Implement method to retrieve current holder of a lease

Along with some more information: last renewal time, and deadline.

src/CMakeLists.txt

@@ -68,6 +68,7 @@ add_library(XrdQuarkDB SHARED
                                       storage/KeyDescriptor.hh
   storage/KeyDescriptorBuilder.cc     storage/KeyDescriptorBuilder.hh
                                       storage/KeyLocators.hh
+                                      storage/LeaseInfo.hh
                                       storage/PatternMatching.hh
                                       storage/ReverseLocator.hh
                                       storage/StagingArea.hh

src/StateMachine.cc

@@ -1058,6 +1058,30 @@ void StateMachine::advanceClock(StagingArea &stagingArea, ClockValue newValue) {
   stagingArea.put(KeyConstants::kStateMachine_Clock, unsignedIntToBinaryString(newValue));
 }
 
+rocksdb::Status StateMachine::lease_get(StagingArea &stagingArea, const std::string &key, ClockValue clockUpdate, LeaseInfo &info) {
+
+  // Advance clock, and clear out any expired leases.
+  maybeAdvanceClock(stagingArea, clockUpdate);
+
+  KeyDescriptor keyinfo = getKeyDescriptor(stagingArea, key);
+
+  if(keyinfo.empty()) {
+    return rocksdb::Status::NotFound();
+  }
+
+  if(keyinfo.getKeyType() != KeyType::kLease) {
+    return wrong_type();
+  }
+
+  LeaseLocator locator(key);
+
+  std::string value;
+  THROW_ON_ERROR(stagingArea.get(locator.toSlice(), value));
+
+  info = LeaseInfo(value, keyinfo.getStartIndex(), keyinfo.getEndIndex());
+  return rocksdb::Status::OK();
+}
+
 void StateMachine::advanceClock(ClockValue newValue, LogIndex index) {
   StagingArea stagingArea(*this);
   advanceClock(stagingArea, newValue);
@@ -1678,6 +1702,10 @@ rocksdb::Status StateMachine::lease_acquire(const std::string &key, const std::s
   CHAIN(index, lease_acquire, key, value, clockUpdate, duration, acquired);
 }
 
+rocksdb::Status StateMachine::lease_get(const std::string &key, ClockValue clockUpdate, LeaseInfo &info, LogIndex index) {
+  CHAIN(index, lease_get, key, clockUpdate, info);
+}
+
 rocksdb::Status StateMachine::lease_release(const std::string &key, LogIndex index) {
   CHAIN(index, lease_release, key);
 }

src/StateMachine.hh

@@ -31,6 +31,7 @@
 #include "storage/KeyLocators.hh"
 #include "storage/ConsistencyScanner.hh"
 #include "storage/KeyConstants.hh"
+#include "storage/LeaseInfo.hh"
 #include <rocksdb/db.h>
 #include <rocksdb/utilities/write_batch_with_index.h>
 #include <rocksdb/utilities/debug.h>
@@ -81,6 +82,7 @@ public:
   void advanceClock(StagingArea &stagingArea, ClockValue newValue);
   rocksdb::Status lease_acquire(StagingArea &stagingArea, const std::string &key, const std::string &value, ClockValue clockUpdate, uint64_t duration, bool &acquired);
   rocksdb::Status lease_release(StagingArea &stagingArea, const std::string &key);
+  rocksdb::Status lease_get(StagingArea &stagingArea, const std::string &key, ClockValue clockUpdate, LeaseInfo &info);
 
   //----------------------------------------------------------------------------
   // API for transactional reads. Can be part of a mixed read-write transaction.
@@ -148,6 +150,7 @@ public:
   rocksdb::Status rawGetAllVersions(const std::string &key, std::vector<rocksdb::KeyVersion> &versions);
   rocksdb::Status lease_acquire(const std::string &key, const std::string &value, ClockValue clockUpdate, uint64_t duration, bool &acquired, LogIndex index = 0);
   rocksdb::Status lease_release(const std::string &key, LogIndex index = 0);
+  rocksdb::Status lease_get(const std::string &key, ClockValue clockUpdate, LeaseInfo &info, LogIndex index = 0);
 
   //----------------------------------------------------------------------------
   // Internal configuration, not exposed to users through 'KEYS' and friends.

src/storage/LeaseInfo.hh

+// ----------------------------------------------------------------------
+// File: LeaseInfo.hh
+// Author: Georgios Bitzes - CERN
+// ----------------------------------------------------------------------
+
+/************************************************************************
+ * quarkdb - a redis-like highly available key-value store              *
+ * Copyright (C) 2018 CERN/Switzerland                                  *
+ *                                                                      *
+ * This program is free software: you can redistribute it and/or modify *
+ * it under the terms of the GNU General Public License as published by *
+ * the Free Software Foundation, either version 3 of the License, or    *
+ * (at your option) any later version.                                  *
+ *                                                                      *
+ * 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 General Public License for more details.                         *
+ *                                                                      *
+ * You should have received a copy of the GNU General Public License    *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.*
+ ************************************************************************/
+
+#ifndef QUARKDB_LEASE_INFO_H
+#define QUARKDB_LEASE_INFO_H
+
+#include <string_view>
+
+namespace quarkdb {
+
+using ClockValue = uint64_t;
+
+class LeaseInfo {
+public:
+  LeaseInfo() {}
+
+  LeaseInfo(const std::string& val, ClockValue ren, ClockValue dl) :
+    value(val), lastRenewal(ren), deadline(dl) {}
+
+  ClockValue getLastRenewal() const {
+    return lastRenewal;
+  }
+
+  ClockValue getDeadline() const {
+    return deadline;
+  }
+
+  std::string_view getValue() const {
+    return value;
+  }
+
+private:
+  std::string value;
+  ClockValue lastRenewal;
+  ClockValue deadline;
+};
+
+}
+#endif

test/state-machine.cc

@@ -835,6 +835,14 @@ TEST_F(State_Machine, Leases) {
     iterator.next();
     ASSERT_FALSE(iterator.valid());
   }
+
+  LeaseInfo info;
+  ASSERT_OK(stateMachine()->lease_get("my-lease-4", ClockValue(25), info));
+  ASSERT_EQ(info.getLastRenewal(), ClockValue(25));
+  ASSERT_EQ(info.getDeadline(), ClockValue(35));
+  ASSERT_EQ(info.getValue(), "some-other-string");
+
+  ASSERT_NOTFOUND(stateMachine()->lease_get("does-not-exist", ClockValue(25), info));
 }
 
 static std::string sliceToString(const rocksdb::Slice &slice) {