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20e3867ad8
In preparation for a following patch that will re-use the shared work queue algorithm, move it to a separate class. Change-Id: Id05cf8898a5d162048fa8fa056fbf7e0441bfb78 Approved-By: Tom Tromey <tom@tromey.com>
97 lines
2.8 KiB
C++
97 lines
2.8 KiB
C++
/* Synchronized work queue.
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Copyright (C) 2025 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef GDBSUPPORT_WORK_QUEUE_H
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#define GDBSUPPORT_WORK_QUEUE_H
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#include "gdbsupport/iterator-range.h"
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namespace gdb
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{
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/* Implementation of a thread-safe work queue.
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The work items are specified by two iterators of type RandomIt.
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BATCH_SIZE is the number of work items to pop in a batch. */
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template<typename RandomIt, std::size_t batch_size>
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class work_queue
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{
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public:
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/* The work items are specified by the range `[first, last[`. */
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work_queue (const RandomIt first, const RandomIt last) noexcept
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: m_next (first),
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m_last (last)
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{
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gdb_assert (first <= last);
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}
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DISABLE_COPY_AND_ASSIGN (work_queue);
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/* Pop a batch of work items.
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The return value is an iterator range delimiting the work items. */
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iterator_range<RandomIt> pop_batch () noexcept
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{
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for (;;)
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{
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/* Grab a snapshot of M_NEXT. */
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auto next = m_next.load ();
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gdb_assert (next <= m_last);
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/* The number of items remaining in the queue. */
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const auto n_remaining = static_cast<std::size_t> (m_last - next);
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/* Are we done? */
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if (n_remaining == 0)
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return { m_last, m_last };
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/* The batch size is proportional to the number of items remaining in
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the queue. We do this to try to stike a balance, avoiding
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synchronization overhead when there are many items to process at the
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start, and avoiding workload imbalance when there are few items to
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process at the end. */
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const auto this_batch_size = std::min (batch_size, n_remaining);
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/* The range of items in this batch. */
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const auto this_batch_first = next;
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const auto this_batch_last = next + this_batch_size;
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/* Update M_NEXT. If the current value of M_NEXT doesn't match NEXT, it
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means another thread updated it concurrently, restart. */
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if (!m_next.compare_exchange_weak (next, this_batch_last))
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continue;
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return { this_batch_first, this_batch_last };
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}
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}
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private:
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/* The next work item to hand out. */
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std::atomic<RandomIt> m_next;
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/* The end of the work item range. */
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RandomIt m_last;
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};
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} /* namespace gdb */
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#endif /* GDBSUPPORT_WORK_QUEUE_H */
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