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Assert try_enqueue does not move-from callable on failure

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enqueue_work_autoscale relies on BoundedQueue::try_enqueue leaving the
callable untouched when the semaphore check fails.  This is correct
today because tryWait() is evaluated before std::forward moves the
item, but the coupling is implicit — a future BoundedQueue change
that reorders these operations would silently introduce a use-after-
move bug on the blocking fallback path.

Add a debug assert after the failed try_enqueue to verify the Func is
still valid before using it on the blocking path.  Strengthen the
comment to explicitly name the invariant being relied upon.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Antonio S. Musumeci 2026-04-10 12:40:43 -04:00
parent ea47934c63
commit 4d35726fc6
1 changed files with 13 additions and 3 deletions
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16
vendored/libfuse/include/thread_pool.hpp
View file

@ -24,6 +24,7 @@
#include "mutex.hpp"
#include <algorithm>
#include <cassert>
#include <atomic>
#include <cerrno>
#include <csignal>
@ -955,8 +956,11 @@ ThreadPool::enqueue_work_autoscale(ThreadPool::PToken &ptok_,
// Materialize into a Func up front so we own the value across
// the try/block-enqueue boundary without a double std::forward.
//
// Safe: BoundedQueue::try_enqueue checks the semaphore before
// forwarding, so f is not moved-from on failure.
// INVARIANT: BoundedQueue::try_enqueue checks the semaphore
// (tryWait) *before* forwarding the item into the inner queue.
// On failure the item is never moved-from, so f remains valid.
// The assert below guards against future BoundedQueue changes
// that could violate this ordering.
Func f(std::forward<FuncType>(func_));
if(_queue.try_enqueue(std::move(f)))
@ -965,6 +969,9 @@ ThreadPool::enqueue_work_autoscale(ThreadPool::PToken &ptok_,
return;
}
assert(static_cast<bool>(f) &&
"BoundedQueue::try_enqueue moved the callable despite returning false");
_maybe_grow_on_pressure();
// Block-enqueue (will succeed once a worker frees a slot)
@ -978,7 +985,7 @@ inline
void
ThreadPool::enqueue_work_autoscale(FuncType &&func_)
{
// See ptok_ overload for safety note on try_enqueue + move.
// See ptok_ overload for invariant and safety note.
Func f(std::forward<FuncType>(func_));
if(_queue.try_enqueue(std::move(f)))
@ -987,6 +994,9 @@ ThreadPool::enqueue_work_autoscale(FuncType &&func_)
return;
}
assert(static_cast<bool>(f) &&
"BoundedQueue::try_enqueue moved the callable despite returning false");
_maybe_grow_on_pressure();
// Block-enqueue (will succeed once a worker frees a slot)