在多线程环境中从C＃调用Delphi DLL时发生访问冲突

I am calling a DLL function written in Delphi XE2 from C# using P/Invoke. It appears to be working when calls are made sequentially from a single thread. However, when multiple threads are calling the function, the C# host application throws I am calling a DLL function written in Delphi X