Macro: SB-EXT:COMPARE-AND-SWAP

Atomically stores NEW in PLACE if OLD matches the current value of PLACE. Two values are considered to match if they are EQ. Returns the previous value of PLACE: if the returned value is EQ to OLD, the swap was carried out.

PLACE must be an CAS-able place. Built-in CAS-able places are accessor forms whose CAR is one of the following:

CAR, CDR, FIRST, REST, SVREF, SYMBOL-PLIST, SYMBOL-VALUE, SVREF, SLOT-VALUE SB-MOP:STANDARD-INSTANCE-ACCESS, SB-MOP:FUNCALLABLE-STANDARD-INSTANCE-ACCESS,

or the name of a DEFSTRUCT created accessor for a slot whose declared type is either FIXNUM or T. Results are unspecified if the slot has a declared type other than FIXNUM or T.

In case of SLOT-VALUE, if the slot is unbound, SLOT-UNBOUND is called unless OLD is EQ to SB-PCL:+SLOT-UNBOUND+ in which case SB-PCL:+SLOT-UNBOUND+ is returned and NEW is assigned to the slot. Additionally, the results are unspecified if there is an applicable method on either SB-MOP:SLOT-VALUE-USING-CLASS, (SETF SB-MOP:SLOT-VALUE-USING-CLASS), or SB-MOP:SLOT-BOUNDP-USING-CLASS.

Additionally, the PLACE can be a anything for which a CAS-expansion has been specified using DEFCAS, DEFINE-CAS-EXPANDER, or for which a CAS-function has been defined. (See SB-EXT:CAS for more information.)

Lambda list

(sb-impl::place sb-impl::old sb-impl::new)