Concurrency

Atom

• An atom can be modified
• Although they can be modified, they are thread-safe
• The value of an atom can be accessed with @

Swap

• The swap! function changes the value of an atom
• All other function that modifies an atom must have ! in its name
• Functions that modify the value of atom are functions with side effects

Retry

• If an atom changes while a function that accesses it is running, this function is rerun
• Also before updating an atom (swap), it is checked whether the atom has been changed before. If yes, the whole function is rerun
• The retry function must be as simple as possible!
• Therefore, functions that access an atom are performed as a transaction
• The retry mechanism is implemented instead of using traditional locks

Reference

• Differs from an atom in a way that it allows transactions with multiple mutable elements
• The atom itself do not allow changes from multiple atoms in the same function
• Perform changes with the help of transactions with the function dosync.
• All operations inside a transaction are performed together, or none of them is performed

Future

• Returns a promise of a result in the future
• Futures are executed in a parallel thread and do not block the current thread!
• Futures can resolve or fail