-
-
Notifications
You must be signed in to change notification settings - Fork 5.5k
/
task.jl
1009 lines (871 loc) · 28.8 KB
/
task.jl
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
# This file is a part of Julia. License is MIT: https://julialang.org/license
## basic task functions and TLS
Core.Task(@nospecialize(f), reserved_stack::Int=0) = Core._Task(f, reserved_stack, ThreadSynchronizer())
# Container for a captured exception and its backtrace. Can be serialized.
struct CapturedException <: Exception
ex::Any
processed_bt::Vector{Any}
function CapturedException(ex, bt_raw::Vector)
# bt_raw MUST be a vector that can be processed by StackTraces.stacktrace
# Typically the result of a catch_backtrace()
# Process bt_raw so that it can be safely serialized
bt_lines = process_backtrace(bt_raw, 100) # Limiting this to 100 lines.
CapturedException(ex, bt_lines)
end
CapturedException(ex, processed_bt::Vector{Any}) = new(ex, processed_bt)
end
function showerror(io::IO, ce::CapturedException)
showerror(io, ce.ex, ce.processed_bt, backtrace=true)
end
"""
capture_exception(ex, bt) -> Exception
Returns an exception, possibly incorporating information from a backtrace `bt`. Defaults to returning [`CapturedException(ex, bt)`](@ref).
Used in [`asyncmap`](@ref) and [`asyncmap!`](@ref) to capture exceptions thrown during
the user-supplied function call.
"""
capture_exception(ex, bt) = CapturedException(ex, bt)
"""
CompositeException
Wrap a `Vector` of exceptions thrown by a [`Task`](@ref) (e.g. generated from a remote worker over a channel
or an asynchronously executing local I/O write or a remote worker under `pmap`) with information about the series of exceptions.
For example, if a group of workers are executing several tasks, and multiple workers fail, the resulting `CompositeException` will
contain a "bundle" of information from each worker indicating where and why the exception(s) occurred.
"""
struct CompositeException <: Exception
exceptions::Vector{Any}
CompositeException() = new(Any[])
CompositeException(exceptions) = new(exceptions)
end
length(c::CompositeException) = length(c.exceptions)
push!(c::CompositeException, ex) = push!(c.exceptions, ex)
pushfirst!(c::CompositeException, ex) = pushfirst!(c.exceptions, ex)
isempty(c::CompositeException) = isempty(c.exceptions)
iterate(c::CompositeException, state...) = iterate(c.exceptions, state...)
eltype(::Type{CompositeException}) = Any
function showerror(io::IO, ex::CompositeException)
if !isempty(ex)
showerror(io, ex.exceptions[1])
remaining = length(ex) - 1
if remaining > 0
print(io, "\n\n...and ", remaining, " more exception", remaining > 1 ? "s" : "", ".\n")
end
else
print(io, "CompositeException()\n")
end
end
"""
TaskFailedException
This exception is thrown by a [`wait(t)`](@ref) call when task `t` fails.
`TaskFailedException` wraps the failed task `t`.
"""
struct TaskFailedException <: Exception
task::Task
end
function showerror(io::IO, ex::TaskFailedException, bt = nothing; backtrace=true)
print(io, "TaskFailedException")
if bt !== nothing && backtrace
show_backtrace(io, bt)
end
println(io)
printstyled(io, "\n nested task error: ", color=error_color())
show_task_exception(io, ex.task)
end
function show_task_exception(io::IO, t::Task; indent = true)
stack = current_exceptions(t)
b = IOBuffer()
if isempty(stack)
# exception stack buffer not available; probably a serialized task
showerror(IOContext(b, io), t.result)
else
show_exception_stack(IOContext(b, io), stack)
end
str = String(take!(b))
if indent
str = replace(str, "\n" => "\n ")
end
print(io, str)
end
function show(io::IO, t::Task)
state = t.state
state_str = "$state" * ((state == :runnable && istaskstarted(t)) ? ", started" : "")
print(io, "Task ($state_str) @0x$(string(convert(UInt, pointer_from_objref(t)), base = 16, pad = Sys.WORD_SIZE>>2))")
end
"""
@task
Wrap an expression in a [`Task`](@ref) without executing it, and return the [`Task`](@ref). This only
creates a task, and does not run it.
