atomics (erts v12.0.3)
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.
Link to this section Summary
Functions
Add Incr to atomic.
Atomic addition and return of the result.
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.
Atomically replaces the value of the atomic with Desired and returns the value it held previously.
Read atomic value.
Return information about an atomic array in a map. The map has the following keys
Create a new array of Arity number of atomics. All atomics in the array are initially set to zero.
Set atomic to Value.
Subtract Decr from atomic.
Atomic subtraction and return of the result.
Link to this section Types
Specs
atomics_ref()
Identifies an atomic array returned from new/2.
Link to this section Functions
Specs
add(Ref, Ix, Incr) -> ok when Ref :: atomics_ref(), Ix :: integer(), Incr :: integer().
Add Incr to atomic.
Specs
add_get(Ref, Ix, Incr) -> integer() when Ref :: atomics_ref(), Ix :: integer(), Incr :: integer().
Atomic addition and return of the result.
Specs
compare_exchange(Ref, Ix, Expected, Desired) -> ok | integer()
when
Ref :: atomics_ref(),
Ix :: integer(),
Expected :: integer(),
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.
Specs
exchange(Ref, Ix, Desired) -> integer()
when Ref :: atomics_ref(), Ix :: integer(), Desired :: integer().
Atomically replaces the value of the atomic with Desired and returns the value it held previously.
Specs
get(Ref, Ix) -> integer() when Ref :: atomics_ref(), Ix :: integer().
Read atomic value.
Specs
info(Ref) -> Info
when
Ref :: atomics_ref(),
Info :: #{size := Size, max := Max, min := Min, memory := Memory},
Size :: non_neg_integer(),
Max :: integer(),
Min :: integer(),
Memory :: non_neg_integer().
Return information about an atomic array in a map. The map has the following keys:
sizeThe number of atomics in the array.
maxThe highest possible value an atomic in this array can hold.
minThe lowest possible value an atomic in this array can hold.
memoryApproximate memory consumption for the array in bytes.
Specs
new(Arity, Opts) -> atomics_ref() when Arity :: pos_integer(), 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)-1and for unsigned atomics from0to(1 bsl 64)-1.
Atomics are not tied to the current process and are automatically garbage collected when they are no longer referenced.
Specs
put(Ref, Ix, Value) -> ok when Ref :: atomics_ref(), Ix :: integer(), Value :: integer().
Set atomic to Value.
Specs
sub(Ref, Ix, Decr) -> ok when Ref :: atomics_ref(), Ix :: integer(), Decr :: integer().
Subtract Decr from atomic.
Specs
sub_get(Ref, Ix, Decr) -> integer() when Ref :: atomics_ref(), Ix :: integer(), Decr :: integer().
Atomic subtraction and return of the result.