diff --git a/src/rewrite/Context.cpp b/src/rewrite/Context.cpp
index 8c16ccfe4..35c64a68c 100644
--- a/src/rewrite/Context.cpp
+++ b/src/rewrite/Context.cpp
@@ -103,8 +103,7 @@ void Context::initialize (int argc, char** argv)
     tdb.location (expandPath (*path));
 
   // Allow user override of file locking.  Solaris/NFS machines may want this.
-  if (! config.get ("locking", true))
-    tdb.noLock ();
+  tdb.lock (config.get ("locking", true));
 
   // TODO Load pending.data.
   // TODO Load completed.data.
@@ -114,11 +113,12 @@ void Context::initialize (int argc, char** argv)
 ////////////////////////////////////////////////////////////////////////////////
 int Context::run ()
 {
-  throw std::string ("unimplemented Context::run");
   // TODO Dispatch to command handlers.
   // TODO Auto shadow update.
   // TODO Auto gc.
+  // TODO tdb.load (Filter);
 
+  throw std::string ("unimplemented Context::run");
   return 0;
 }
 
diff --git a/src/rewrite/TDB.cpp b/src/rewrite/TDB.cpp
index 3f2d658be..6a4ccb018 100644
--- a/src/rewrite/TDB.cpp
+++ b/src/rewrite/TDB.cpp
@@ -26,14 +26,45 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 #include <string>
+#include <sys/file.h>
 #include "text.h"
 #include "util.h"
 #include "TDB.h"
 #include "task.h"
 
 ////////////////////////////////////////////////////////////////////////////////
+//  The ctor/dtor do nothing.
+//  The lock/unlock methods hold the file open.
+//  There should be only one commit.
+//
+//  +- TDB::TDB
+//  |
+//  |  +- TDB::lock
+//  |  |    open
+//  |  |    [lock]
+//  |  |
+//  |  |  +- TDB::load (Filter)
+//  |  |  |    read all
+//  |  |  |    apply filter
+//  |  |  |    return subset
+//  |  |  |
+//  |  |  +- TDB::add (T)
+//  |  |  |
+//  |  |  +- TDB::update (T, T')
+//  |  |  |
+//  |  |  +- TDB::commit
+//  |  |      write all
+//  |  |
+//  |  +- TDB::unlock
+//  |       [unlock]
+//  |       close
+//  |
+//  +- TDB::~TDB
+//       [TDB::unlock]
+//
 TDB::TDB ()
 : mLock (true)
+, mAllOpenAndLocked (false)
 {
 }
 
@@ -41,7 +72,13 @@ TDB::TDB ()
 TDB::TDB (const TDB& other)
 {
   throw std::string ("unimplemented TDB::TDB");
-  mLocations = other.mLocations;
+  mLocations        = other.mLocations;
+  mLock             = other.mLock;
+  mAllOpenAndLocked = false;  // Deliberately so.
+
+  // Set all to NULL.
+  foreach (location, mLocations)
+    mLocations[location->first] = NULL;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -50,7 +87,13 @@ TDB& TDB::operator= (const TDB& other)
   throw std::string ("unimplemented TDB::operator=");
   if (this != &other)
   {
-    mLocations = other.mLocations;
+    mLocations        = other.mLocations;
+    mLock             = other.mLock;
+    mAllOpenAndLocked = false;  // Deliberately so.
+
+    // Set all to NULL.
+    foreach (location, mLocations)
+      mLocations[location->first] = NULL;
   }
 
   return *this;
@@ -59,6 +102,8 @@ TDB& TDB::operator= (const TDB& other)
 ////////////////////////////////////////////////////////////////////////////////
 TDB::~TDB ()
 {
+  if (mAllOpenAndLocked)
+    unlock ();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -69,7 +114,33 @@ void TDB::location (const std::string& path)
           path +
           "' does not exist, or is not readable and writable.";
 