# Examples
```jldoctest
julia> a1() = sum(i for i in 1:1000);
julia> b = @task a1();
julia> istaskstarted(b)
false
julia> schedule(b);
julia> yield();
julia> istaskdone(b)
true
```
"""
macro task(ex)
thunk = Base.replace_linenums!(:(()->$(esc(ex))), __source__)
:(Task($thunk))
end
"""
current_task()
Get the currently running [`Task`](@ref).
"""
current_task() = ccall(:jl_get_current_task, Ref{Task}, ())
# task states
const task_state_runnable = UInt8(0)
const task_state_done = UInt8(1)
const task_state_failed = UInt8(2)
const _state_index = findfirst(==(:_state), fieldnames(Task))
@eval function load_state_acquire(t)
# TODO: Replace this by proper atomic operations when available
@GC.preserve t llvmcall($("""
%ptr = inttoptr i$(Sys.WORD_SIZE) %0 to i8*
%rv = load atomic i8, i8* %ptr acquire, align 8
ret i8 %rv
"""), UInt8, Tuple{Ptr{UInt8}},
Ptr{UInt8}(pointer_from_objref(t) + fieldoffset(Task, _state_index)))
end
@inline function getproperty(t::Task, field::Symbol)
if field === :state
# TODO: this field name should be deprecated in 2.0
st = load_state_acquire(t)
if st === task_state_runnable
return :runnable
elseif st === task_state_done
return :done
elseif st === task_state_failed
return :failed
else
@assert false
end
elseif field === :backtrace
# TODO: this field name should be deprecated in 2.0
return current_exceptions(t)[end][2]
elseif field === :exception
# TODO: this field name should be deprecated in 2.0
return t._isexception ? t.result : nothing
else
return getfield(t, field)
end
end
"""
istaskdone(t::Task) -> Bool
Determine whether a task has exited.
# Examples
```jldoctest
julia> a2() = sum(i for i in 1:1000);
julia> b = Task(a2);
julia> istaskdone(b)
false
julia> schedule(b);
julia> yield();
julia> istaskdone(b)
true
```
"""
istaskdone(t::Task) = load_state_acquire(t) !== task_state_runnable
"""
istaskstarted(t::Task) -> Bool
Determine whether a task has started executing.
# Examples
```jldoctest
julia> a3() = sum(i for i in 1:1000);
julia> b = Task(a3);
julia> istaskstarted(b)
false
```
"""
istaskstarted(t::Task) = ccall(:jl_is_task_started, Cint, (Any,), t) != 0
"""
istaskfailed(t::Task) -> Bool
Determine whether a task has exited because an exception was thrown.
# Examples
```jldoctest
julia> a4() = error("task failed");
julia> b = Task(a4);
julia> istaskfailed(b)
false
julia> schedule(b);
julia> yield();
julia> istaskfailed(b)
true
```
!!! compat "Julia 1.3"
This function requires at least Julia 1.3.
"""
istaskfailed(t::Task) = (load_state_acquire(t) === task_state_failed)
Threads.threadid(t::Task) = Int(ccall(:jl_get_task_tid, Int16, (Any,), t)+1)
function Threads.threadpool(t::Task)
tpid = ccall(:jl_get_task_threadpoolid, Int8, (Any,), t)
return Threads._tpid_to_sym(tpid)
end
task_result(t::Task) = t.result
task_local_storage() = get_task_tls(current_task())
function get_task_tls(t::Task)
if t.storage === nothing
t.storage = IdDict()
end
return (t.storage)::IdDict{Any,Any}
end
"""
task_local_storage(key)
Look up the value of a key in the current task's task-local storage.
"""
task_local_storage(key) = task_local_storage()[key]
"""
task_local_storage(key, value)
Assign a value to a key in the current task's task-local storage.
