RC PF_FileHandle::AllocatePage (PF_PageHandle &pageHandle) {
if (!bOpen) {
return PF_FHCLOSED;
}
PageNum i;
/* Search for a free page using the PF header */
for (i = 1; i <= pageCount; i++) {
if (GetPageType(i) == FREE_PAGE) {
break;
}
}
/* If increasing file size exceeds limit, return error */
if (i >= 8*(PF_PAGE_SIZE-PF_FILESUBHDR_SIZE)) {
return PF_DBFULL;
}
Frame *pFrame;
RC rc;
/* If the paged file has no free pages, increase the file size */
if (i > pageCount) {
/* Increment page count */
pageCount += 1;
/* Request buffer space for writing a page to disk */
rc = bfm.Alloc (fileName, i, fileDesc, pFrame);
if (rc != SUCCESS) {
pageCount -= 1;
return rc;
}
/* Append page to file */
rc = bfm.WritePage (fileDesc, *pFrame);
if (rc != SUCCESS) {
bfm.Free (pFrame);
pageCount -= 1;
return rc;
}
}
else {
/* Allocated buffer space */
rc = bfm.Alloc (fileName, i, fileDesc, pFrame);
if (rc != SUCCESS) {
bfm.Free (pFrame);
return rc;
}
}
/* Do not reverse the order of these operations as only
* SetPageType() writes the updated header to disk */
/* Update sub-header information */
fileSubHeader.nAllocatedPages++;
/* Update bitmap */
SetPageType (i, ALLOCATED_PAGE);
/* Open page handle */
rc = pageHandle.Open (*pFrame);
if (rc != SUCCESS) {
return rc;
}
return SUCCESS;
}
RC PF_FileHandle::GetThisPage (PageNum pageNum, PF_PageHandle &pageHandle) const {
if (!bOpen) {
return PF_FHCLOSED;
}
if (pageNum < 1
|| pageNum > pageCount
|| GetPageType(pageNum) == FREE_PAGE) {
return PF_INVALIDPAGENUM;
}
Frame *pFrame;
RC rc;
/* Find frame in buffer that correspods to
the given filename and page number */
rc = bfm.Find (fileName, pageNum, pFrame);
if (rc == SUCCESS) { /* If page is found in buffer, increment pin count */
pFrame->pinCount++;
}
else { /* If page is not found in buffer, fetch it from disk */
/* Request buffer space */
rc = bfm.Alloc (fileName, pageNum, fileDesc, pFrame);
if (rc != SUCCESS) {
return rc;
}
/* Fetch page from disk */
rc = bfm.ReadPage (fileDesc, *pFrame);
if (rc != SUCCESS) {
bfm.Free (pFrame);
return rc;
}
}
/* pFrame now points to the frame containing the request page.
We return a page handle to it. */
return pageHandle.Open (*pFrame);
}
