CKR_OPERATION_NOT_INITIALIZED in multithreaded application

[BaerMitUmlaut]

I'm working on a multithreaded application and I'm currently having some trouble with a CKR_OPERATION_NOT_INITIALIZED error thrown in the last line of this block:

Pkcs11Interop/src/Pkcs11Interop/HighLevelAPI41/Session.cs

Lines 991 to 998 in 47e4e17

	CKR rv = _pkcs11Library.C_DecryptInit(_sessionId, ref ckMechanism, ConvertUtils.UInt32FromUInt64(keyHandle.ObjectId));
	if (rv != CKR.CKR_OK)
	throw new Pkcs11Exception("C_DecryptInit", rv);
	NativeULong decryptedDataLen = 0;
	rv = _pkcs11Library.C_Decrypt(_sessionId, encryptedData, ConvertUtils.UInt32FromInt32(encryptedData.Length), null, ref decryptedDataLen);
	if (rv != CKR.CKR_OK)
	throw new Pkcs11Exception("C_Decrypt", rv);

Screenshot

As far as I understand, this error is thrown when the encryption or decryption operation is not initialized and from what I've read, an operation stays initialized until data is decrypted. My best guess is that the following is happening:

Thread A	Thread B	Initialized
C_DecryptInit		Yes
	C_DecryptInit	Yes
C_Decrypt		No
	C_Decrypt	⚡

Thus a lock would be required to make the call to Session.Encrypt / Session.Decrypt thread safe.