atomics(3erl) Erlang Module Definition atomics(3erl)
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 hard-
ware 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 fol-
lowing 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 atomic array of Arity atomics.
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 automati-
cally 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 re-
turns 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.
Ericsson AB erts 11.0.2 atomics(3erl)