"""
task_local_storage(key, val) = (task_local_storage()[key] = val)
"""
task_local_storage(body, key, value)
Call the function `body` with a modified task-local storage, in which `value` is assigned to
`key`; the previous value of `key`, or lack thereof, is restored afterwards. Useful
for emulating dynamic scoping.
"""
function task_local_storage(body::Function, key, val)
tls = task_local_storage()
hadkey = haskey(tls, key)
old = get(tls, key, nothing)
tls[key] = val
try
return body()
finally
hadkey ? (tls[key] = old) : delete!(tls, key)
end
end
# just wait for a task to be done, no error propagation
function _wait(t::Task)
if !istaskdone(t)
donenotify = t.donenotify::ThreadSynchronizer
lock(donenotify)
try
while !istaskdone(t)
wait(donenotify)
end
finally
unlock(donenotify)
end
end
nothing
end
# have `waiter` wait for `t`
function _wait2(t::Task, waiter::Task)
if !istaskdone(t)
# since _wait2 is similar to schedule, we should observe the sticky
# bit, even if we don't call `schedule` with early-return below
if waiter.sticky && Threads.threadid(waiter) == 0 && !GC.in_finalizer()
# Issue #41324
# t.sticky && tid == 0 is a task that needs to be co-scheduled with
# the parent task. If the parent (current_task) is not sticky we must
# set it to be sticky.
# XXX: Ideally we would be able to unset this
current_task().sticky = true
tid = Threads.threadid()
ccall(:jl_set_task_tid, Cint, (Any, Cint), waiter, tid-1)
end
donenotify = t.donenotify::ThreadSynchronizer
lock(donenotify)
if !istaskdone(t)
push!(donenotify.waitq, waiter)
unlock(donenotify)
return nothing
else
unlock(donenotify)
end
end
schedule(waiter)
nothing
end
function wait(t::Task)
t === current_task() && error("deadlock detected: cannot wait on current task")
_wait(t)
if istaskfailed(t)
throw(TaskFailedException(t))
end
nothing
end
"""
fetch(x::Any)
Return `x`.
"""
fetch(@nospecialize x) = x
"""
fetch(t::Task)
Wait for a [`Task`](@ref) to finish, then return its result value.
If the task fails with an exception, a [`TaskFailedException`](@ref) (which wraps the failed task)
is thrown.
"""
function fetch(t::Task)
wait(t)
return task_result(t)
end
## lexically-scoped waiting for multiple items
struct ScheduledAfterSyncException <: Exception
values::Vector{Any}
end
function showerror(io::IO, ex::ScheduledAfterSyncException)
print(io, "ScheduledAfterSyncException: ")
if isempty(ex.values)
print(io, "(no values)")
return
end
show(io, ex.values[1])
if length(ex.values) == 1
print(io, " is")
elseif length(ex.values) == 2
print(io, " and one more ")
print(io, nameof(typeof(ex.values[2])))
print(io, " are")
else
print(io, " and ", length(ex.values) - 1, " more objects are")
end
print(io, " registered after the end of a `@sync` block")
end
function sync_end(c::Channel{Any})
local c_ex
while isready(c)
r = take!(c)
if isa(r, Task)
_wait(r)
if istaskfailed(r)
if !@isdefined(c_ex)
c_ex = CompositeException()
end
push!(c_ex, TaskFailedException(r))
end
else
try
wait(r)
catch e
if !@isdefined(c_ex)
c_ex = CompositeException()
end
push!(c_ex, e)
end
end
end
close(c)
# Capture all waitable objects scheduled after the end of `@sync` and
# include them in the exception. This way, the user can check what was
# scheduled by examining at the exception object.
if isready(c)
local racy
for r in c
if !@isdefined(racy)
racy = []
end
push!(racy, r)
end
if @isdefined(racy)
if !@isdefined(c_ex)
c_ex = CompositeException()
end
# Since this is a clear programming error, show this exception first:
pushfirst!(c_ex, ScheduledAfterSyncException(racy))
end
end
if @isdefined(c_ex)
throw(c_ex)
end
nothing
end
const sync_varname = gensym(:sync)
"""
@sync
Wait until all lexically-enclosed uses of [`@async`](@ref), [`@spawn`](@ref Threads.@spawn),
`Distributed.@spawnat` and `Distributed.@distributed`
are complete. All exceptions thrown by enclosed async operations are collected and thrown as
a [`CompositeException`](@ref).
