In the course of multi-processing, it is important to ensure that two processes do not modify the same data simultaneously. This is done by creating a lock, which is an extra memory location in a data structure that can be checked to determine whether that structure is in use. If the value of a lock is nil , no process is using the data structure; otherwise, the value should be a process that is currently using the structure.
The following symbols for creating locks will work with all CLIM ports.
with-lock-held [Macro]
Arguments: (place
&optional
state)
&body
body
Summary: Evaluates body with the lock named by place . place is a reference to a lock created by make-lock . state specifies the process to store in the place location; the default value is the value of the variable *current-process* .
On systems that do not support locking, with-lock-held is equivalent to progn .
make-lock [Function]
Summary: Creates a lock whose name is name . On systems that do not support locking, this will return a new list of one element, nil .
with-recursive-lock-held [Macro]
Arguments: (place
&optional
state)
&body
body
Summary: Evaluates body with the recursive lock named by place . place is a reference to a recursive lock created by make-recursive-lock . A recursive lock differs from an ordinary lock in that a process that already holds the recursive lock can call with-recursive-lock-held on the same lock without blocking.
On systems that do not support locking, with-recursive-lock-held is equivalent to progn .
make-recursive-lock [Function]
Summary: Creates a recursive lock whose name is name . On systems that do not support locking, this will return a new list of one element, nil .