Account Locking (Read/Write)

The mechanism by which Solana's scheduler reserves access to accounts for the duration of a transaction's execution, granting either shared read locks (multiple transactions can hold simultaneously) or exclusive write locks (only one transaction at a time). Before execution, the runtime inspects every transaction's declared account list and grants or denies locks accordingly, preventing data races without requiring a global mutex. Transactions that cannot acquire all required locks are queued or dropped, making correct account declaration in transaction instructions critical for both correctness and landing probability.