package bbolt import ( "fmt" "sort" "unsafe" ) // txPending holds a list of pgids and corresponding allocation txns // that are pending to be freed. type txPending struct { ids []pgid alloctx []txid // txids allocating the ids lastReleaseBegin txid // beginning txid of last matching releaseRange } // pidSet holds the set of starting pgids which have the same span size type pidSet map[pgid]struct{} // 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 { freelistType FreelistType // freelist type ids []pgid // all free and available free page ids. allocs map[pgid]txid // mapping of txid that allocated a pgid. pending map[txid]*txPending // mapping of soon-to-be free page ids by tx. cache map[pgid]bool // fast lookup of all free and pending page ids. freemaps map[uint64]pidSet // key is the size of continuous pages(span), value is a set which contains the starting pgids of same size forwardMap map[pgid]uint64 // key is start pgid, value is its span size backwardMap map[pgid]uint64 // key is end pgid, value is its span size allocate func(txid txid, n int) pgid // the freelist allocate func free_count func() int // the function which gives you free page number mergeSpans func(ids pgids) // the mergeSpan func getFreePageIDs func() []pgid // get free pgids func readIDs func(pgids []pgid) // readIDs func reads list of pages and init the freelist } // newFreelist returns an empty, initialized freelist. func newFreelist(freelistType FreelistType) *freelist { f := &freelist{ freelistType: freelistType, allocs: make(map[pgid]txid), pending: make(map[txid]*txPending), cache: make(map[pgid]bool), freemaps: make(map[uint64]pidSet), forwardMap: make(map[pgid]uint64), backwardMap: make(map[pgid]uint64), } if freelistType == FreelistMapType { f.allocate = f.hashmapAllocate f.free_count = f.hashmapFreeCount f.mergeSpans = f.hashmapMergeSpans f.getFreePageIDs = f.hashmapGetFreePageIDs f.readIDs = f.hashmapReadIDs } else { f.allocate = f.arrayAllocate f.free_count = f.arrayFreeCount f.mergeSpans = f.arrayMergeSpans f.getFreePageIDs = f.arrayGetFreePageIDs f.readIDs = f.arrayReadIDs } return f } // 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() } // arrayFreeCount returns count of free pages(array version) func (f *freelist) arrayFreeCount() int { return len(f.ids) } // pending_count returns count of pending pages func (f *freelist) pending_count() int { var count int for _, txp := range f.pending { count += len(txp.ids) } 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 _, txp := range f.pending { m = append(m, txp.ids...) } sort.Sort(m) mergepgids(dst, f.getFreePageIDs(), m) } // arrayAllocate 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) arrayAllocate(txid txid, 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) } f.allocs[initial] = txid 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. txp := f.pending[txid] if txp == nil { txp = &txPending{} f.pending[txid] = txp } allocTxid, ok := f.allocs[p.id] if ok { delete(f.allocs, p.id) } else if (p.flags & freelistPageFlag) != 0 { // Freelist is always allocated by prior tx. allocTxid = txid - 1 } 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. txp.ids = append(txp.ids, id) txp.alloctx = append(txp.alloctx, allocTxid) f.cache[id] = true } } // 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, txp := 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, txp.ids...) delete(f.pending, tid) } } f.mergeSpans(m) } // releaseRange moves pending pages allocated within an extent [begin,end] to the free list. func (f *freelist) releaseRange(begin, end txid) { if begin > end { return } var m pgids for tid, txp := range f.pending { if tid < begin || tid > end { continue } // Don't recompute freed pages if ranges haven't updated. if txp.lastReleaseBegin == begin { continue } for i := 0; i < len(txp.ids); i++ { if atx := txp.alloctx[i]; atx < begin || atx > end { continue } m = append(m, txp.ids[i]) txp.ids[i] = txp.ids[len(txp.ids)-1] txp.ids = txp.ids[:len(txp.ids)-1] txp.alloctx[i] = txp.alloctx[len(txp.alloctx)-1] txp.alloctx = txp.alloctx[:len(txp.alloctx)-1] i-- } txp.lastReleaseBegin = begin if len(txp.ids) == 0 { delete(f.pending, tid) } } f.mergeSpans(m) } // rollback removes the pages from a given pending tx. func (f *freelist) rollback(txid txid) { // Remove page ids from cache. txp := f.pending[txid] if txp == nil { return } var m pgids for i, pgid := range txp.ids { delete(f.cache, pgid) tx := txp.alloctx[i] if tx == 0 { continue } if tx != txid { // Pending free aborted; restore page back to alloc list. f.allocs[pgid] = tx } else { // Freed page was allocated by this txn; OK to throw away. m = append(m, pgid) } } // Remove pages from pending list and mark as free if allocated by txid. delete(f.pending, txid) f.mergeSpans(m) } // 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 (p.flags & freelistPageFlag) == 0 { panic(fmt.Sprintf("invalid freelist page: %d, page type is %s", p.id, p.typ())) } // 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 : idx+count] // copy the ids, so we don't modify on the freelist page directly idsCopy := make([]pgid, count) copy(idsCopy, ids) // Make sure they're sorted. sort.Sort(pgids(idsCopy)) f.readIDs(idsCopy) } } // arrayReadIDs initializes the freelist from a given list of ids. func (f *freelist) arrayReadIDs(ids []pgid) { f.ids = ids f.reindex() } func (f *freelist) arrayGetFreePageIDs() []pgid { return f.ids } // 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 _, txp := range f.pending { for _, pendingID := range txp.ids { 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.getFreePageIDs() { if !pcache[id] { a = append(a, id) } } f.readIDs(a) } // reindex rebuilds the free cache based on available and pending free lists. func (f *freelist) reindex() { ids := f.getFreePageIDs() f.cache = make(map[pgid]bool, len(ids)) for _, id := range ids { f.cache[id] = true } for _, txp := range f.pending { for _, pendingID := range txp.ids { f.cache[pendingID] = true } } } // arrayMergeSpans try to merge list of pages(represented by pgids) with existing spans but using array func (f *freelist) arrayMergeSpans(ids pgids) { sort.Sort(ids) f.ids = pgids(f.ids).merge(ids) }