Use semaphore and spinlock in tasking::Scheduler

[mzient]

Category:

Other (e.g. Documentation, Tests, Configuration)

Description:

Separate queue lock

Previously the scheduler featured just one mutex to guard everything. This PR adds a separate lock for the queue of ready tasks. This reduces contention when popping tasks by worker threads.

Use semaphore for queue state tracking

Prior to this change, a condition variable was used to wake up worker threads when ready tasks became available. This PR uses a semaphore which is raised when a task becomes ready and lowered before one is popped.

Additional information:

Affected modules and functionalities:

Key points relevant for the review:

dali/core/exec/tasking_test.cc

• [X] Existing tests apply
• [ ] New tests added
  • [ ] Python tests
  • [X] GTests
  • [ ] Benchmark
  • [ ] Other
• [ ] N/A

Checklist

Documentation

• [ ] Existing documentation applies
• [ ] Documentation updated
  • [ ] Docstring
  • [ ] Doxygen
  • [ ] RST
  • [ ] Jupyter
  • [ ] Other
• [X] N/A

DALI team only

Requirements

• [ ] Implements new requirements
• [ ] Affects existing requirements
• [X] N/A

REQ IDs: N/A

JIRA TASK: N/A

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