// Locks a table in exclusive mode.
func (tr *Transaction) ELock(t *table.Table) int {
existingLocks, status := LocksOf(t)
if status != st.OK {
return status
}
// Do not lock if other transaction(s) have shared or exclusively locked the table.
if (existingLocks.Exclusive != 0 && existingLocks.Exclusive != tr.id) ||
(len(existingLocks.Shared) == 1 && existingLocks.Shared[0] != tr.id) ||
(len(existingLocks.Shared) > 1) {
return st.CannotLockInExclusive
}
// Release previously acquired shared lock, if any.
if len(existingLocks.Shared) == 1 && existingLocks.Shared[0] == tr.id {
status = tr.unlock(t)
if status != st.OK {
return status
}
}
// Create exclusive lock file.
status = util.CreateAndWrite(t.Path+t.Name+".exclusive", tr.ID)
if status != st.OK {
return status
}
tr.Locked = append(tr.Locked[:], t)
return st.OK
}
func (tr *Transaction) SLock(t *table.Table) int {
existingLocks, status := LocksOf(t)
if status != st.OK {
return status
}
// Do not lock if another transaction has locked the table exclusively.
if existingLocks.Exclusive != 0 && existingLocks.Exclusive != tr.id {
return st.CannotLockInShared
}
// Release previously acquired exclusive lock, if any.
if existingLocks.Exclusive == tr.id {
status = tr.unlock(t)
if status != st.OK {
return status
}
}
// Create shared lock file.
status = util.CreateAndWrite(t.Path+t.Name+".shared/"+tr.ID, "")
if status != st.OK {
return status
}
tr.Locked = append(tr.Locked[:], t)
return st.OK
}