ensure hashmap init clears maps

This reorders some statements in the hashmap initialization to ensure we
always start fresh, even when no pageids were passed to it.

fixes #791

Signed-off-by: Thomas Jungblut <tjungblu@redhat.com>

Author: tjungblu

freelist_hmap.go

@@ -195,22 +195,22 @@ func (f *freelist) delSpan(start common.Pgid, size uint64) {
 // initial from pgids using when use hashmap version
 // pgids must be sorted
 func (f *freelist) init(pgids []common.Pgid) {
+	// reset the counter when freelist init
+	f.freePagesCount = 0
+	f.freemaps = make(map[uint64]pidSet)
+	f.forwardMap = make(map[common.Pgid]uint64)
+	f.backwardMap = make(map[common.Pgid]uint64)
+
 	if len(pgids) == 0 {
 		return
 	}
 
-	size := uint64(1)
-	start := pgids[0]
-	// reset the counter when freelist init
-	f.freePagesCount = 0
-
-	if !sort.SliceIsSorted([]common.Pgid(pgids), func(i, j int) bool { return pgids[i] < pgids[j] }) {
+	if !sort.SliceIsSorted(pgids, func(i, j int) bool { return pgids[i] < pgids[j] }) {
 		panic("pgids not sorted")
 	}
 
-	f.freemaps = make(map[uint64]pidSet)
-	f.forwardMap = make(map[common.Pgid]uint64)
-	f.backwardMap = make(map[common.Pgid]uint64)
+	size := uint64(1)
+	start := pgids[0]
 
 	for i := 1; i < len(pgids); i++ {
 		// continuous page

freelist_test.go

@@ -179,6 +179,32 @@ func TestFreelist_releaseRange(t *testing.T) {
 	}
 }
 
+func TestFreeList_reload_page_dedupe(t *testing.T) {
+	buf := make([]byte, 4096)
+	f := newTestFreelist()
+	f.readIDs([]common.Pgid{5, 6, 8})
+
+	p := common.LoadPage(buf)
+	if err := f.write(p); err != nil {
+		t.Fatal(err)
+	}
+
+	f2 := newTestFreelist()
+	f.readIDs([]common.Pgid{})
+
+	f2.free(common.Txid(5), common.NewPage(5, common.LeafPageFlag, 0, 4))
+
+	// reload should deduplicate as a pending page when reading from p's freelist
+	f2.reload(p)
+
+	if len(f2.getFreePageIDs()) != 0 {
+		t.Fatalf("expected empty; got=%v", f2.getFreePageIDs())
+	}
+	if exp := []common.Pgid{5, 6, 7, 8, 9}; !reflect.DeepEqual(exp, f2.pending[5].ids) {
+		t.Fatalf("exp=%v; got=%v", exp, f2.pending[5].ids)
+	}
+}
+
 func TestFreelistHashmap_allocate(t *testing.T) {
 	f := newTestFreelist()
 	if f.freelistType != FreelistMapType {