1 files changed, 67 insertions, 0 deletions
diff --git a/src/mongo/db/stats/fine_clock.h b/src/mongo/db/stats/fine_clock.h
new file mode 100644
index 00000000000..02600e718c4
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+++ b/src/mongo/db/stats/fine_clock.h
@@ -0,0 +1,67 @@
+// fine_clock.h
+
+/**
+*    Copyright (C) 2008 10gen 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/>.
+*/
+
+#ifndef DB_STATS_FINE_CLOCK_HEADER
+#define DB_STATS_FINE_CLOCK_HEADER
+
+#include <time.h>  // struct timespec
+
+namespace mongo {
+
+    /**
+     * This is a nano-second precision clock. We're skipping the
+     * harware TSC in favor of clock_gettime() which in some systems
+     * does not involve a trip to the OS (VDSO).
+     *
+     * We're exporting a type WallTime that is and should remain
+     * opaque. The business of getting accurate time is still ongoing
+     * and we may change the internal representation of this class.
+     * (http://lwn.net/Articles/388188/)
+     *
+     * Really, you shouldn't be using this class in hot code paths for
+     * platforms you're not sure whether the overhead is low.
+     */
+    class FineClock {
+    public:
+
+        typedef timespec WallTime;
+
+        static WallTime now() {
+            struct timespec ts;
+            clock_gettime(CLOCK_MONOTONIC, &ts);
+            return ts;
+        }
+
+        static uint64_t diffInNanos( WallTime end, WallTime start ) {
+            uint64_t diff;
+            if ( end.tv_nsec < start.tv_nsec ) {
+                diff = 1000000000 * ( end.tv_sec - start.tv_sec - 1);
+                diff += 1000000000 + end.tv_nsec - start.tv_nsec;
+            }
+            else {
+                diff = 1000000000 * ( end.tv_sec - start.tv_sec );
+                diff += end.tv_nsec - start.tv_nsec;
+            }
+            return diff;
+        }
+
+    };
+}
+
+#endif  // DB_STATS_FINE_CLOCK_HEADER
+