# Examples
```julia-repl
julia> Threads.nthreads()
4
julia> @sync begin
Threads.@spawn println("Thread-id \$(Threads.threadid()), task 1")
Threads.@spawn println("Thread-id \$(Threads.threadid()), task 2")
end;
Thread-id 3, task 1
Thread-id 1, task 2
```
"""
macro sync(block)
var = esc(sync_varname)
quote
let $var = Channel(Inf)
v = $(esc(block))
sync_end($var)
v
end
end
end
# schedule an expression to run asynchronously
"""
@async
Wrap an expression in a [`Task`](@ref) and add it to the local machine's scheduler queue.
Values can be interpolated into `@async` via `\$`, which copies the value directly into the
constructed underlying closure. This allows you to insert the _value_ of a variable,
isolating the asynchronous code from changes to the variable's value in the current task.
!!! warning
It is strongly encouraged to favor `Threads.@spawn` over `@async` always **even when no
parallelism is required** especially in publicly distributed libraries. This is
because a use of `@async` disables the migration of the *parent* task across worker
threads in the current implementation of Julia. Thus, seemingly innocent use of
`@async` in a library function can have a large impact on the performance of very
different parts of user applications.
!!! compat "Julia 1.4"
Interpolating values via `\$` is available as of Julia 1.4.
"""
macro async(expr)
do_async_macro(expr, __source__)
end
# generate the code for @async, possibly wrapping the task in something before
# pushing it to the wait queue.
function do_async_macro(expr, linenums; wrap=identity)
letargs = Base._lift_one_interp!(expr)
thunk = Base.replace_linenums!(:(()->($(esc(expr)))), linenums)
var = esc(sync_varname)
quote
let $(letargs...)
local task = Task($thunk)
if $(Expr(:islocal, var))
put!($var, $(wrap(:task)))
end
schedule(task)
task
end
end
end
# task wrapper that doesn't create exceptions wrapped in TaskFailedException
struct UnwrapTaskFailedException <: Exception
task::Task
end
# common code for wait&fetch for UnwrapTaskFailedException
function unwrap_task_failed(f::Function, t::UnwrapTaskFailedException)
try
f(t.task)
catch ex
if ex isa TaskFailedException
throw(ex.task.exception)
else
rethrow()
end
end
end
# the unwrapping for above task wrapper (gets triggered in sync_end())
wait(t::UnwrapTaskFailedException) = unwrap_task_failed(wait, t)
# same for fetching the tasks, for convenience
fetch(t::UnwrapTaskFailedException) = unwrap_task_failed(fetch, t)
# macro for running async code that doesn't throw wrapped exceptions
macro async_unwrap(expr)
do_async_macro(expr, __source__, wrap=task->:(Base.UnwrapTaskFailedException($task)))
end
"""
errormonitor(t::Task)
Print an error log to `stderr` if task `t` fails.
# Examples
```julia-repl
julia> Base._wait(errormonitor(Threads.@spawn error("task failed")))
Unhandled Task ERROR: task failed
Stacktrace:
[...]
