Last edited by
KK on 18-Dec-81 13:41:01
MBrown on January 21, 1983 4:43 pm
Taft on September 30, 1982 3:01 pm
Hauser, May 20, 1985 11:10:09 am PDT
Bob Hagmann March 24, 1988 3:45:47 pm PST
LockID: TYPE = YggInternal.LockID;
LockSubID: TYPE = YggInternal.LockSubID;
nullLockID: LockID = YggInternal.nullLockID;
A file is a typical entity; a sub entity of a file is a page, the file's length, etc. If consecutive pages are represented as consecutive sub entities, then the lock manager may use a run-encoded representation. An application may use the entity field to encode what it thinks of as types: "database record", "index value", etc. The sub entity field must then be used to encode the name of a specific object of that type: a particular record or index value.
Since lock mangers are responsible for locking disjoint sets of entities, there is no need for LockIDs to be unique across lock managers, much less across all space and time. They aren't unique IDs in the strongest sense.
LockMode: TYPE = YggEnvironment.LockMode;
Set:
PROC [
trans: YggInternal.TransHandle, lock: LockID, mode: LockMode, wait: BOOL ← FALSE]
RETURNS [resultMode: LockMode];
! Failed {conflict, timeout}, TransAborting;
Caller must have started work for trans.
Acquires lock, in lock mode mode, for transaction trans. Returns the mode in which
the lock is now held by this transaction.
If the lock cannot immediately be aquired because a conflicting lock is already set
by another transaction, and wait=FALSE, raises Failed[conflict]. If wait=TRUE, waits
until the lock can be acquired. Raises Failed[timeout] if this wait is too long.
If transaction trans is selected to be aborted while a Set call is waiting, Set raises
TransAborting. Trans is not yet aborted, but the caller should abort the operation
in progress.
ModeReleasableSet: TYPE = PACKED ARRAY LockMode OF ModeReleasable;
ModeReleasable: TYPE = {no, yes} ← no;
Release:
PROC [trans: YggInternal.TransHandle, lock: LockID,
releasable: ModeReleasableSet ← [read: yes]] RETURNS [LockMode];
! Error {lockUnreleasable, unknown};
Releases a lock previously set by the same transaction if the lock's current mode
is a member of the specified releasable set.
Locks for a given LockID are counted, so the lock is actually released only if there
have been as many Unlocks as there have been Locks.
Note that the lock's mode remains at the strongest value reached during its lifetime;
there is no way to downgrade an individual lock short of releasing it altogether.
Returns none if the lock was released, otherwise returns the mode in which the
lock is held by this transaction.
Raises Error[unknown] if trans has not previously set lock.
Raises Error[lockUnreleasable] if trans has previously set lock in an unreleasable mode.
ReleaseFileLocks:
PROC [trans: YggInternal.TransHandle, prototype: LockID, releasable: ModeReleasableSet];
Releases locks previously set by the transaction on the file specified in the prototype which also have current mode in the specified releasable set. Both entire-file and page locks are released. Lock counts are ignored. Intended use is immediately following commit and continue to release unneeded files.
Compat:
READONLY
ARRAY LockMode
OF
PACKED
ARRAY LockMode
OF
BOOL;
Compatibility predicate: Compat[r][e] is TRUE iff a request r is compatible
with a granted lock e for another transaction.
Sup:
READONLY
ARRAY LockMode
OF
PACKED
ARRAY LockMode
OF LockMode;
Supremem relation: Sup[r][e] is the supremum of r and e in the partial ordering of
lock modes. That is, if mode r is requested for an object already locked in mode e
by the same transaction, the object will actually be locked in the mode Sup[r][e].
Error: ERROR [type: ErrorType];
ErrorType: TYPE = {lockUnreleasable, unknown};
Failed:
ERROR [why: YggEnvironment.LockFailure];
{conflict, timeout}
TransAborting: ERROR;
END.