SERVER-35612 Implement ChunkWritesTracker with unit tests, make ChunkInfo use it

1 files changed, 99 insertions, 0 deletions

diff --git a/src/mongo/s/chunk_writes_tracker.h b/src/mongo/s/chunk_writes_tracker.h
new file mode 100644
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+++ b/src/mongo/s/chunk_writes_tracker.h
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+/**
+ *    Copyright (C) 2018 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    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 Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/platform/atomic_word.h"
+#include "mongo/stdx/mutex.h"
+
+namespace mongo {
+
+class ChunkWritesTracker {
+public:
+    /**
+     * A factor that determines when a chunk should be split. We should split once data *
+     * kSplitTestFactor > chunkSize (approximately).
+     */
+    static constexpr uint64_t kSplitTestFactor = 5;
+
+    /**
+     * Add more bytes written to the chunk.
+     */
+    void addBytesWritten(uint64_t bytesWritten) {
+        _bytesWritten.fetchAndAdd(bytesWritten);
+    }
+
+    /**
+     * Returns the total number of bytes that have been written to the chunk.
+     */
+    uint64_t getBytesWritten() {
+        return _bytesWritten.loadRelaxed();
+    }
+
+    /**
+     * Sets the number of bytes in the tracker to zero.
+     */
+    void clearBytesWritten();
+
+    /**
+     * Returns whether or not this chunk is ready to be split based on the
+     * maximum allowable size of a chunk.
+     */
+    bool shouldSplit(uint64_t maxChunkSize);
+
+    /**
+     * Locks the chunk for splitting, returning false if it is already locked.
+     * While it is locked, shouldSplit will always return false.
+     */
+    bool acquireSplitLock();
+
+    /**
+     * Releases the lock acquired for splitting.
+     */
+    void releaseSplitLock();
+
+private:
+    /**
+     * The number of bytes that have been written to this chunk. May be
+     * modified concurrently by several threads.
+     */
+    AtomicUInt64 _bytesWritten{0};
+
+    /**
+     * Protects _splitState when starting a split.
+     */
+    stdx::mutex _mtx;
+
+    /**
+     * Whether or not a current split is in progress for this chunk.
+     */
+    bool _isLockedForSplitting{false};
+};
+
+}  // namespace mongo