diff --git a/contrib/fb303/TClientInfo.h b/contrib/fb303/TClientInfo.h
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#ifndef _FACEBOOK_THRIFT_SERVER_TCLIENTINFO_H_
+#define _FACEBOOK_THRIFT_SERVER_TCLIENTINFO_H_ 1
+
+// for inet_ntop --
+#include <arpa/inet.h>
+#include <server/TServer.h>
+#include <transport/TSocket.h>
+#include <concurrency/Mutex.h>
+
+namespace apache { namespace thrift { namespace server {
+
+using namespace apache::thrift;
+using namespace apache::thrift::transport;
+using namespace apache::thrift::concurrency;
+using boost::shared_ptr;
+using std::string;
+using std::vector;
+
+/**
+ * StableVector -- a minimal vector class where growth is automatic and
+ * vector elements never move as the vector grows.  Allocates new space
+ * as needed, but does not copy old values.
+ *
+ * A level vector stores a list of storage vectors containing the actual
+ * elements.  Levels are added as needed, doubling in size each time.
+ * Locking is only done when a level is added.  Access is amortized
+ * constant time.
+ */
+template <typename T>
+class StableVector {
+  /// The initial allocation as an exponent of 2
+  static const uint32_t kInitialSizePowOf2 = 10;
+  /// The initial allocation size
+  static const uint32_t kInitialVectorSize = 1 << kInitialSizePowOf2;
+  /// This bound is guaranteed not to be exceeded on 64-bit archs
+  static const int kMaxLevels = 64;
+
+  /// Values are kept in one or more of these
+  typedef vector<T> Vect;
+  /// One or more value vectors are kept in one of these
+  typedef vector<Vect*> LevelVector;
+
+  Mutex mutex_;
+  /// current size
+  size_t size_;
+  _Atomic_word vectLvl_;
+  LevelVector vects_;
+
+ public:
+  /**
+   * Constructor -- initialize the level vector and allocate the
+   * initial storage vector
+   */
+  StableVector()
+    : size_(0) 
+    , vectLvl_(0) {
+    vects_.reserve(kMaxLevels);
+    Vect* storageVector(new Vect(1 << kInitialSizePowOf2));
+    vects_.push_back(storageVector);
+  }
+
+ private:
+  /**
+   * make sure the requested number of storage levels have been allocated.
+   */
+  void expand(uint32_t level) {
+    // we need the guard to insure that we only allocate once.
+    Guard g(mutex_);
+    while (level > vectLvl_) {
+      Vect* levelVect(new Vect(1 << (vectLvl_ + kInitialSizePowOf2)));
+      vects_.push_back(levelVect);
+      // we need to make sure this is done after levelVect is inserted
+      // (what we want is effectively a memory barrier here).
+      __gnu_cxx::__atomic_add(&vectLvl_, 1);
+    }
+  }
+
+  /**
+   * Given an index, determine which level and element of that level is
+   * required.  Grows if needed.
+   */
+  void which(uint32_t n, uint32_t* vno, uint32_t* idx) {
+    if (n >= size_) {
+      size_ = n + 1;
+    }
+    if (n < kInitialVectorSize) {
+      *idx = n;
+      *vno = 0;
+    } else {
+      uint32_t upper = n >> kInitialSizePowOf2;
+      *vno = CHAR_BIT*sizeof(upper) - __builtin_clz(upper);
+      *idx = n - (1 << (*vno + kInitialSizePowOf2 - 1));
+      if (*vno > vectLvl_) {
+        expand(*vno);
+      }
+    }
+  }
+
+ public:
+  /**
+   * Given an index, return a reference to that element, perhaps after
+   * allocating additional space.
+   *
+   * @param n a positive integer
+   */
+  T& operator[](uint32_t n) {
+    uint32_t vno;
+    uint32_t idx;
+    which(n, &vno, &idx);
+    return (*vects_[vno])[idx];
+  }
+
+  /**
+   * Return the present size of the vector.
+   */
+  size_t size() const { return size_; }
+};
+
+
+/**
+ * This class embodies the representation of a single connection during
+ * processing.  We'll keep one of these per file descriptor in TClientInfo.
+ */
+class TClientInfoConnection {
+ public:
+  const static int kNameLen = 32;
+
+ private:
+  typedef union IPAddrUnion {
+    sockaddr_in ipv4;
+    sockaddr_in6 ipv6;
+  };
+
+  char call_[kNameLen];            ///< The name of the thrift call
+  IPAddrUnion addr_;               ///< The client's IP address
+  timespec time_;                  ///< Time processing started
+  uint64_t ncalls_;                ///< # of calls processed
+
+ public:
+  /**
+   * Constructor; insure that no client address or thrift call name is
+   * represented.
+   */
+  TClientInfoConnection();
+
+  /**
+   * A connection has been made; record its address.  Since this is the
+   * first we'll know of a connection we start the timer here as well.
