gxDatabaseError BtreeCache::LRUFlush(unsigned num_to_flush)
// Function used to flush a specified number of least recently
// used (LRU) dirty buckets. Returns zero if successful or a
// non-zero value to indicate a failure.
{
if((f == 0) || (buckets == 0)) return gxDBASE_NULL_PTR;
// Flush, starting at the tail so that cache will be flushed
// in a first in, first out sequence (FIFO)
BtreeBucket *bucket = tail;
unsigned num_flushed = 0;
// PC-lint 04/20/2004: Possible use ot null pointer
if(!bucket) return gxDBASE_NULL_PTR;
while(1) {
if(num_flushed == num_to_flush) break;
if(f->ReadyForWriting()) {
if(bucket->Flush(f) != gxDBASE_NO_ERROR) {
return f->GetDatabaseError(); // Error writing to the file
}
}
else { // The file is not ready for writing
return f->SetDatabaseError(gxDBASE_FILE_NOT_READY);
}
bucket = bucket->prev;
if(bucket == tail) break; // Reached the end of the list
num_flushed++;
}
return gxDBASE_NO_ERROR;
}
gxDatabaseError BtreeCache::Flush()
// Function used to flush all the dirty buckets to the database file.
// Returns zero if successful or a non-zero value to indicate
// a failure.
{
if((f == 0) || (buckets == 0)) return gxDBASE_NULL_PTR;
// Flush, starting at the front so that cache will be flushed
// in a first in, last out sequence
BtreeBucket *bucket = head;
// PC-lint 04/20/2004: Possible use of null pointer
if(!bucket) return gxDBASE_NULL_PTR;
do {
if(f->ReadyForWriting()) {
if(bucket->Flush(f) != gxDBASE_NO_ERROR) {
return f->GetDatabaseError(); // Error writing to the file
}
}
else { // The file is not ready for writing
return f->SetDatabaseError(gxDBASE_FILE_NOT_READY);
}
bucket = bucket->next;
} while(bucket != head);
return gxDBASE_NO_ERROR;
}
BtreeBucket *BtreeCache::FindEmptyBucket()
// Internal processing function used to find the last
// bucket in the cache that is empty and promote the
// bucket to the front of the list. Returns a pointer
// to the bucket or a null value if no buckets can be
// made available or an error occurs. For maximum speed
// performance the least-recently reserved bucket will
// be always be flushed and re-allocated to prevent the
// cache from filling up.
{
if(IsEmpty()) {
// Set the database error code here to ensure that an
// exception is properly signaled in the gxBtree
// cached insert, delete, and find functions.
if(f) f->SetDatabaseError(gxDBASE_CACHE_ERROR);
return 0;
}
BtreeBucket *bucket = tail;
// PC-lint 04/20/2004: Possible use of null pointer
if(!bucket) return 0;
if(f) { // PC-lint 04/20/2004: Possible use of null pointer
if(f->ReadyForWriting()) {
if(bucket->Flush(f) != gxDBASE_NO_ERROR) {
return 0; // Error writing to the file
}
}
else { // The file is not ready for writing
f->SetDatabaseError(gxDBASE_FILE_NOT_READY);
return 0;
}
}
PromoteBucket(bucket);
return bucket;
}