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+/* Synchronized work queue.
+
+ Copyright (C) 2025 Free Software Foundation, Inc.
+
+ This file is part of GDB.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+#ifndef GDBSUPPORT_WORK_QUEUE_H
+#define GDBSUPPORT_WORK_QUEUE_H
+
+#include "gdbsupport/iterator-range.h"
+
+namespace gdb
+{
+
+/* Implementation of a thread-safe work queue.
+
+ The work items are specified by two iterators of type RandomIt.
+
+ BATCH_SIZE is the number of work items to pop in a batch. */
+
+template<typename RandomIt, std::size_t batch_size>
+class work_queue
+{
+public:
+ /* The work items are specified by the range `[first, last[`. */
+ work_queue (const RandomIt first, const RandomIt last) noexcept
+ : m_next (first),
+ m_last (last)
+ {
+ gdb_assert (first <= last);
+ }
+
+ DISABLE_COPY_AND_ASSIGN (work_queue);
+
+ /* Pop a batch of work items.
+
+ The return value is an iterator range delimiting the work items. */
+ iterator_range<RandomIt> pop_batch () noexcept
+ {
+ for (;;)
+ {
+ /* Grab a snapshot of M_NEXT. */
+ auto next = m_next.load ();
+ gdb_assert (next <= m_last);
+
+ /* The number of items remaining in the queue. */
+ const auto n_remaining = static_cast<std::size_t> (m_last - next);
+
+ /* Are we done? */
+ if (n_remaining == 0)
+ return { m_last, m_last };
+
+ /* The batch size is proportional to the number of items remaining in
+ the queue. We do this to try to stike a balance, avoiding
+ synchronization overhead when there are many items to process at the
+ start, and avoiding workload imbalance when there are few items to
+ process at the end. */
+ const auto this_batch_size = std::min (batch_size, n_remaining);
+
+ /* The range of items in this batch. */
+ const auto this_batch_first = next;
+ const auto this_batch_last = next + this_batch_size;
+
+ /* Update M_NEXT. If the current value of M_NEXT doesn't match NEXT, it
+ means another thread updated it concurrently, restart. */
+ if (!m_next.compare_exchange_weak (next, this_batch_last))
+ continue;
+
+ return { this_batch_first, this_batch_last };
+ }
+ }
+
+private:
+ /* The next work item to hand out. */
+ std::atomic<RandomIt> m_next;
+
+ /* The end of the work item range. */
+ RandomIt m_last;
+};
+
+} /* namespace gdb */
+
+#endif /* GDBSUPPORT_WORK_QUEUE_H */