I have a bug I am chasing (I think its a deadlock). When I run the code it hangs without the debugger flagging an error, so after a while I try pressing the pause (break all) button. The debugger then reports “The process appears to be deadlocked…”. I then can see that all the threads are held up at lines saying EnterCriticalSection except for one which is already inside a critical section. When I look at the thread that is inside the C.S. with the debugger I see a green arrow, accompanied by a tiny blue circle pointing at a line with GetWindowText… as below:
// stuff A
{
GetWindowText(editwin[a].child_window_handle,existing_text,MAX_TEXT_SIZE-1);
}
// stuff B
If I hover the mouse over the green arrow I see the text “this is the next statement to execute when this thread returns from the current function”. Now this has stumped me because I don’t know if it means that it is stuck inside “stuff A” and is waiting to come back or its stuck inside GetWindowText and has somehow got stuck inside that. The arguments to GetWindowText all look sensible to me. If I click on “step into” I get the message “Unable to step. The process has been soft broken”.
EDIT: stuff A is in fact the statement:
if (buf_ptr != NULL)
Your problem is that GetWindowText actually sends a message to the other window and waits for it to return. If that window is owned by another thread that is waiting for a critical section, GetWindowText will wait forever.
You’re stuck inside GetWindowText, and have created a deadlock.