Signal Exceptions

Signal exceptions are special events sent to a thread when the user presses certain key sequences or when another thread or process explicitly initiates the exception. There are three types of signal exceptions:

XCPT_SIGNAL_BREAK

When the user presses Ctrl+Break

When the user presses Ctrl+C

DosKillProcess

Signal exceptions are sent only to Thread 1 (the main thread) in the process receiving the exception. If an exception handler is registered on Thread 1, it must be prepared to receive signal exceptions. The thread 1 exception handler can always ignore the signal exception by returning XCPT_CONTINUE_SEARCH.

If the thread 1 exception handler is to receive signal exceptions, it must use DosSetSignalExceptionFocus to notify OS/2 that it wants to receive the XCPT_SIGNAL_INTR (Ctrl+C) and XCPT_SIGNAL_BREAK (Ctrl+Break) signals. Otherwise, these exceptions are not passed to the exception handler and the default action-to terminate the process-is taken by OS/2. The thread will get XCPT_SIGNAL_KILLPROC signals whether it uses DosSetSignalExceptionFocus or not.

All three of these signals are delivered by a single exception-XCPT_SIGNAL-and the exception handler for Thread 1 can choose to handle none, some, or all of the signals. The signal being sent can be determined by examining the exception information in EXCEPTIONREPORTRECORD.

The following table provides information about each type of signal.

Signal Exceptions

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ГCtrl+Break  ГXCPT_SIGNAL_BREAK         ГThis exception is sent to  Г
Г            Г                          ГThread 1 in the current    Г
Г            Г                          Гkeyboard-focus process whenГ
Г            Г                          Гa Ctrl+Break key sequence  Г
Г            Г                          Гis received from the       Г
Г            Г                          Гkeyboard. The default      Г
Г            Г                          Гaction taken by OS/2 for   Г
Г            Г                          Гthis exception is forced   Г
Г            Г                          Гprocess termination.       Г
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ГCtrl+C      ГXCPT_SIGNAL_INTR          ГThis exception is sent to  Г
Г            Г                          ГThread 1 in the current    Г
Г            Г                          Гkeyboard-focus process whenГ
Г            Г                          Гa Ctrl+C key sequence is   Г
Г            Г                          Гreceived from the keyboard.Г
Г            Г                          ГThe default action taken byГ
Г            Г                          ГOS/2 for this exception is Г
Г            Г                          Гforced process termination.Г
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ГKill ProcessГXCPT_SIGNAL_KILLPROC      ГThis exception is sent to  Г
ГSignal      Г                          ГThread 1 in the process    Г
Г            Г                          Гspecified when an          Г
Г            Г                          Гapplication uses           Г
Г            Г                          ГDosKillProcess. The        Г
Г            Г                          ГXCPT_SIGNAL_KILLPROC signalГ
Г            Г                          Гexception results from an  Г
Г            Г                          Гaction external to the     Г
Г            Г                          Гprocess. The default actionГ
Г            Г                          Гtaken by OS/2 for this     Г
Г            Г                          Гexception is forced processГ
Г            Г                          Гtermination.               Г
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