SERVER-43324 Add BasicLockableAdaptor for cleaner function APIs

1 files changed, 74 insertions, 0 deletions

diff --git a/src/mongo/util/lockable_adapter.h b/src/mongo/util/lockable_adapter.h
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+++ b/src/mongo/util/lockable_adapter.h
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+/**
+ *    Copyright (C) 2019-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    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
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    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 Server Side 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
+
+namespace mongo {
+
+// BasicLockableAdapter allows non-template functions to take any lockable type. This can be useful
+// when you have a custom lockable type and don't want to make the lockable parameter concrete for a
+// function but can't make the function use a template parameter for the lock type.
+//
+// This type should NOT be used to store a lockable type!
+//
+// Example:
+//      void wait(BasicLockableAdapter lock) {
+//          stdx::lock_guard lg(lock);
+//      }
+//
+//      mongo::ResourceMutex mut;
+//      wait(mut);
+class BasicLockableAdapter {
+public:
+    template <typename T>
+    BasicLockableAdapter(T& lock) : _underlyingLock(&lock), _vtable(&forT<std::decay_t<T>>) {}
+
+    void lock() {
+        _vtable->lock(_underlyingLock);
+    }
+
+    void unlock() {
+        _vtable->unlock(_underlyingLock);
+    }
+
+private:
+    struct VTable {
+        void (*lock)(void*);
+        void (*unlock)(void*);
+    };
+
+    template <typename T>
+    static inline VTable forT = VTable{+[](void* t) { static_cast<T*>(t)->lock(); },
+                                       +[](void* t) { static_cast<T*>(t)->unlock(); }};
+
+    void* _underlyingLock;
+    const VTable* _vtable;
+};
+
+}  // namespace mongo