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Scheduler: do not always switch to the scheduler task #58765

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Scheduler: do not always switch to the scheduler task #58765

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7932bde
Scheduler: do not always switch to the scheduler task
kpamnany Jun 17, 2025
0aceda7
Incorporate review suggestion
kpamnany Jun 23, 2025
49a9749
Set task's `start`/`code` field to `nothing`
kpamnany Jun 23, 2025
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22 changes: 7 additions & 15 deletions base/task.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -1145,16 +1145,6 @@ function throwto(t::Task, @nospecialize exc)
return try_yieldto(identity)
end

@inline function wait_forever()
while true
wait()
end
end

const get_sched_task = OncePerThread{Task}() do
Task(wait_forever)
end

function ensure_rescheduled(othertask::Task)
ct = current_task()
W = workqueue_for(Threads.threadid())
Expand Down Expand Up @@ -1204,11 +1194,13 @@ function wait()
W = workqueue_for(Threads.threadid())
task = trypoptask(W)
if task === nothing
# No tasks to run; switch to the scheduler task to run the
# thread sleep logic.
sched_task = get_sched_task()
if ct !== sched_task
return yieldto(sched_task)
# No tasks to run; if the current task is done/failed, switch to an
# empty "scheduler" task to run the thread sleep logic.
if istaskdone(ct)
scheduler_task() = nothing
if ct.code !== scheduler_task
return yieldto(Task(scheduler_task))
end
end
task = ccall(:jl_task_get_next, Ref{Task}, (Any, Any, Any), trypoptask, W, checktaskempty)
end
Expand Down
2 changes: 1 addition & 1 deletion src/task.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1568,7 +1568,7 @@ jl_task_t *jl_init_root_task(jl_ptls_t ptls, void *stack_lo, void *stack_hi)
ct->queue = jl_nothing;
ct->tls = jl_nothing;
jl_atomic_store_relaxed(&ct->_state, JL_TASK_STATE_RUNNABLE);
ct->start = NULL;
ct->start = jl_nothing;
ct->result = jl_nothing;
ct->donenotify = jl_nothing;
jl_atomic_store_relaxed(&ct->_isexception, 0);
Expand Down