-  mLocations.push_back (path);
+  mLocations[path] = NULL;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+void TDB::lock (bool lockFile /* = true */)
+{
+  mLock = lockFile;
+
+  foreach (location, mLocations)
+    mLocations[location->first] = openAndLock (location->first);
+
+  mAllOpenAndLocked = true;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+void TDB::unlock ()
+{
+  foreach (location, mLocations)
+  {
+    if (mLocations[location->first] != NULL)
+    {
+      fclose (mLocations[location->first]);
+      mLocations[location->first] = NULL;
+    }
+  }
+
+  mAllOpenAndLocked = false;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -80,6 +151,13 @@ int TDB::load (std::vector <T>& tasks, Filter& filter)
   return 0;
 }
 
+////////////////////////////////////////////////////////////////////////////////
+// TODO Write to transaction log.
+void TDB::add (T& after)
+{
+  throw std::string ("unimplemented TDB::add");
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // TODO Write to transaction log.
 void TDB::update (T& before, T& after)
@@ -101,19 +179,13 @@ void TDB::upgrade ()
   throw std::string ("unimplemented TDB::upgrade");
 }
 
-////////////////////////////////////////////////////////////////////////////////
-void TDB::noLock ()
-{
-  mLock = false;
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 void TDB::getPendingFiles (std::vector <std::string> files)
 {
   files.clear ();
 
   foreach (location, mLocations)
-    files.push_back (*location + "/pending.data");
+    files.push_back (location->first + "/pending.data");
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -122,7 +194,32 @@ void TDB::getCompletedFiles (std::vector <std::string> files)
   files.clear ();
 
   foreach (location, mLocations)
-    files.push_back (*location + "/completed.data");
+    files.push_back (location->first + "/completed.data");
+}
+
+////////////////////////////////////////////////////////////////////////////////
+FILE* TDB::openAndLock (const std::string& file)
+{
+  // Check for access.
+  if (access (file.c_str (), F_OK | R_OK | W_OK))
+    throw std::string ("Task does not have the correct permissions for '") +
+          file + "'.";
+
+  // Open the file.
+  FILE* in = fopen (file.c_str (), "rw");
+  if (!in)
+    throw std::string ("Could not open '") + file + "'.";
+
+  // Lock if desired.  Try three times before failing.
+  int retry = 0;
+  if (mLock)
+    while (flock (fileno (in), LOCK_EX) && ++retry <= 3)
+      delay (0.1);
+
+  if (!in)
+    throw std::string ("Could not lock '") + file + "'.";
+
+  return in;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
diff --git a/src/rewrite/TDB.h b/src/rewrite/TDB.h
index 0e6721fb1..c2f94f697 100644
--- a/src/rewrite/TDB.h
+++ b/src/rewrite/TDB.h
@@ -27,6 +27,7 @@
 #ifndef INCLUDED_TDB
 #define INCLUDED_TDB
 
+#include <map>
 #include <vector>
 #include <string>
 #include "Filter.h"
@@ -40,21 +41,26 @@ public:
   TDB& operator= (const TDB&); // Assignment operator
   ~TDB ();                     // Destructor
 
-  void location (const std::string&);
-  int load (std::vector <T>&, Filter&);
-  void update (T&, T&);
-  int commit ();
-  void upgrade ();
+  void  location (const std::string&);
 
-  void noLock ();
+  void  lock (bool lockFile = true);
+  void  unlock ();
+
+  int   load (std::vector <T>&, Filter&);
+  void  add (T&);
+  void  update (T&, T&);
+  int   commit ();
+  void  upgrade ();
 
 private:
-  void getPendingFiles (std::vector <std::string>);
-  void getCompletedFiles (std::vector <std::string>);
+  void  getPendingFiles (std::vector <std::string>);
+  void  getCompletedFiles (std::vector <std::string>);
+  FILE* openAndLock (const std::string&);
 
 private:
-  std::vector <std::string> mLocations;
+  std::map <std::string, FILE*> mLocations;
   bool mLock;
+  bool mAllOpenAndLocked;
 
   // TODO Need cache of raw file contents.
 };