rwlock_destroy Syntax

#include <synch.h>  (or #include <thread.h>)

int rwlock_destroy(rwlock_t *rwlp);

The space for storing the read-write lock is not freed. For POSIX threads, see pthread_rwlock_destroy Syntax.

Example 6–1 uses a bank account to demonstrate read-write locks. While the program could allow multiple threads to have concurrent read-only access to the account balance, only a single writer is allowed. Note that the get_balance() function needs the lock to ensure that the addition of the checking and saving balances occurs atomically.

Example 6–1 Read-Write Bank Account

rwlock_t account_lock;
float checking_balance = 100.0;
float saving_balance = 100.0;
...
rwlock_init(&account_lock, 0, NULL);
...

float
get_balance() {
    float bal;

    rw_rdlock(&account_lock);
    bal = checking_balance + saving_balance;
    rw_unlock(&account_lock);
    return(bal);
}

void
transfer_checking_to_savings(float amount) {
    rw_wrlock(&account_lock);
    checking_balance = checking_balance - amount;
    saving_balance = saving_balance + amount;
    rw_unlock(&account_lock);
}