[IGNITE-13997] CPP Thin: Transactions can cause deadlock when client shared in multiple threads

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.9.1
• Component/s: thin client
• Ignite Flags: Docs Required, Release Notes Required
• Assignee: Unassigned
• Reporter: Igor Sapego
• Created: 14/Jan/21 16:48
• Updated: 14/Jan/21 16:48

Description

In our tests we have detected a deadlock when following piece of code is
executed for more than one thread on our application:

ClientTransactions transactions = client.ClientTransactions();
ClientTransaction tx = transactions.TxStart(PESSIMISTIC, READ_COMMITTED);

// This call should atomically get the current value for "key" and put
"value" instead, locking the "key" cache entry at the same time
auto oldValue = cache.GetAndPut(key, value);

// Only the thread able of locking "key" should reach this code. Others have
to wait for tx.Commit() to complete
cache.Put (key, newValue);

// After this call, other thread waiting in GetAndPut for "key" to be
released should be able of continuing
tx.Commit ();

The thread reaching "cache.Put (key, newValue);" call, gets blocked in
there, concretely in the lockGuard object created at the beginning of
DataChannel::InternalSyncMessage function (data_channel.cpp:108). After
debugging, we realized that this lockGuard is owned by a different thread,
which is currently waiting on socket while executing GetAndPut function.
According to this, my guess is that data routing for C++ Thin Clients is not
multithread friendly.

Reported in http://apache-ignite-users.70518.x6.nabble.com/Multithread-transactions-in-a-C-Thin-Client-td35145.html