Propeller Manual

LOCKSET – Spin Language Reference
Page 126 · Propeller Manual v1.1
LOCKSET
Command: Set lock to true and get its previous state.
((PUB ┆ PRI))
LOCKSET ( ID )
Returns: Previous state of lock (TRUE or FALSE).
•
ID is the ID (0 – 7) of the lock to set to TRUE.
Explanation
LOCKSET is one of four lock commands (T LOCKNEW, LOCKRETT, LOCKSET, and T LOCKCLR) used to
manage resources that are user-defined and deemed mutually exclusive.
LOCKSET sets lock ID
to
TRUE and retrieves the previous state of that lock (TRUE or FALSE).
See About Locks, page 122, and Suggested Rules for Locks, page 123 for information on the
typical use of locks and the
LOCKxxx commands.
The following assumes that a cog (either this one or another) has already checked out a lock
using
LOCKNEW and shared the ID with this cog, which saved it as SemID. It also assumes this
cog has an array of longs called
LocalData.
PUB ReadResource | Idx
repeat until not lockset(SemID) 'wait until we lock the resource
repeat Idx from 0 to 9 'read all 10 longs of resource
LocalData[Idx] := long[Idx]
lockclr(SemID) 'unlock the resource
PUB WriteResource | Idx
repeat until not lockset(SemID) 'wait until we lock the resource
repeat Idx from 0 to 9 'write all 10 longs to resource
long[Idx] := LocalData[Idx]
lockclr(SemID) 'unlock the resource
Both of these methods, ReadResource and WriteResource, follow the same rules before and
after accessing the resource. First, they wait indefinitely at the first
REPEAT loop until it has
locked the resource; i.e., it has successfully “set” the associated lock. If
LOCKSET returns TRUE,
the condition “until not lockset…” is false, meaning that some other cog is currently
accessing the resource, so that first
REPEAT loop tries again. If LOCKSET returns T FALSE, the