```
"""
function errormonitor(t::Task)
t2 = Task() do
if istaskfailed(t)
local errs = stderr
try # try to display the failure atomically
errio = IOContext(PipeBuffer(), errs::IO)
emphasize(errio, "Unhandled Task ")
display_error(errio, scrub_repl_backtrace(current_exceptions(t)))
write(errs, errio)
catch
try # try to display the secondary error atomically
errio = IOContext(PipeBuffer(), errs::IO)
print(errio, "\nSYSTEM: caught exception while trying to print a failed Task notice: ")
display_error(errio, scrub_repl_backtrace(current_exceptions()))
write(errs, errio)
flush(errs)
# and then the actual error, as best we can
Core.print(Core.stderr, "while handling: ")
Core.println(Core.stderr, current_exceptions(t)[end][1])
catch e
# give up
Core.print(Core.stderr, "\nSYSTEM: caught exception of type ", typeof(e).name.name,
" while trying to print a failed Task notice; giving up\n")
end
end
end
nothing
end
t2.sticky = false
_wait2(t, t2)
return t
end
# Capture interpolated variables in $() and move them to let-block
function _lift_one_interp!(e)
letargs = Any[] # store the new gensymed arguments
_lift_one_interp_helper(e, false, letargs) # Start out _not_ in a quote context (false)
letargs
end
_lift_one_interp_helper(v, _, _) = v
function _lift_one_interp_helper(expr::Expr, in_quote_context, letargs)
if expr.head === :$
if in_quote_context # This $ is simply interpolating out of the quote
# Now, we're out of the quote, so any _further_ $ is ours.
in_quote_context = false
else
newarg = gensym()
push!(letargs, :($(esc(newarg)) = $(esc(expr.args[1]))))
return newarg # Don't recurse into the lifted $() exprs
end
elseif expr.head === :quote
in_quote_context = true # Don't try to lift $ directly out of quotes
elseif expr.head === :macrocall
return expr # Don't recur into macro calls, since some other macros use $
end
for (i,e) in enumerate(expr.args)
expr.args[i] = _lift_one_interp_helper(e, in_quote_context, letargs)
end
expr
end
# add a wait-able object to the sync pool
macro sync_add(expr)
var = esc(sync_varname)
quote
local ref = $(esc(expr))
put!($var, ref)
ref
end
end
# runtime system hook called when a task finishes
function task_done_hook(t::Task)
# `finish_task` sets `sigatomic` before entering this function
err = istaskfailed(t)
result = task_result(t)
handled = false
donenotify = t.donenotify
if isa(donenotify, ThreadSynchronizer)
lock(donenotify)
try
if !isempty(donenotify.waitq)
handled = true
notify(donenotify)
end
finally
unlock(donenotify)
end
end
if err && !handled && Threads.threadid() == 1
if isa(result, InterruptException) && isdefined(Base, :active_repl_backend) &&
active_repl_backend.backend_task._state === task_state_runnable && isempty(Workqueue) &&
active_repl_backend.in_eval
throwto(active_repl_backend.backend_task, result) # this terminates the task
end
end
# Clear sigatomic before waiting
sigatomic_end()
try
wait() # this will not return
catch e
# If an InterruptException happens while blocked in the event loop, try handing
# the exception to the REPL task since the current task is done.
# issue #19467
if Threads.threadid() == 1 &&
isa(e, InterruptException) && isdefined(Base, :active_repl_backend) &&
active_repl_backend.backend_task._state === task_state_runnable && isempty(Workqueue) &&
active_repl_backend.in_eval
throwto(active_repl_backend.backend_task, e)
else
rethrow()
end
end
end
## scheduler and work queue
mutable struct IntrusiveLinkedListSynchronized{T}
queue::IntrusiveLinkedList{T}
lock::Threads.SpinLock
IntrusiveLinkedListSynchronized{T}() where {T} = new(IntrusiveLinkedList{T}(), Threads.SpinLock())
end
isempty(W::IntrusiveLinkedListSynchronized) = isempty(W.queue)
length(W::IntrusiveLinkedListSynchronized) = length(W.queue)
function push!(W::IntrusiveLinkedListSynchronized{T}, t::T) where T
lock(W.lock)
try
push!(W.queue, t)
finally
unlock(W.lock)
end
return W
end
function pushfirst!(W::IntrusiveLinkedListSynchronized{T}, t::T) where T
lock(W.lock)
try
pushfirst!(W.queue, t)
finally
unlock(W.lock)
end
return W
end
