Fix destructor related test errors and adding Redis exception handling in PSUd

[GauravNagesh]

Description

This PR addresses two related fixes in the PSUd module:

1. Exception Handling for Redis DB Calls - Wrapped Redis interactions in try-except blocks to handle potential exceptions, such as connection issues or missing keys. This improves the robustness of the application and prevents unexpected crashes due to Redis unavailability.

2. Fix Errors in DaemonPsud Object Destruction During Tests - Resolved test errors that occurred when objects were garbage collected and their destructors attempted to delete missing Redis keys. The del method is now mocked, ensuring clean test teardown without unhandled exceptions.

Motivation and Context

Previously, if there was a temporary failure during the initial Redis connection to STATE_DB, table creation, or any Redis write/set operation, the daemon would crash instead of handling the error gracefully.
With this update:

• If initialization fails, the daemon will now exit gracefully with appropriate logging.
• If a Redis set or write operation fails during runtime, the error will be logged, and the operation will be retried in the next daemon cycle.

Additionally, during testing, when the DaemonPsud object is garbage collected, its destructor method __del__ is invoked. At that point, it attempts to delete keys from the mock Redis tables (psu_tbl and chassis_tbl). However, since these keys may not exist in the mocked environment, it results in a KeyError, as shown below:

  Traceback (most recent call last):
    File "/__w/1/s/sonic-psud/scripts/psud", line 419, in __del__
      self.psu_tbl._del(get_psu_key(psu_index))
    File "/__w/1/s/sonic-psud/tests/mocked_libs/swsscommon/swsscommon.py", line 16, in _del
      del self.mock_dict[key]
          ~~~~~~~~~~~~~~^^^^^
  KeyError: 'PSU 1'

  Traceback (most recent call last):
    File "/__w/1/s/sonic-psud/scripts/psud", line 422, in __del__
      self.chassis_tbl._del(CHASSIS_INFO_POWER_KEY_TEMPLATE.format(1))
    File "/__w/1/s/sonic-psud/tests/mocked_libs/swsscommon/swsscommon.py", line 16, in _del
      del self.mock_dict[key]
          ~~~~~~~~~~~~~~^^^^^
  KeyError: 'chassis_power_budget 1'

Both of these errors are currently visible in the pipeline.

How Has This Been Tested?

Tested locally to confirm that initialization failures are handled gracefully and that destructor-related key deletion no longer raises errors.

Additional Information (Optional)

[mssonicbld]

/azp run

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[mssonicbld]

/azp run

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[GauravNagesh]

/azpw run

[mssonicbld]

/AzurePipelines run

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[Copilot]

Pull request overview

This PR enhances the robustness of the PSUd daemon by adding comprehensive exception handling for Redis database operations and fixing destructor-related test failures. The changes ensure that Redis connection issues or missing keys don't cause unexpected crashes during normal operation or test garbage collection.

• Added try-except blocks around all Redis database operations (table.set, table._del) with appropriate error logging
• Wrapped database initialization in exception handling with graceful exit on failure
• Mocked __del__ method in tests to prevent KeyError exceptions during garbage collection
• Added comprehensive test coverage for all new exception handling paths

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 8 comments.

File	Description
sonic-psud/scripts/psud	Added exception handling for Redis operations in initialization, destructor, and all table update methods
sonic-psud/tests/test_psud.py	Mocked __del__ method to prevent garbage collection issues
sonic-psud/tests/test_DaemonPsud.py	Added tests for exception handling in initialization, destructor, and update methods; mocked __del__
sonic-psud/tests/test_PsuChassisInfo.py	Added test for exception handling in power budget update

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[Copilot]

The expression exit_code+2 is incorrect. Since exit_code is a global variable initialized to 0 and only modified in the signal handler, this will always evaluate to 2. Either use the constant 2 directly, or define a named constant like DB_CONNECTION_ERROR = 2 at the module level (similar to PSUUTIL_LOAD_ERROR = 1) for clarity and consistency.

[GauravNagesh]

Done

[Copilot]

The test expects sys.exit(2) to be called, but the implementation calls sys.exit(exit_code+2). Since exit_code is 0 by default, this happens to work, but if the test setup changes the global exit_code, this assertion will fail. The test should either verify the actual implementation behavior or the implementation should be fixed to use a constant.

[GauravNagesh]

Done

[Copilot]

Remove the commented-out code. If this line is not needed, it should be deleted rather than left as a comment.

Suggested change

# mock_fan.get_name = mock.Mock(return_value="PSU 1 Test Fan 1")

[GauravNagesh]

Done

[Copilot]

The del special method is called explicitly.

[GauravNagesh]

Writing it as del daemon_psud will not that guarantee that the python's garbage collector will invoke the object's __del__ method during the execution of this testcase itself. Therefore, calling __del__() explicitly ensures deterministic execution of the cleanup logic for testing purposes.

[Copilot]

The del special method is called explicitly.

[GauravNagesh]

Writing it as del daemon_psud will not that guarantee that the python's garbage collector will invoke the object's __del__ method during the execution of this testcase itself. Therefore, calling __del__() explicitly ensures deterministic execution of the cleanup logic for testing purposes.

[Copilot]

Variable daemon_psud is not used.

Suggested change

	daemon_psud = psud.DaemonPsud(SYSLOG_IDENTIFIER)
	psud.DaemonPsud(SYSLOG_IDENTIFIER)

[GauravNagesh]

Done

[Copilot]

This assignment to 'daemon_psud' is unnecessary as it is redefined before this value is used.

Suggested change

	daemon_psud = psud.DaemonPsud(SYSLOG_IDENTIFIER)
	psud.DaemonPsud(SYSLOG_IDENTIFIER)

[GauravNagesh]

Done

[Copilot]

Call to MockPsu.init with too many arguments; should be no more than 0.
Call to MockPsu.init with too many arguments; should be no more than 0.

[GauravNagesh]

The MockPsu constructor does allow to pass these arguments and similar instantiations are used elsewhere in this file and other test files without any issues.

[mssonicbld]

/azp run

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Azure Pipelines successfully started running 1 pipeline(s).