//growing phase
for (int index : sorted_transaction) {
Row &row = table[index];
row.lock.lock();
}
//critical section
for (int index : random_transaction) {
Row &row = table[index];
int row_data = row.getData();
row_data += 1;
row.setData(row_data);
}
//shrinking phase
for (int index : sorted_transaction) {
Row &row = table[index];
row.lock.unlock();
}
Rust Attempt
let mut acquired_locks: Vec<&MutexGuard<i32>> = Vec::new();
// sort phase
sorted_readset.rdxsort();
// growing phase
for index in sorted_readset {
let u_index = index as usize;
let row = &table[u_index];
let guard = row.lock.lock().unwrap();
acquired_locks.push(&guard);
}
//critical section
for index in random_readset {
let u_index = index as usize;
let mut row = &mut table[u_index];
row.value = row.value + 1;
}
//since this will become out of scope, it'll automatically shrink
As you can see, it's impossible since the Mutex is immediately released after exiting the loop, once ownership is released. I attempted to transfer ownership by appending it to a vector. That throws an error since the lockguard is a borrowed value.
You should iterate the Mutexes by reference, and hold the MutexGuards by value. Your actual mutations should also happen through the guards, because unlike C++, Mutex directly wraps its protected values.
As an aid to future seaches on this and related topics, would you consider revising the title of this thread from its current definitive-but-incorrect statement to something like "Help implementing 2-phase locking in Rust". As you can see from @cuviper's response, it is not impossible to implement 2-phase locking in Rust; it's just that the approach differs from that in C++.
You should be able to put the guard into a vector, but the vector must take ownership by having the type Vec<MutexGuard<i32>> since otherwise the guard is dropped at the end of the body of the for loop, invalidating the reference to it you put in the vector.
Thanks everyone. Actually just new to Rust. So, I solved the problem of storing the MutexGuards. I'm running into a different problem hehehehehe should be a different thread. Thanks for all your help
I can't iterate through the mutexes by references since I need to modify them during the critical phase... Keeping hold of the mutexes as mutable references in a loop throws an error.
