When running walletpassphrase on a large wallet.dat (ie about 300,000 segwit P2SH addresses) the command sometimes takes a very long time, and if command is run multiple times at once (while running slow) it causes bitcoin core to freeze (stops syncing and requires kill -9 to stop/restart)

During the locked up walletpassphrase commands being run the following messages start to appear in the debug.log:

`018-01-24 01:01:04 socket sending timeout: 1201s`

Note that this problem is intermittent, so sometimes the command runs instantly, other times it takes a few minutes, and other times it completely freezes the node.
#include <wallet/walletdb.h>
#include <fs.h>
#include <key_io.h>
#include <protocol.h>
#include <serialize.h>
#include <sync.h>
#include <util/system.h>
#include <util/time.h>
#include <wallet/wallet.h>
#include <atomic>
#include <string>
#include <boost/thread.hpp>
namespace DBKeys {
const std::string ACENTRY{"acentry"};
const std::string ACTIVEEXTERNALSPK{"activeexternalspk"};
const std::string ACTIVEINTERNALSPK{"activeinternalspk"};
const std::string BESTBLOCK_NOMERKLE{"bestblock_nomerkle"};
const std::string BESTBLOCK{"bestblock"};
const std::string CRYPTED_KEY{"ckey"};
const std::string CSCRIPT{"cscript"};
const std::string DEFAULTKEY{"defaultkey"};
const std::string DESTDATA{"destdata"};
const std::string FLAGS{"flags"};
const std::string HDCHAIN{"hdchain"};
const std::string KEYMETA{"keymeta"};
const std::string KEY{"key"};
const std::string MASTER_KEY{"mkey"};
const std::string MINVERSION{"minversion"};