Use boost::asio::deadline_timer for walletpassphrase timeout

New method in bitcoinrpc:  RunLater, that uses a map of deadline
timers to run a function later.

Behavior of walletpassphrase is changed; before, calling
walletpassphrase again before the lock timeout passed
would result in: Error: Wallet is already unlocked.

You would have to call lockwallet before walletpassphrase.

Now: the last walletpassphrase with correct password
wins, and overrides any previous timeout.

Fixes issue# 1961 which was caused by spawning too many threads.

Test plan:

Start with encrypted wallet, password 'foo'
NOTE:
 python -c 'import time; print("%d"%time.time())'
... will tell you current unix timestamp.

Try:

walletpassphrase foo 600
getinfo
EXPECT: unlocked_until is about 10 minutes in the future

walletpassphrase foo 1
sleep 2
sendtoaddress mun74Bvba3B1PF2YkrF4NsgcJwHXXh12LF 11
EXPECT: Error: Please enter the wallet passphrase with walletpassphrase first.

walletpassphrase foo 600
walletpassphrase foo 0
getinfo
EXPECT: wallet is locked (unlocked_until is 0)

walletpassphrase foo 10
walletpassphrase foo 600
getinfo
EXPECT: wallet is unlocked until 10 minutes in future

walletpassphrase foo 60
walletpassphrase bar 600
EXPECT: Error, incorrect passphrase
getinfo
EXPECT: wallet still scheduled to lock 60 seconds from first (successful) walletpassphrase

src/bitcoinrpc.cpp

@@ -11,17 +11,17 @@
 #include "bitcoinrpc.h"
 #include "db.h"
 
+#include <boost/algorithm/string.hpp>
 #include <boost/asio.hpp>
 #include <boost/asio/ip/v6_only.hpp>
+#include <boost/asio/ssl.hpp>
 #include <boost/bind.hpp>
 #include <boost/filesystem.hpp>
+#include <boost/filesystem/fstream.hpp>
 #include <boost/foreach.hpp>
 #include <boost/iostreams/concepts.hpp>
 #include <boost/iostreams/stream.hpp>
-#include <boost/algorithm/string.hpp>
 #include <boost/lexical_cast.hpp>
-#include <boost/asio/ssl.hpp>
-#include <boost/filesystem/fstream.hpp>
 #include <boost/shared_ptr.hpp>
 #include <list>
 
@@ -34,6 +34,7 @@ static std::string strRPCUserColonPass;
 
 // These are created by StartRPCThreads, destroyed in StopRPCThreads
 static asio::io_service* rpc_io_service = NULL;
+static map<string, boost::shared_ptr<deadline_timer> > deadlineTimers;
 static ssl::context* rpc_ssl_context = NULL;
 static boost::thread_group* rpc_worker_group = NULL;
 
@@ -843,6 +844,7 @@ void StopRPCThreads()
 {
     if (rpc_io_service == NULL) return;
 
+    deadlineTimers.clear();
     rpc_io_service->stop();
     rpc_worker_group->join_all();
     delete rpc_worker_group; rpc_worker_group = NULL;
@@ -850,6 +852,26 @@ void StopRPCThreads()
     delete rpc_io_service; rpc_io_service = NULL;
 }
 
+void RPCRunHandler(const boost::system::error_code& err, boost::function<void(void)> func)
+{
+    if (!err)
+        func();
+}
+
+void RPCRunLater(const std::string& name, boost::function<void(void)> func, int64 nSeconds)
+{
+    assert(rpc_io_service != NULL);
+
+    if (deadlineTimers.count(name) == 0)
+    {
+        deadlineTimers.insert(make_pair(name,
+                                        boost::shared_ptr<deadline_timer>(new deadline_timer(*rpc_io_service))));
+    }
+    deadlineTimers[name]->expires_from_now(posix_time::seconds(nSeconds));
+    deadlineTimers[name]->async_wait(boost::bind(RPCRunHandler, _1, func));
+}
+
+
 class JSONRequest
 {
 public: