Threading in GDB (Debugging with GDB)

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#### 23.3.2.2 Threading in GDB

GDB is not thread-safe. If your Python program uses multiple threads, you must be careful to only call GDB-specific functions in the GDB thread. GDB provides some functions to help with this.

Function: gdb.block_signals ()

  As mentioned earlier (see Basic Python), certain signals must be delivered to the GDB main thread. The `block_signals` function returns a context manager that will block these signals on entry. This can be used when starting a new thread to ensure that the signals are blocked there, like:

      with gdb.block_signals():
         start_new_thread()

class: gdb.Thread

  This is a subclass of Python’s `threading.Thread` class. It overrides the `start` method to call `block_signals`, making this an easy-to-use drop-in replacement for creating threads that will work well in GDB.

Function: gdb.interrupt ()

  This causes GDB to react as if the user had typed a control-C character at the terminal. That is, if the inferior is running, it is interrupted; if a GDB command is executing, it is stopped; and if a Python command is running, `KeyboardInterrupt` will be raised.

  Unlike most Python APIs in GDB, `interrupt` is thread-safe.

Function: gdb.post_event (event)

  Put event, a callable object taking no arguments, into GDB’s internal event queue. This callable will be invoked at some later point, during GDB’s event processing. Events posted using `post_event` will be run in the order in which they were posted; however, there is no way to know when they will be processed relative to other events inside GDB.

  Unlike most Python APIs in GDB, `post_event` is thread-safe. For example:

      (gdb) python
      >import threading
      >
      >class Writer():
      > def __init__(self, message):
      >        self.message = message;
      > def __call__(self):
      >        gdb.write(self.message)
      >
      >class MyThread1 (threading.Thread):
      > def run (self):
      >        gdb.post_event(Writer("Hello "))
      >
      >class MyThread2 (threading.Thread):
      > def run (self):
      >        gdb.post_event(Writer("World\n"))
      >
      >MyThread1().start()
      >MyThread2().start()
      >end
      (gdb) Hello World

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