The text "operation would block" is perhaps a little misleading. As the error text indicates, this just means the statement in question can't complete right now:

"Cause: This is a status code that indicates that the operation cannot complete now.

Action: None; this is not an error. The operation should be retried again for completion."

http://docs.oracle.com/database/122/ERRMG/ORA-02140.htm#GUID-008ABD32-275E-467A-AE6B-04976F2A8462__GUID-66A2A4B8-66F2-4A13-B73D-74FFE4728C58

There's many reasons this could happen. For example, you may be trying to insert to a table locked in exclusive mode:

https://community.oracle.com/message/373286

As discussed in the OCI Programmer's Guide, you need to test this in your code:

"OCI provides the ability to establish a server connection in blocking mode or nonblocking mode. When a connection is made in blocking mode, an OCI call returns control to an OCI client application only when the call completes, either successfully or in error. With the nonblocking mode, control is immediately returned to the OCI program if the call could not complete, and the call returns a value of OCI_STILL_EXECUTING.

In nonblocking mode, an application must test the return code of each OCI function to see if it returns OCI_STILL_EXECUTING. If it does, the OCI client can continue to process program logic while waiting to retry the OCI call to the server. This mode is particularly useful in graphical user interface (GUI) applications, real-time applications, and in distributed environments."

http://docs.oracle.com/database/122/LNOCI/oci-programming-basics.htm#LNOCI16240