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author | EuAndreh <eu@euandre.org> | 2024-10-26 13:24:52 -0300 |
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committer | EuAndreh <eu@euandre.org> | 2024-10-26 13:24:52 -0300 |
commit | c7e2dea6f6148d0972c0b1f2795910c9a24ac27a (patch) | |
tree | 9dbcd8906cb8421b08cf3d91ead7e43b30077231 /src/freelist.go | |
parent | Move code to src/ and tests/ (diff) | |
download | dedo-c7e2dea6f6148d0972c0b1f2795910c9a24ac27a.tar.gz dedo-c7e2dea6f6148d0972c0b1f2795910c9a24ac27a.tar.xz |
Normalize structure following other projects
Diffstat (limited to 'src/freelist.go')
-rw-r--r-- | src/freelist.go | 252 |
1 files changed, 0 insertions, 252 deletions
diff --git a/src/freelist.go b/src/freelist.go deleted file mode 100644 index aba48f5..0000000 --- a/src/freelist.go +++ /dev/null @@ -1,252 +0,0 @@ -package bolt - -import ( - "fmt" - "sort" - "unsafe" -) - -// freelist represents a list of all pages that are available for allocation. -// It also tracks pages that have been freed but are still in use by open transactions. -type freelist struct { - ids []pgid // all free and available free page ids. - pending map[txid][]pgid // mapping of soon-to-be free page ids by tx. - cache map[pgid]bool // fast lookup of all free and pending page ids. -} - -// newFreelist returns an empty, initialized freelist. -func newFreelist() *freelist { - return &freelist{ - pending: make(map[txid][]pgid), - cache: make(map[pgid]bool), - } -} - -// size returns the size of the page after serialization. -func (f *freelist) size() int { - n := f.count() - if n >= 0xFFFF { - // The first element will be used to store the count. See freelist.write. - n++ - } - return pageHeaderSize + (int(unsafe.Sizeof(pgid(0))) * n) -} - -// count returns count of pages on the freelist -func (f *freelist) count() int { - return f.free_count() + f.pending_count() -} - -// free_count returns count of free pages -func (f *freelist) free_count() int { - return len(f.ids) -} - -// pending_count returns count of pending pages -func (f *freelist) pending_count() int { - var count int - for _, list := range f.pending { - count += len(list) - } - return count -} - -// copyall copies into dst a list of all free ids and all pending ids in one sorted list. -// f.count returns the minimum length required for dst. -func (f *freelist) copyall(dst []pgid) { - m := make(pgids, 0, f.pending_count()) - for _, list := range f.pending { - m = append(m, list...) - } - sort.Sort(m) - mergepgids(dst, f.ids, m) -} - -// allocate returns the starting page id of a contiguous list of pages of a given size. -// If a contiguous block cannot be found then 0 is returned. -func (f *freelist) allocate(n int) pgid { - if len(f.ids) == 0 { - return 0 - } - - var initial, previd pgid - for i, id := range f.ids { - if id <= 1 { - panic(fmt.Sprintf("invalid page allocation: %d", id)) - } - - // Reset initial page if this is not contiguous. - if previd == 0 || id-previd != 1 { - initial = id - } - - // If we found a contiguous block then remove it and return it. - if (id-initial)+1 == pgid(n) { - // If we're allocating off the beginning then take the fast path - // and just adjust the existing slice. This will use extra memory - // temporarily but the append() in free() will realloc the slice - // as is necessary. - if (i + 1) == n { - f.ids = f.ids[i+1:] - } else { - copy(f.ids[i-n+1:], f.ids[i+1:]) - f.ids = f.ids[:len(f.ids)-n] - } - - // Remove from the free cache. - for i := pgid(0); i < pgid(n); i++ { - delete(f.cache, initial+i) - } - - return initial - } - - previd = id - } - return 0 -} - -// free releases a page and its overflow for a given transaction id. -// If the page is already free then a panic will occur. -func (f *freelist) free(txid txid, p *page) { - if p.id <= 1 { - panic(fmt.Sprintf("cannot free page 0 or 1: %d", p.id)) - } - - // Free page and all its overflow pages. - var ids = f.pending[txid] - for id := p.id; id <= p.id+pgid(p.overflow); id++ { - // Verify that page is not already free. - if f.cache[id] { - panic(fmt.Sprintf("page %d already freed", id)) - } - - // Add to the freelist and cache. - ids = append(ids, id) - f.cache[id] = true - } - f.pending[txid] = ids -} - -// release moves all page ids for a transaction id (or older) to the freelist. -func (f *freelist) release(txid txid) { - m := make(pgids, 0) - for tid, ids := range f.pending { - if tid <= txid { - // Move transaction's pending pages to the available freelist. - // Don't remove from the cache since the page is still free. - m = append(m, ids...) - delete(f.pending, tid) - } - } - sort.Sort(m) - f.ids = pgids(f.ids).merge(m) -} - -// rollback removes the pages from a given pending tx. -func (f *freelist) rollback(txid txid) { - // Remove page ids from cache. - for _, id := range f.pending[txid] { - delete(f.cache, id) - } - - // Remove pages from pending list. - delete(f.pending, txid) -} - -// freed returns whether a given page is in the free list. -func (f *freelist) freed(pgid pgid) bool { - return f.cache[pgid] -} - -// read initializes the freelist from a freelist page. -func (f *freelist) read(p *page) { - // If the page.count is at the max uint16 value (64k) then it's considered - // an overflow and the size of the freelist is stored as the first element. - idx, count := 0, int(p.count) - if count == 0xFFFF { - idx = 1 - count = int(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[0]) - } - - // Copy the list of page ids from the freelist. - if count == 0 { - f.ids = nil - } else { - ids := ((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[idx:count] - f.ids = make([]pgid, len(ids)) - copy(f.ids, ids) - - // Make sure they're sorted. - sort.Sort(pgids(f.ids)) - } - - // Rebuild the page cache. - f.reindex() -} - -// write writes the page ids onto a freelist page. All free and pending ids are -// saved to disk since in the event of a program crash, all pending ids will -// become free. -func (f *freelist) write(p *page) error { - // Combine the old free pgids and pgids waiting on an open transaction. - - // Update the header flag. - p.flags |= freelistPageFlag - - // The page.count can only hold up to 64k elements so if we overflow that - // number then we handle it by putting the size in the first element. - lenids := f.count() - if lenids == 0 { - p.count = uint16(lenids) - } else if lenids < 0xFFFF { - p.count = uint16(lenids) - f.copyall(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[:]) - } else { - p.count = 0xFFFF - ((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[0] = pgid(lenids) - f.copyall(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[1:]) - } - - return nil -} - -// reload reads the freelist from a page and filters out pending items. -func (f *freelist) reload(p *page) { - f.read(p) - - // Build a cache of only pending pages. - pcache := make(map[pgid]bool) - for _, pendingIDs := range f.pending { - for _, pendingID := range pendingIDs { - pcache[pendingID] = true - } - } - - // Check each page in the freelist and build a new available freelist - // with any pages not in the pending lists. - var a []pgid - for _, id := range f.ids { - if !pcache[id] { - a = append(a, id) - } - } - f.ids = a - - // Once the available list is rebuilt then rebuild the free cache so that - // it includes the available and pending free pages. - f.reindex() -} - -// reindex rebuilds the free cache based on available and pending free lists. -func (f *freelist) reindex() { - f.cache = make(map[pgid]bool, len(f.ids)) - for _, id := range f.ids { - f.cache[id] = true - } - for _, pendingIDs := range f.pending { - for _, pendingID := range pendingIDs { - f.cache[pendingID] = true - } - } -} |