When i used the encrypted wallet to test transfer parallelly,i frequently got the trouble: The rpc server is not responding.My test script is like below:
#!/bin/sh
while [ 1 ]
do
./bitcoin-cli listaddressgroupings>null
./bitcoin-cli walletpassphrase "!@#$%^&*" 2
./bitcoin sendtoaddress "mhAW6mzs5DeCbzBUHXBi4U446Fdnr1z8U7" 0.01
done

When i open the dead lock trace macro and check the debug log,i found the last print is as below:
2018-12-17 08:27:58 ThreadRPCServer method=walletpassphrase
2018-12-17 08:27:58 LOCKCONTENTION: cs_main
2018-12-17 08:27:58 Locker: wallet/rpcwallet.cpp:2642
2018-12-17 08:27:58 LOCKCONTENTION: pWallet->cs_wallet
2018-12-17 08:27:58 Locker: wallet/rpcwallet.cpp:2607

The line no 2642 is walletpassphrase and 2607 is LockWallet. I checked the code,i found there is no log printed for this line in function "walletpassphrase":
"LogPrint(BCLog::RPC, "queue run of timer %s in %i seconds (using %s)\n", name, nSeconds, timerInterface->Name());" So i guess the reason may be:
When "walletpassphrase" is running and lock the cs_wallet,the last relock timer triggered and call "LockWallet"."LockWallet" want to lock the cs_wallet but it has been locked by "walletpassphrase",so "LockWallet" is blocked.When "walletpassphrase" run to call "RPCRunLater",the function will erase the timer from the std::map "deadlineTimers",but the timer's timeout call is blocked,so the dead lock take place.
Is my guess right?
How to reslove the issue?
Any help will be appreciative！
if (!request.params[2].isNull() && request.params[2].get_bool()) {
        flags |= WALLET_FLAG_BLANK_WALLET;
    }
    SecureString passphrase;
    passphrase.reserve(100);
    std::vector<std::string> warnings;
    if (!request.params[3].isNull()) {
        passphrase = request.params[3].get_str().c_str();
        if (passphrase.empty()) {
            
            warnings.emplace_back("Empty string given as passphrase, wallet will not be encrypted.");
        }
    }
    if (!request.params[4].isNull() && request.params[4].get_bool()) {
        flags |= WALLET_FLAG_AVOID_REUSE;
    }
    std::string error;
    std::shared_ptr<CWallet> wallet;
    WalletCreationStatus status = CreateWallet(*g_rpc_chain, passphrase, flags, request.params[0].get_str(), error, warnings, wallet);
    switch (status) {
        case WalletCreationStatus::CREATION_FAILED:
            throw JSONRPCError(RPC_WALLET_ERROR, error);
        case WalletCreationStatus::ENCRYPTION_FAILED:
            throw JSONRPCError(RPC_WALLET_ENCRYPTION_FAILED, error);
        case WalletCreationStatus::SUCCESS:
            break;
        
    }
    UniValue obj(UniValue::VOBJ);
    obj.pushKV("name", wallet->GetName());