function pop!(W::IntrusiveLinkedListSynchronized)
lock(W.lock)
try
return pop!(W.queue)
finally
unlock(W.lock)
end
end
function popfirst!(W::IntrusiveLinkedListSynchronized)
lock(W.lock)
try
return popfirst!(W.queue)
finally
unlock(W.lock)
end
end
function list_deletefirst!(W::IntrusiveLinkedListSynchronized{T}, t::T) where T
lock(W.lock)
try
list_deletefirst!(W.queue, t)
finally
unlock(W.lock)
end
return W
end
const StickyWorkqueue = IntrusiveLinkedListSynchronized{Task}
global Workqueues::Vector{StickyWorkqueue} = [StickyWorkqueue()]
const Workqueues_lock = Threads.SpinLock()
const Workqueue = Workqueues[1] # default work queue is thread 1 // TODO: deprecate this variable
function workqueue_for(tid::Int)
qs = Workqueues
if length(qs) >= tid && isassigned(qs, tid)
return @inbounds qs[tid]
end
# slow path to allocate it
@assert tid > 0
l = Workqueues_lock
@lock l begin
qs = Workqueues
if length(qs) < tid
nt = Threads.maxthreadid()
@assert tid <= nt
global Workqueues = qs = copyto!(typeof(qs)(undef, length(qs) + nt - 1), qs)
end
if !isassigned(qs, tid)
@inbounds qs[tid] = StickyWorkqueue()
end
return @inbounds qs[tid]
end
end
function enq_work(t::Task)
(t._state === task_state_runnable && t.queue === nothing) || error("schedule: Task not runnable")
# Sticky tasks go into their thread's work queue.
if t.sticky
tid = Threads.threadid(t)
if tid == 0
# The task is not yet stuck to a thread. Stick it to the current
# thread and do the same to the parent task (the current task) so
# that the tasks are correctly co-scheduled (issue #41324).
# XXX: Ideally we would be able to unset this.
if GC.in_finalizer()
# The task was launched in a finalizer. There is no thread to sticky it
# to, so just allow it to run anywhere as if it had been non-sticky.
t.sticky = false
@goto not_sticky
else
tid = Threads.threadid()
ccall(:jl_set_task_tid, Cint, (Any, Cint), t, tid-1)
current_task().sticky = true
end
end
push!(workqueue_for(tid), t)
else
@label not_sticky
tp = Threads.threadpool(t)
if tp === :foreign || Threads.threadpoolsize(tp) == 1
# There's only one thread in the task's assigned thread pool;
# use its work queue.
tid = (tp === :interactive) ? 1 : Threads.threadpoolsize(:interactive)+1
ccall(:jl_set_task_tid, Cint, (Any, Cint), t, tid-1)
push!(workqueue_for(tid), t)
else
# Otherwise, put the task in the multiqueue.
Partr.multiq_insert(t, t.priority)
tid = 0
end
end
ccall(:jl_wakeup_thread, Cvoid, (Int16,), (tid - 1) % Int16)
return t
end
schedule(t::Task) = enq_work(t)
"""
schedule(t::Task, [val]; error=false)
Add a [`Task`](@ref) to the scheduler's queue. This causes the task to run constantly when the system
is otherwise idle, unless the task performs a blocking operation such as [`wait`](@ref).
If a second argument `val` is provided, it will be passed to the task (via the return value of
[`yieldto`](@ref)) when it runs again. If `error` is `true`, the value is raised as an exception in
the woken task.
!!! warning
It is incorrect to use `schedule` on an arbitrary `Task` that has already been started.
See [the API reference](@ref low-level-schedule-wait) for more information.
# Examples
```jldoctest
julia> a5() = sum(i for i in 1:1000);
julia> b = Task(a5);
julia> istaskstarted(b)
false
julia> schedule(b);
julia> yield();
julia> istaskstarted(b)
true
julia> istaskdone(b)
true
```
"""
function schedule(t::Task, @nospecialize(arg); error=false)
# schedule a task to be (re)started with the given value or exception
t._state === task_state_runnable || Base.error("schedule: Task not runnable")
if error
t.queue === nothing || Base.list_deletefirst!(t.queue::IntrusiveLinkedList{Task}, t)
setfield!(t, :result, arg)
setfield!(t, :_isexception, true)
else
t.queue === nothing || Base.error("schedule: Task not runnable")
setfield!(t, :result, arg)
end
enq_work(t)
return t
end
"""
yield()
Switch to the scheduler to allow another scheduled task to run. A task that calls this
function is still runnable, and will be restarted immediately if there are no other runnable
tasks.
