DTWAIN Handles and Threading Issues

Internally, DTWAIN associates the handle returned by DTWAIN_SysInitialize or DTWAIN_SysInitializeEx with the current thread identifier (thread ID). When a subsequent call to a DTWAIN API function is done, DTWAIN checks that the thread identifier originally used in DTWAIN_SysInitialize is still the current thread. If not, a -1001 error (DTWAIN not initialized) is returned.

Therefore under normal circumstances, DTWAIN will not run across threads without some modifications, which are discussed below.

To overcome the -1001 error when using multiple threads, there are two scenarios possible:

1.	Running multiple sessions of DTWAIN, one session for each thread or

2.	Running a single session of DTWAIN in more than one thread.

To allow DTWAIN to be used in a multithreaded application, a call to DTWAIN_UseMultipleThreads(TRUE) must be done to ensure that the DTWAIN library will recognize it will be used in a multithreaded fashion.

In the following sections, references to DTWAIN_SysInitialize also apply to DTWAIN_SysInitializeEx.

Multiple DTWAIN Sessions

Single DTWAIN Session