AppHangXProcB1 on our 32 bit application - c

Question

We have a C program (a client that connects to our server). The program uses Win32 API:s to create controls etc. It is a single-threaded application. Lately the application has started to hang at random in Windows 7.
Thanks to Application Verifier, I could detect problematic APIs and rectified them.
Now there are still some customers reporting a "non-responsive" situation.
A crash dump from their side reveals the following API:
SendMessage(HWND_BROADCAST, WM_DDE_INITIATE, (WPARAM)hClient, MAKELONG(aAppl,aTopic));
Yes its sending a DDE command to WinWord.exe. Task Manager shows Winword in non-responsive state.
Evtx reveals the following:
Fault bucket , type 0
Event Name: AppHangXProcB1
Response: Not available
Cab Id: 0
Problem signature:
P1: OurApplication.exe
P2: 14.14.1.50
P3: 537337f4
P4: b6f1
P5: 32
P6: WINWORD.EXE
P7: 15.0.4615.1000
P8:
P9:
P10:
Attached files:
C:\Users\diane-do\AppData\Local\Temp\WER91C7.tmp.appcompat.txt
C:\Users\diane-do\AppData\Local\Temp\WER958F.tmp.WERInternalMetadata.xml
C:\Users\diane-do\AppData\Local\Temp\WER968B.tmp.xml
C:\Users\diane-do\AppData\Local\Temp\WER969C.tmp.hdmp
C:\Users\diane-do\AppData\Local\Temp\WER9777.tmp.mdmp
These files may be available here:
C:\Users\diane-do\AppData\Local\Microsoft\Windows\WER\ReportQueue\AppHang_OurApplication.exe_e9b582fc22d416b8787c1184f6fe7fa19d63_cab_0fde97a1
Analysis symbol:
Rechecking for solution: 0
Report Id: 9e84daa9-eff8-11e3-a2fb-90b11c841d1a
Report Status: 36
Any help would be appreciated.
Please note the above is Win 7 64-bit, while our application is 32 bit. Don't know what build their Office 2013 is (32 or 64 bit)
I am aware of the following:
- DDE is old technology, but changing it is out of question now.
- For the above case, I cant use SendMessageTimeout APIs as our client has to wait until commands complete.
ONCE AGAIN, The hang (non-responsive state) happens at random, not always at DDE but various instances. While computing something, even while doing a simple operation as below. Customers launch our CHM file from our menu, then Alt+Tab to another application and then Alt+Tab back to our application, our application becomes non-responsive.
P.S: I also didn't find any document online as to how to interpret those evtx application logs , what P1 P2 stand for. What signatures meant or what fault bucket type are, or any meaning of AppHangXProcB1 or AppHangB1 etc. Please pass the link if you have for the same.

Answer 1

sendmessage is a blocking call it will return only after the receiver application processes the message. Here, it got blocked & it as well blocked your application from dispatching the message. Since your application can't process any further window messages, it hanged the GUI.
Check again all the processing done on processing a window message for any blocking calls like waitforsingleobject, recv, connect in it.