Default to 1 interactive thread #57087

IanButterworth · 2025-01-17T20:28:40Z

Part of #43672

So:

default == 1 default, 1 interactive
-t1 == 1 default, 1 interactive
-t1,0 == 1 default, 0 interactive
etc.

Motivations

Means the IO loop isn't on the worker threadpool (unless interactive threadpool is set to 0)
Allows the REPL to do threaded things in the background i.e.
- completion hints that could be cancelled on next keystroke
- Pkg loads in the background so user can type immediately in the pkg repl

Todo

Docs & News
- Make it clear that the repl operates in the :interactive threadpool, and that a bare @spawn or @threads will schedule in the :default threadpool
- Cover that the IO loop by default now runs in a different thread to operations
- Explain how to disable it. i.e. -t1,0
- Explain no :interactive threadpool during precompilation/PackageCompiler

Issues

Test and fix Distributed when threads are enabled (Many fixes and Distributed is now tested on its own CI with -t4,4 to shake issues out) 🤖 [master] Bump the Distributed stdlib from c613685 to 8890288 #57169

src/jloptions.c

IanButterworth · 2025-01-18T22:18:55Z

test/threads_exec.jl

-function test_thread_range()
-    a = zeros(Int, threadpoolsize())
-    @threads for i in 1:threadid()
-        a[i] = 1
-    end
-    for i in 1:threadid()
-        @test a[i] == 1
-    end
-    for i in (threadid() + 1):threadpoolsize()
-        @test a[i] == 0
-    end
-end
-test_thread_range()
-


I couldn't figure out what this test is actually testing, given the test script always runs from thread 1

IanButterworth · 2025-01-20T04:17:04Z

doc/src/manual/methods.md

@@ -614,7 +614,7 @@ Start some other operations that use `f(x)`:
 julia> g(x) = f(x)
 g (generic function with 1 method)

-julia> t = Threads.@spawn f(wait()); yield();
+julia> t = @async f(wait()); yield();


These were changed to @spawn in #55315 but I think they make sense as @async otherwise more orchestration is needed when multiple threads are available to make the examples work as expected.

IanButterworth · 2025-01-20T19:45:26Z

test/gcext/gcext.c

+    // single threaded mode
+    // Note: with -t1,1 a signal 10 occurs in task_scanner
+    jl_options.nthreadpools = 1;
+    jl_options.nthreads = 1;
+    int16_t ntpp[] = {jl_options.nthreads};
+    jl_options.nthreads_per_pool = ntpp;


Could the signal 10 be related to/fixed by #56477 ?

IanButterworth · 2025-01-27T19:58:09Z

Building on @JamesWrigley's work we've done a push to more extensively test and fix Distributed's thread safety, including running its own tests with -t4,4 and enabling tests that were previously disabled when multithreading, which shook out issues that are now fixed #57169 There's room for improvement (moving away from @async to avoid races) but the situation seems evidently good now based on testing.

I believe that was the only blocking issue here?

fix test thread indexing make threads_exec work being called from :interactive and :default pools add tests for threaded construct default pools etc.

I believe these make more sense as async than spawn, otherwise more orchestration is needed in the example. Were changed to spawn in JuliaLang#55315

IanButterworth added the multithreading Base.Threads and related functionality label Jan 17, 2025

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Test startup with multithreads and no sysimage #57099

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Make excluded threadunsafe tests threadsafe JuliaLang/Distributed.jl#121

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default to 1 interactive thread, or 0 if generating output

87224c3

un-doctest examples that aren't guaranteed threaded output order

e922afd

hide unstable channel show in doctests

def3e06

expand threads_exec tests to cover interactive threads

5a677d4

fix test thread indexing make threads_exec work being called from :interactive and :default pools add tests for threaded construct default pools etc.

use isempty so failing test shows content

731c4e8

run gcext test single threaded

040532f

delete unclear test

96bbd3c

IanButterworth added 4 commits January 27, 2025 14:58

REPL: fix brittle replcompletions test

a895fa8

revert doc examples to @async

47cd776

I believe these make more sense as async than spawn, otherwise more orchestration is needed in the example. Were changed to spawn in JuliaLang#55315

add News

4b1c78b

update docs

eb92c57

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IanButterworth merged commit fbe8656 into JuliaLang:master Jan 28, 2025
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jmkuhn mentioned this pull request Jan 28, 2025

use per-task (not per-thread) flags, rounding mode, etcetera? JuliaMath/DecFP.jl#153

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JamesWrigley mentioned this pull request Jan 29, 2025

Segmentation fault with threaded Distributed JuliaPy/PythonCall.jl#572

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Segfault during boot with --sysimage-native-code=no while multithreaded #57198

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Default to 1 interactive thread #57087

Default to 1 interactive thread #57087

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Default to 1 interactive thread #57087

Default to 1 interactive thread #57087

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Motivations

Todo

Issues

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