"""
function yield()
ct = current_task()
enq_work(ct)
try
wait()
catch
ct.queue === nothing || list_deletefirst!(ct.queue::IntrusiveLinkedList{Task}, ct)
rethrow()
end
end
@inline set_next_task(t::Task) = ccall(:jl_set_next_task, Cvoid, (Any,), t)
"""
yield(t::Task, arg = nothing)
A fast, unfair-scheduling version of `schedule(t, arg); yield()` which
immediately yields to `t` before calling the scheduler.
"""
function yield(t::Task, @nospecialize(x=nothing))
(t._state === task_state_runnable && t.queue === nothing) || error("yield: Task not runnable")
t.result = x
enq_work(current_task())
set_next_task(t)
return try_yieldto(ensure_rescheduled)
end
"""
yieldto(t::Task, arg = nothing)
Switch to the given task. The first time a task is switched to, the task's function is
called with no arguments. On subsequent switches, `arg` is returned from the task's last
call to `yieldto`. This is a low-level call that only switches tasks, not considering states
or scheduling in any way. Its use is discouraged.
"""
function yieldto(t::Task, @nospecialize(x=nothing))
# TODO: these are legacy behaviors; these should perhaps be a scheduler
# state error instead.
if t._state === task_state_done
return x
elseif t._state === task_state_failed
throw(t.result)
end
t.result = x
set_next_task(t)
return try_yieldto(identity)
end
function try_yieldto(undo)
try
ccall(:jl_switch, Cvoid, ())
catch
undo(ccall(:jl_get_next_task, Ref{Task}, ()))
rethrow()
end
ct = current_task()
if ct._isexception
exc = ct.result
ct.result = nothing
ct._isexception = false
throw(exc)
end
result = ct.result
ct.result = nothing
return result
end
# yield to a task, throwing an exception in it
function throwto(t::Task, @nospecialize exc)
t.result = exc
t._isexception = true
set_next_task(t)
return try_yieldto(identity)
end
function ensure_rescheduled(othertask::Task)
ct = current_task()
W = workqueue_for(Threads.threadid())
if ct !== othertask && othertask._state === task_state_runnable
# we failed to yield to othertask
# return it to the head of a queue to be retried later
tid = Threads.threadid(othertask)
Wother = tid == 0 ? W : workqueue_for(tid)
pushfirst!(Wother, othertask)
end
# if the current task was queued,
# also need to return it to the runnable state
# before throwing an error
list_deletefirst!(W, ct)
nothing
end
function trypoptask(W::StickyWorkqueue)
while !isempty(W)
t = popfirst!(W)
if t._state !== task_state_runnable
# assume this somehow got queued twice,
# probably broken now, but try discarding this switch and keep going
# can't throw here, because it's probably not the fault of the caller to wait
# and don't want to use print() here, because that may try to incur a task switch
ccall(:jl_safe_printf, Cvoid, (Ptr{UInt8}, Int32...),
"\nWARNING: Workqueue inconsistency detected: popfirst!(Workqueue).state !== :runnable\n")
continue
end
return t
end
return Partr.multiq_deletemin()
end
checktaskempty = Partr.multiq_check_empty
@noinline function poptask(W::StickyWorkqueue)
task = trypoptask(W)
if !(task isa Task)
task = ccall(:jl_task_get_next, Ref{Task}, (Any, Any, Any), trypoptask, W, checktaskempty)
end
set_next_task(task)
nothing
end
function wait()
GC.safepoint()
W = workqueue_for(Threads.threadid())
poptask(W)
result = try_yieldto(ensure_rescheduled)
process_events()