SERVER-30748 WithLock to replace _inlock

1 files changed, 98 insertions, 0 deletions

diff --git a/src/mongo/util/concurrency/with_lock.h b/src/mongo/util/concurrency/with_lock.h
new file mode 100644
index 00000000000..d26c675e293
--- /dev/null
+++ b/src/mongo/util/concurrency/with_lock.h
@@ -0,0 +1,98 @@
+/**    Copyright 2017 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/stdx/mutex.h"
+#include "mongo/util/invariant.h"
+
+#include <utility>
+
+namespace mongo {
+
+/**
+ * WithLock is an attestion to pass as an argument to functions that must be called only while
+ * holding a lock, as a rigorous alternative to an unchecked naming convention and/or stern
+ * comments.  It helps prevent a common usage error.
+ *
+ * It may be used to modernize code from (something like) this
+ *
+ *     // Member _mutex MUST be held when calling this:
+ *     void _clobber_inlock(OperationContext* opCtx) {
+ *         _stuff = makeStuff(opCtx);
+ *     }
+ *
+ * into
+ *
+ *     void _clobber(WithLock, OperationContext* opCtx) {
+ *         _stuff = makeStuff(opCtx);
+ *     }
+ *
+ * A call to such a function looks like this:
+ *
+ *     stdx::lock_guard<stdx::mutex> lk(_mutex);
+ *     _clobber(lk, opCtx);  // instead of _clobber_inlock(opCtx)
+ *
+ * Note that the formal argument need not (and should not) be named unless it is needed to pass
+ * the attestation along to another function:
+ *
+ *     void _clobber(WithLock lock, OperationContext* opCtx) {
+ *         _really_clobber(lock, opCtx);
+ *     }
+ *
+ */
+struct WithLock {
+    template <typename Mutex>
+    WithLock(stdx::lock_guard<Mutex> const&) noexcept {}
+
+    template <typename Mutex>
+    WithLock(stdx::unique_lock<Mutex> const& lock) noexcept {
+        invariant(lock.owns_lock());
+    }
+
+    // Pass by value is OK.
+    WithLock(WithLock const&) noexcept {}
+    WithLock(WithLock&&) noexcept {}
+
+    WithLock() = delete;
+
+    // No assigning WithLocks.
+    void operator=(WithLock const&) = delete;
+    void operator=(WithLock&&) = delete;
+
+    // No accidentally moving a unique_lock<> in.
+    template <typename Mutex>
+    WithLock(stdx::unique_lock<Mutex>&&) = delete;
+};
+
+}  // namespace mongo
+
+namespace std {
+// No moving a WithLock:
+template <>
+mongo::WithLock&& move<mongo::WithLock>(mongo::WithLock&&) = delete;
+}  // namespace std