cvlib: Update doWithTimeout to block recursive calling

Stop doWithTimeout from being able to be recursively called.
Also reset alarm handler to previous default on timeout func
completion

Change-Id: I43dec86ef8ccaeca401e3a8cd051266ba3e871a2

cloudvision/cvlib/context.py

@@ -82,6 +82,15 @@ class LoggingLevel(IntEnum):
     Critical = 5
 
 
+def monitorTimerHandler(signum, frame):
+    '''
+    A handler function for the timer that will raise our custom exception
+    Needs to be declared out here so that we can compare it to ensure that
+    no ongoing timer is running
+    '''
+    raise TimeoutExpiry
+
+
 class Context:
     '''
     Context object that stores a number of system and user-defined parameters:
@@ -360,11 +369,17 @@ def doWithTimeout(f, timeout: int):
         Takes a function and a timeout in seconds.
         Will call and return the result of f, but raises a cvlib.TimeoutExpiry
         exception if it runs longer than <timeout>
+        NOTE: If there is an attempt to recursively call this function, an InvalidContextException
+        will be raised.
         '''
 
-        # A handler function for the timer that will raise our custom exception
-        def monitorTimerHandler(signum, frame):
-            raise TimeoutExpiry
+        # Store the default alarm signal so we can set it back again when we're done
+        originalSigHandler = signal.getsignal(signal.SIGALRM)
+        # Ensure that the current signal is not the monitorTimerHandler which would indicate a
+        # recursive call. This is not supported as due to any ongoing alarm timeouts of previous
+        # calls will be be overwritten and we can only have 1 alarm at a time.
+        if originalSigHandler is monitorTimerHandler:
+            raise InvalidContextException("Cannot recursively call doWithTimeout")
 
         # Set up a signal handler that will cause a signal.SIGALRM signal to trigger our timer
         # handler
@@ -377,6 +392,8 @@ def monitorTimerHandler(signum, frame):
         finally:
             # Always turn off the alarm, whether returning a value or propagating an exception
             signal.alarm(0)
+            # Reset the alarm signal handler
+            signal.signal(signal.SIGALRM, originalSigHandler)
 
     def initializeStudioCtxFromArgs(self):
         '''

test/cvlib/context/test_timeout.py

@@ -0,0 +1,31 @@
+# Copyright (c) 2025 Arista Networks, Inc.
+# Use of this source code is governed by the Apache License 2.0
+# that can be found in the COPYING file.
+
+import pytest
+
+from cloudvision.cvlib import Context, InvalidContextException, User
+
+
+def test_do_with_timeout():
+    ctx = Context(user=User("test_user", "123"))
+
+    # Function that is ok to use in a doWithTimeout
+    def okFunc():
+        print("ok")
+
+    # Function that is not ok to use in a doWithTimeout
+    def exceptionFunc():
+        ctx.doWithTimeout(okFunc, 5)
+
+    # Run a function that will pass, though will have set up the
+    # necessary alarms and then unset them
+    ctx.doWithTimeout(okFunc, 5)
+
+    # Run a function that will fail as it is recursively calling doWithTimeout
+    with pytest.raises(InvalidContextException) as exc_info:
+        ctx.doWithTimeout(exceptionFunc, 5)
+    assert "Cannot recursively call doWithTimeout" in str(exc_info.value)
+
+    # Run ok function once again to make sure that previous exception still unset the handler
+    ctx.doWithTimeout(okFunc, 5)