --bind-to $(Distributed.LPROC.bind_addr) -e $jlcmd`, dir=dir))
    proc = open(cmd, "r+")

    wconfig = WorkerConfig()
    wconfig.process = proc
    wconfig.io = proc.out
    push!(launched, wconfig)

    notify(c)
end
manage(::RetainStdioTester, ::Integer, ::WorkerConfig, ::Symbol) = nothing


nprocs()>1 && rmprocs(workers())
cluster_cookie("")

for close_stdin in (true, false), stderr_to_stdout in (true, false)
    npids = addprocs_with_testenv(RetainStdioTester(close_stdin,stderr_to_stdout))
    @test remotecall_fetch(myid, npids[1]) == npids[1]
    @test close_stdin != remotecall_fetch(()->isopen(stdin), npids[1])
    @test stderr_to_stdout == remotecall_fetch(()->(stderr === stdout), npids[1])
    rmprocs(npids)
end

# Issue # 22865
# Must be run on a new cluster, i.e., all workers must be in the same state.
rmprocs(workers())
p1,p2 = addprocs_with_testenv(2)
@everywhere f22865(p) = remotecall_fetch(x->x.*2, p, fill(1.,2))
@test fill(2.,2) == remotecall_fetch(f22865, p1, p2)

function reuseport_tests()
    # Run the test on all processes.
    results = asyncmap(procs()) do p
        remotecall_fetch(p) do
            ports_lower = []        # ports of pids lower than myid()
            ports_higher = []       # ports of pids higher than myid()
            for w in Distributed.PGRP.workers
                w.id == myid() && continue
                port = Sockets._sockname(w.r_stream, true)[2]
                if (w.id == 1)
                    # master connects to workers
                    push!(ports_higher, port)
                elseif w.id < myid()
                    push!(ports_lower, port)
                elseif w.id > myid()
                    push!(ports_higher, port)
                end
            end
            @assert (length(ports_lower) + length(ports_higher)) == nworkers()
            for portset in [ports_lower, ports_higher]
                if (length(portset) > 0) && (length(unique(portset)) != 1)
                    @warn "SO_REUSEPORT TESTS FAILED. UNSUPPORTED/OLDER UNIX VERSION?"
                    return 0
                end
            end
            return myid()
        end
    end

    # Ensure that the code has indeed been successfully executed everywhere
    @test all(in(results), procs())
end

# Test that the client port is reused. SO_REUSEPORT may not be supported on
# all UNIX platforms, Linux kernels prior to 3.9 and older versions of OSX
if ccall(:jl_has_so_reuseport, Int32, ()) == 1
    rmprocs(workers())
    addprocs_with_testenv(4; lazy=false)
    reuseport_tests()
else
    @info "SO_REUSEPORT is unsupported, skipping reuseport tests"
end

# issue #27933
a27933 = :_not_defined_27933
@test remotecall_fetch(()->a27933, first(workers())) === a27933

# PR #28651
for T in (UInt8, Int8, UInt16, Int16, UInt32, Int32, UInt64)
    n = @distributed (+) for i in Base.OneTo(T(10))
        i
    end
    @test n == 55
end

# issue #28966
let code = """
    import Distributed
    Distributed.addprocs(1)
    Distributed.@everywhere f() = myid()
    for w in Distributed.workers()
        @assert Distributed.remotecall_fetch(f, w) == w
    end
    """
    @test success(`$(Base.julia_cmd()) --startup-file=no -e $code`)
end

# PR 32431: tests for internal Distributed.head_and_tail
let (h, t) = Distributed.head_and_tail(1:10, 3)
    @test h == 1:3
    @test collect(t) == 4:10
end
let (h, t) = Distributed.head_and_tail(1:10, 0)
    @test h == []
    @test collect(t) == 1:10
end
let (h, t) = Distributed.head_and_tail(1:3, 5)
    @test h == 1:3
    @test collect(t) == []
end
let (h, t) = Distributed.head_and_tail(1:3, 3)
    @test h == 1:3
    @test collect(t) == []
end
let (h, t) = Distributed.head_and_tail(Int[], 3)
    @test h == []
    @test collect(t) == []
end
let (h, t) = Distributed.head_and_tail(Int[], 0)
    @test h == []
    @test collect(t) == []
end

# Run topology tests last after removing all workers, since a given
# cluster at any time only supports a single topology.
rmprocs(workers())
include("topology.jl")