+   */
+  void recordAddr(const sockaddr* addr);
+
+  /**
+   * Mark the address as empty/unknown.
+   */
+  void eraseAddr();
+
+  /**
+   * Return a string representing the present address, or NULL if none.
+   * Copies the string into the buffer provided.
+   */
+  const char* getAddr(char* buf, int len) const;
+
+  /**
+   * A call has been made on this connection; record its name.  Since this is
+   * called for every thrift call processed, we also do our call count here.
+   */ 
+  void recordCall(const char* name);
+
+  /**
+   * Invoked when processing has ended to clear the call name.
+   */
+  void eraseCall();
+
+  /**
+   * Return as string the thrift call either currently being processed or
+   * most recently processed if the connection is still open for additonal
+   * calls.  Returns NULL if a call hasn't been made yet or processing
+   * has ended.
+   */
+  const char* getCall() const;
+
+  /**
+   * Get the timespec for the start of this connection (specifically, when
+   * recordAddr() was first called).
+   */
+  void getTime(timespec* time) const;
+
+  /**
+   * Return the number of calls made on this connection.
+   */
+  uint64_t getNCalls() const;
+
+ private:
+  void initTime();
+};
+
+
+/**
+ * Store for info about a server's clients -- specifically, the client's IP
+ * address and the call it is executing.  This information is indexed by
+ * socket file descriptor and in the present implementation is updated
+ * asynchronously, so it may only approximate reality.
+ */
+class TClientInfo {
+ private:
+  StableVector<TClientInfoConnection> info_;
+
+ public:
+  /**
+   * Return the info object for a given file descriptor.  If "grow" is true
+   * extend the info vector if required (such as for a file descriptor not seen
+   * before).  If "grow" is false and the info vector isn't large enough,
+   * or if "fd" is negative, return NULL.
+   */
+  TClientInfoConnection* getConnection(int fd, bool grow);
+
+  size_t size() const;
+};
+
+/**
+ * This derivation of TServerEventHandler encapsulates the main status vector
+ * and provides context to the server's processing loop via overrides.
+ * Together with TClientInfoCallHandler (derived from TProcessorEventHandler) 
+ * it integrates client info collection into the server.
+ */
+class TClientInfoServerHandler : public TServerEventHandler {
+ private:
+  TClientInfo clientInfo_;
+
+ public:
+  /**
+   * One of these is constructed for each open connection/descriptor and links
+   * to both the status vector (clientInfo_) and that descriptor's entry
+   * within it.
+   */
+  struct Connect {
+    TClientInfo* clientInfo_;
+    TClientInfoConnection* callInfo_;
+
+    explicit Connect(TClientInfo* clientInfo)
+      : clientInfo_(clientInfo)
+      , callInfo_(NULL) {
+    }
+  };
+
+  /**
+   * Generate processor context; we don't know what descriptor we belong to
+   * yet -- we'll get hooked up in contextProcess(). 
+   */
+  void* createContext(boost::shared_ptr<TProtocol> input,
+                      boost::shared_ptr<TProtocol> output);
+
+  /**
+   * Mark our slot as unused and delete the context created in createContext().
+   */
+  void deleteContext(void* processorContext,
+                     boost::shared_ptr<TProtocol> input,
+                     boost::shared_ptr<TProtocol> output);
+  
+  /**
+   * Called in the processing loop just before the server invokes the
+   * processor itself, on the first call we establish which descriptor
+   * we correspond to and set it to that socket's peer IP address.  This
+   * also has the side effect of initializing call counting and connection
+   * timing.  We won't know which call we're handling until the handler
+   * first gets called in TClientInfoCallHandler::getContext().
+   */
+  void processContext(void* processorContext,
+                      shared_ptr<TTransport> transport);
+
+  /**
+   * Get status report for server in the form of a vector of strings.
+   * Each active client appears as one string in the format:
+   *
+   *     FD IPADDR CALLNAME DURATION NCALLS
+   *
+   * where "FD" is the file descriptor for the client's socket, "IPADDR"
+   * is the IP address (as reported by accept()), "CALLNAME" is the
+   * current or most recent Thrift function name, "DURATION" is the
+   * duration of the connection, while NCALLS is the number of Thrift
+   * calls made since the connection was made.  A single space separates
+   * fields.
+   */
+  void getStatsStrings(vector<string>& result);
+};
+
+/**
+ * This class derives from TProcessorEventHandler to gain access to the
+ * function name for the current Thrift call.  We need two versions of
+ * this -- TClientInfoCallStatsHandler is the other -- since in the latter
+ * case we pass through to TFunctionStatHandler to perform Thrift call
+ * stats.
+ */
+class TClientInfoCallHandler : public TProcessorEventHandler {
+ public:
+  virtual void* getContext(const char* fn_name, void* serverContext);
+};
+
+} } } // namespace apache::thrift::server
+
+#endif // !_FACEBOOK_THRIFT_SERVER_TCLIENTINFO_H_