NAME

       atomics - Atomic Functions

DESCRIPTION

       This  module  provides  a  set of functions to do atomic operations towards mutable atomic
       variables. The implementation utilizes  only  atomic  hardware  instructions  without  any
       software  level  locking, which makes it very efficient for concurrent access. The atomics
       are organized into arrays with the following semantics:

         * Atomics are 64 bit integers.

         * Atomics can be represented as either signed or unsigned.

         * Atomics wrap around at overflow and underflow operations.

         * All operations guarantee atomicity. No intermediate results can be seen. The result of
           one mutation can only be the input to one following mutation.

         * All  atomic  operations  are  mutually ordered. If atomic B is updated after atomic A,
           then that is how it will appear to any concurrent readers. No one  can  read  the  new
           value of B and then read the old value of A.

         * Indexes  into  atomic  arrays  are  one-based.  An  atomic array of arity N contains N
           atomics with index from 1 to N.

DATA TYPES

       atomics_ref()

              Identifies an atomic array returned from new/2.

EXPORTS

       new(Arity, Opts) -> atomics_ref()

              Types:

                 Arity = integer() >= 1
                 Opts = [Opt]
                 Opt = {signed, boolean()}

              Create a new array of Arity number  of  atomics.  All  atomics  in  the  array  are
              initially set to zero.

              Argument Opts is a list of the following possible options:

                {signed, boolean()}:
                  Indicate  if  the  elements  of the array will be treated as signed or unsigned
                  integers. Default is true (signed).

                  The integer interval for signed atomics are from -(1 bsl 63) to  (1  bsl  63)-1
                  and for unsigned atomics from 0 to (1 bsl 64)-1.

              Atomics are not tied to the current process and are automatically garbage collected
              when they are no longer referenced.

       put(Ref, Ix, Value) -> ok

              Types:

                 Ref = atomics_ref()
                 Ix = Value = integer()

              Set atomic to Value.

       get(Ref, Ix) -> integer()

              Types:

                 Ref = atomics_ref()
                 Ix = integer()

              Read atomic value.

       add(Ref, Ix, Incr) -> ok

              Types:

                 Ref = atomics_ref()
                 Ix = Incr = integer()

              Add Incr to atomic.

       add_get(Ref, Ix, Incr) -> integer()

              Types:

                 Ref = atomics_ref()
                 Ix = Incr = integer()

              Atomic addition and return of the result.

       sub(Ref, Ix, Decr) -> ok

              Types:

                 Ref = atomics_ref()
                 Ix = Decr = integer()

              Subtract Decr from atomic.

       sub_get(Ref, Ix, Decr) -> integer()

              Types:

                 Ref = atomics_ref()
                 Ix = Decr = integer()

              Atomic subtraction and return of the result.

       exchange(Ref, Ix, Desired) -> integer()

              Types:

                 Ref = atomics_ref()
                 Ix = Desired = integer()

              Atomically replaces the value of the atomic with Desired and returns the  value  it
              held previously.

       compare_exchange(Ref, Ix, Expected, Desired) -> ok | integer()

              Types:

                 Ref = atomics_ref()
                 Ix = Expected = Desired = integer()

              Atomically compares the atomic with Expected, and if those are equal, set atomic to
              Desired. Returns ok if Desired was written. Returns the actual atomic value if  not
              equal to Expected.

       info(Ref) -> Info

              Types:

                 Ref = atomics_ref()
                 Info =
                     #{size := Size, max := Max, min := Min, memory := Memory}
                 Size = integer() >= 0
                 Max = Min = integer()
                 Memory = integer() >= 0

              Return information about an atomic array in a map. The map has the following keys:

                size:
                  The number of atomics in the array.

                max:
                  The highest possible value an atomic in this array can hold.

                min:
                  The lowest possible value an atomic in this array can hold.

                memory:
                  Approximate memory consumption for the array in bytes.