Move MonitoredRefCount and RetainGuard to vespalib.

4 files changed, 119 insertions, 0 deletions

diff --git a/vespalib/src/vespa/vespalib/util/CMakeLists.txt b/vespalib/src/vespa/vespalib/util/CMakeLists.txt
index 9e2917775f0..6115c21623d 100644
--- a/vespalib/src/vespa/vespalib/util/CMakeLists.txt
+++ b/vespalib/src/vespa/vespalib/util/CMakeLists.txt
@@ -38,6 +38,7 @@ vespa_add_library(vespalib_vespalib_util OBJECT
     memoryusage.cpp
     mmap_file_allocator.cpp
     mmap_file_allocator_factory.cpp
+    monitored_refcount.cpp
     printable.cpp
     priority_queue.cpp
     random.cpp
diff --git a/vespalib/src/vespa/vespalib/util/monitored_refcount.cpp b/vespalib/src/vespa/vespalib/util/monitored_refcount.cpp
new file mode 100644
index 00000000000..4376e26bb66
--- /dev/null
+++ b/vespalib/src/vespa/vespalib/util/monitored_refcount.cpp
@@ -0,0 +1,44 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#include "monitored_refcount.h"
+#include <cassert>
+
+namespace vespalib {
+
+MonitoredRefCount::MonitoredRefCount()
+    : _lock(),
+      _cv(),
+      _refCount(0u)
+{
+}
+
+MonitoredRefCount::~MonitoredRefCount()
+{
+    assert(_refCount == 0u);
+}
+
+void
+MonitoredRefCount::retain() noexcept
+{
+    std::lock_guard<std::mutex> guard(_lock);
+    ++_refCount;
+}
+
+void
+MonitoredRefCount::release() noexcept
+{
+    std::lock_guard<std::mutex> guard(_lock);
+    --_refCount;
+    if (_refCount == 0u) {
+        _cv.notify_all();
+    }
+}
+
+void
+MonitoredRefCount::waitForZeroRefCount()
+{
+    std::unique_lock<std::mutex> guard(_lock);
+    _cv.wait(guard, [this] { return (_refCount == 0u); });
+}
+
+}
diff --git a/vespalib/src/vespa/vespalib/util/monitored_refcount.h b/vespalib/src/vespa/vespalib/util/monitored_refcount.h
new file mode 100644
index 00000000000..465284b6fd3
--- /dev/null
+++ b/vespalib/src/vespa/vespalib/util/monitored_refcount.h
@@ -0,0 +1,29 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+#pragma once
+
+#include <mutex>
+#include <condition_variable>
+
+namespace vespalib {
+
+class RetainGuard;
+/*
+ * Class containing a reference count that can be waited on to become zero.
+ * Typically ancestor or member of a class that has to be careful of when
+ * portions object can be properly torn down before destruction itself.
+ */
+class MonitoredRefCount
+{
+    std::mutex              _lock;
+    std::condition_variable _cv;
+    uint32_t                _refCount;
+    void retain() noexcept;
+    void release() noexcept;
+    friend RetainGuard;
+public:
+    MonitoredRefCount();
+    virtual ~MonitoredRefCount();
+    void waitForZeroRefCount();
+};
+
+}
diff --git a/vespalib/src/vespa/vespalib/util/retain_guard.h b/vespalib/src/vespa/vespalib/util/retain_guard.h
new file mode 100644
index 00000000000..090f3ce75cf
--- /dev/null
+++ b/vespalib/src/vespa/vespalib/util/retain_guard.h
@@ -0,0 +1,45 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#pragma once
+
+#include "monitored_refcount.h"
+
+namespace vespalib {
+
+/*
+ * Class containing a reference to a monitored reference count,
+ * intended to block teardown of the class owning the monitored
+ * reference count.
+ */
+class RetainGuard {
+public:
+    RetainGuard(MonitoredRefCount & refCount) noexcept
+        : _refCount(&refCount)
+    {
+        _refCount->retain();
+    }
+    RetainGuard(const RetainGuard & rhs) = delete;
+    RetainGuard & operator=(const RetainGuard & rhs) = delete;
+    RetainGuard(RetainGuard && rhs) noexcept
+        : _refCount(rhs._refCount)
+    {
+        rhs._refCount = nullptr;
+    }
+    RetainGuard & operator=(RetainGuard && rhs) noexcept {
+        release();
+        _refCount = rhs._refCount;
+        rhs._refCount = nullptr;
+        return *this;
+    }
+    ~RetainGuard() { release(); }
+private:
+    void release() noexcept{
+        if (_refCount != nullptr) {
+            _refCount->release();
+            _refCount = nullptr;
+        }
+    }
+    MonitoredRefCount * _refCount;
+};
+
+}