InvalidMemoryOperationError with MySQL pool under heavy load

[Abscissa]

Not sure if this is an issue with Vibe.d or mysqln (or DMD/druntime for that matter), so I'm posting it here. I don't know whether or not this might have anything to do with the mysql pool not reopening forcibly-closed connections.

My setup: Win7 64-bit 2-core, DMD 2.060 32-bit, Vibe.d v0.7.8, Vibe.d's branch of mysqln

Test source:

import mysql.db;
import vibe.d;

MysqlDB dbPool;
static this()
{
    dbPool = new MysqlDB("localhost", "testdbuser", "testpass", "testdb");

    auto settings = new HttpServerSettings();
    settings.port = 8181;

    auto router = new UrlRouter();
    router.get("/dbtest", &doDB);

    listenHttp(settings, router);
}

void doDB(HttpServerRequest req, HttpServerResponse res)
{
    auto conn = dbPool.lockConnection();
    res.writeBody("hi");
}

If I do:

ab -r -n 1000 -c 1000 http://127.0.0.1:8181/dbtest

Then I randomly get one of the following results:

[00A80F80:00000000 INF] Running event loop...
core.exception.InvalidMemoryOperationError
core.exception.InvalidMemoryOperationError

Or:

[02240F80:00000000 INF] Running event loop...
[02240F80:00000000 ERR] Unhandled exception in event loop: core.exception.Assert
[email protected](262): Assertion failure
----------------
0x004F34EC in char[][] core.sys.windows.stacktrace.StackTrace.trace()
0x004F3377 in core.sys.windows.stacktrace.StackTrace core.sys.windows.stacktrace.StackTrace.__ctor()
0x004D5D17 in onAssertError
0x0046C7DA in extern (C) void vibe.core.drivers.libevent2.Libevent2Driver.onDnsResult(int, char, int, int, void*, void*) at C:\DevProj\darticles\..\vibe.d-0.7.8\source\vibe\core\drivers\libevent2.d(263)
0x6842E05C in evdns_set_log_fn
0x00486287 in int vibe.core.core.runEventLoop() at C:\DevProj\darticles\..\vibe.d-0.7.8\source\vibe\core\core.d(58)
0x0048E4CF in _Dmain at C:\DevProj\darticles\..\vibe.d-0.7.8\source\vibe\appmain.d(38)
0x004CFB98 in extern (C) int rt.dmain2.main(int, char**).void runMain()
0x004CFBD2 in extern (C) int rt.dmain2.main(int, char**).void runAll()
0x004CF7F4 in main
0x004F9FC5 in mainCRTStartup
0x7539339A in BaseThreadInitThunk
0x77A69EF2 in RtlInitializeExceptionChain
0x77A69EC5 in RtlInitializeExceptionChain
core.exception.InvalidMemoryOperationError

[Abscissa]

This seems likely a duplicate of #30. If further investigation reveals they're separate, we can reopen.