Multiple C# Threads calling WASM Module

[alc-aardvark]

I have tried to run a WASM module from a C# unit test where there are 2 threads calling the module in a loop. This dies with one of the threads ending in with the following exception

wasm trap: call stack exhausted

Here is logged output from the Test where

• [n] is the thread number
• Count is the iterations for that thread
• Error Count is whether the result was in error (as I was checking for race conditions)
• Exception is the C# exception that was caught from the WASM method Invoke

Debug Trace:
[0]   Count: 0   ErrorCount: 0   Exception: error while executing at wasm backtrace:
    0: <unknown>!<wasm function 37>
    1:  0xb25 - <unknown>!<wasm function 14>
    2: 0x47d8 - <unknown>!<wasm function 37>

Caused by:
    wasm trap: call stack exhausted
[1]   Count: 89498   ErrorCount: 0   Exception: 

It is like the WASM module method is being called OK by one thread while the other thread is looks to be calling the method but never leaving it and the stack eventually blew up??

If I run this as 1 thread OR put a C# Lock {} block around the WASM method call, then it all runs fine, and I have called the method for over 5,000,000 iterations without an issue.

The WASM module was written in C and and generated using Emscripten. The method takes in two string (pointers) and a an Int64 and returns a string (pointer).

The memory is being Free'ed.

C method
char* TryVerify(char* token, char* originHeader, uint64_t serverUtcUnixNowMilliseconds)

C# call

        object lockObject = new object();
        public bool TryVerify(string token, string originHeader, out TokenData tokenData)
        {
            //lock (lockObject)
            //{
                var serverUtcUnixNowMilliseconds = new DateTimeOffset(DateTime.UtcNow).ToUnixTimeMilliseconds();
                int inPtrToken = WriteStringToUTF8(token);
                int inPtrOriginHeader = WriteStringToUTF8(originHeader);
                int outPtr = _TryVerify.Invoke(inPtrToken, inPtrOriginHeader, serverUtcUnixNowMilliseconds);
                var json = Memory.ReadNullTerminatedString(outPtr);
                _Free(outPtr);

                tokenData = System.Text.Json.JsonSerializer.Deserialize<TokenData>(json, new JsonSerializerOptions() { PropertyNameCaseInsensitive = true }) ?? throw new Exception("Failed to deserialize token data from wasm");
                if (tokenData == null)
                {
                    tokenData = new TokenData();
                }

                return tokenData.IsOk;
           // }
        }