System.AtomicCmpExchange
Delphi
function AtomicCmpExchange(var Target: Integer; NewValue: Integer; Comparand: Integer): Integer; overload;
function AtomicCmpExchange(var Target: Int64; NewValue: Int64; Comparand: Int64): Int64; overload;
function AtomicCmpExchange(var Target: Pointer; NewValue: Pointer; Comparand: Pointer): Pointer; overload;
function AtomicCmpExchange(var Target: Integer; NewValue: Integer; Comparand: Integer; out Succeeded: Boolean): Integer; overload;
function AtomicCmpExchange(var Target: Int64; NewValue: Int64; Comparand: Int64; out Succeeded: Boolean): Int64; overload;
function AtomicCmpExchange(var Target: Pointer; NewValue: Pointer; Comparand: Pointer; out Succeeded: Boolean): Pointer; overload;
Properties
| Type | Visibility | Source | Unit | Parent |
|---|---|---|---|---|
| function | public | System.pas | System | System |
Description
Atomic intrinsic Compare and Exchange function compares the contents of the Target to a given value (Comparand) and, only if they are the same, modifies the contents of Target to the new value.
This function always returns the original value of Target. If a Succeeded parameter is provided, Succeeded becomes True if there is a value exchange (even if both Target and NewValue are the same); it becomes False otherwise.
The System unit provides four atomic intrinsic functions that provide a way to atomically exchange, compare and exchange, increment, and decrement memory values.
AtomicCmpExchange is used for comparing and exchanging memory values.
Atomic operations are used to:
- Implement multi-threaded locking primitives
- Provide the primitives necessary for implementing so-called "lock-free" structures
Sample Code
program SystemAtomicCmpExchange;
{$APPTYPE CONSOLE}
{$R *.res}
uses
System.SysUtils, Winapi.Windows;
var
Target,
Comparand,
Return : Integer;
Succeeded : Boolean;
const
ReplaceValue = Integer(5);
begin
try
WriteLn('System.AtomicCmpExchange');
WriteLn;
Target := 1;
Comparand := 0;
WriteLn(Format('Initial values: Target: %d, Comparand: %d, ReplaceValue : %d',
[Target, Comparand, ReplaceValue]));
Return := System.AtomicCmpExchange(Target, ReplaceValue, Comparand, Succeeded);
WriteLn(Format('After calling: Target: %d, Comparand: %d, Return: %d, Succeeded: %s',
[Target, Comparand, Return, BoolToStr(Succeeded, true)]));
WriteLn;
Target := 1;
Comparand := 1;
WriteLn(Format('Initial values: Target: %d, Comparand: %d, ReplaceValue : %d',
[Target, Comparand, ReplaceValue]));
Return := System.AtomicCmpExchange(Target, ReplaceValue, Comparand, Succeeded);
WriteLn(Format('After calling: Target: %d, Comparand: %d, Return: %d, Succeeded: %s',
[Target, Comparand, Return, BoolToStr(Succeeded, true)]));
WriteLn;
WriteLn('InterlockedCompareExchange');
WriteLn;
Target := 1;
Comparand := 0;
WriteLn(Format('Initial values: Target: %d, Comparand: %d, ReplaceValue : %d',
[Target, Comparand, ReplaceValue]));
Return := InterlockedCompareExchange(Target, ReplaceValue, Comparand);
WriteLn(Format('After calling: Target: %d, Comparand: %d, Return: %d',
[Target, Comparand, Return]));
WriteLn;
Target := 1;
Comparand := 1;
WriteLn(Format('Initial values: Target: %d, Comparand: %d, ReplaceValue : %d',
[Target, Comparand, ReplaceValue]));
Return := InterlockedCompareExchange(Target, ReplaceValue, Comparand);
WriteLn(Format('After calling: Target: %d, Comparand: %d, Return: %d',
[Target, Comparand, Return]));
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
end.