Notes_ACID_and_Concurrency.txt

ACID Properties and Concurrency (summary)
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Atomicity
- Financial operations (transfers, loan disbursement, payments) are implemented as single procedures.
- Where multiple file updates are required, the code uses temporary files and renames (atomic replace) to avoid partial writes.

Consistency
- Input validation is applied before any transaction (balances, account existence, etc).
- CSV format expectations are enforced by parsers; malformed lines are skipped with logging.

Isolation
- File-level locking is used when updating shared CSV files to prevent race conditions.
- The project uses POSIX file locks (flock or fcntl) in utils/session_manager functions to ensure that concurrent processes do not interleave writes.

Durability
- After successful operations, data is flushed to disk using fsync or file close semantics to ensure the OS writes are committed.
- The project keeps transactions.csv as the audit trail for recovery.

Concurrency & Synchronization
- The codebase contains helper functions (in utils.c / session_manager.c) for acquiring and releasing locks around critical sections when accessing data files.
- For multi-step operations, locks are held for the minimum required time and released promptly.
- The design favors fail-safe behavior: if an operation cannot acquire the lock, it either retries or returns an error to the caller for retry.

Notes & Caveats
- The above describes standard approaches; please review the relevant functions in utils.c and session_manager.c for exact implementations and any platform-specific behavior.
- If you require a formal proof or instrumentation logs demonstrating concurrency under load, I can run tests and add them to the package.