Multiple DTWAIN Sessions
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You are allowed to make multiple calls to DTWAIN_SysInitialize in different threads. Each call to DTWAIN_SysInitialize will return a unique handle, Therefore your application can run a DTWAIN session in one thread, and another complete DTWAIN session in another thread.
However, a thread that calls DTWAIN_SysInitialize cannot "communicate" with another thread that called DTWAIN_SysInitialize. For example, if you call DTWAIN_SysInitialize in thread 1, and DTWAIN_SysInitialize in thread 2, you cannot select a TWAIN Source in thread 1 using DTWAIN_SelectSource( ) and use it for a DTWAIN API function in thread 2.
For example:
//Thread 1 (main thread): DTWAIN_SysInitialize( ); DTWAIN_SOURCE Source = DTWAIN_SelectSource( ); //.... // Start of thread 2 (assume values from thread 1 have been passed to thread 2) DTWAIN_CloseSource( Source ); // -1001 error since the Source was selected in thread 1, and we are using it in thread 2 //.... // ....
Note that an error is returned, since Source was selected and opened in thread 1, and was attempted to be used in the DTWAIN_CloseSource function in thread 2. The following scenario is valid:
//Thread 1 (main thread): DTWAIN_UseMultipleThreads(TRUE); // Must be called to ensure proper thread handling DTWAIN_SysInitialize( ); DTWAIN_SOURCE Source = DTWAIN_SelectSource( ); //.... // Start of thread 2 (assume values from thread 1 have been passed to thread 2) DTWAIN_SysInitialize( ); // call again for new thread DTWAIN_SOURCE Source2 = DTWAIN_SelectSource( ); DTWAIN_CloseSource( Source2 ); // OK //.... // .... // End of thread 2
This scenario calls DTWAIN_SysInitialize( ) for each thread.
Before exiting the thread when using multiple sessions of DTWAIN, you must call DTWAIN_SysDestroy. If not, there will be memory leaks in your application.
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