pgraph, resources: Major refactor to remove pgraph to resource dep

This is the mechanical port of the remaining bits. Next to clean it up a
bit.

resources/semaphore.go

@@ -0,0 +1,125 @@
+// Mgmt
+// Copyright (C) 2013-2017+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package resources
+
+import (
+	"fmt"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+
+	"github.com/purpleidea/mgmt/pgraph"
+	"github.com/purpleidea/mgmt/util/semaphore"
+
+	multierr "github.com/hashicorp/go-multierror"
+)
+
+// SemaSep is the trailing separator to split the semaphore id from the size.
+const SemaSep = ":"
+
+// SemaLock acquires the list of semaphores in the graph.
+func SemaLock(g *pgraph.Graph, semas []string) error {
+	var reterr error
+	sort.Strings(semas) // very important to avoid deadlock in the dag!
+	slock := SemaLockFromGraph(g)
+	smap := SemaMapFromGraph(g) // returns a map, which can be modified by ref
+
+	for _, id := range semas {
+		slock.Lock()         // semaphore creation lock
+		sema, ok := smap[id] // lookup
+		if !ok {
+			size := SemaSize(id) // defaults to 1
+			smap[id] = semaphore.NewSemaphore(size)
+			sema = smap[id]
+		}
+		slock.Unlock()
+
+		if err := sema.P(1); err != nil { // lock!
+			reterr = multierr.Append(reterr, err) // list of errors
+		}
+	}
+	return reterr
+}
+
+// SemaUnlock releases the list of semaphores in the graph.
+func SemaUnlock(g *pgraph.Graph, semas []string) error {
+	var reterr error
+	sort.Strings(semas) // unlock in the same order to remove partial locks
+	smap := SemaMapFromGraph(g)
+
+	for _, id := range semas {
+		sema, ok := smap[id] // lookup
+		if !ok {
+			// programming error!
+			panic(fmt.Sprintf("graph: sema: %s does not exist", id))
+		}
+
+		if err := sema.V(1); err != nil { // unlock!
+			reterr = multierr.Append(reterr, err) // list of errors
+		}
+	}
+	return reterr
+}
+
+// SemaSize returns the size integer associated with the semaphore id. It
+// defaults to 1 if not found.
+func SemaSize(id string) int {
+	size := 1 // default semaphore size
+	// valid id's include "some_id", "hello:42" and ":13"
+	if index := strings.LastIndex(id, SemaSep); index > -1 && (len(id)-index+len(SemaSep)) >= 1 {
+		// NOTE: we only allow size > 0 here!
+		if i, err := strconv.Atoi(id[index+len(SemaSep):]); err == nil && i > 0 {
+			size = i
+		}
+	}
+	return size
+}
+
+// SemaLockFromGraph returns a pointer to the semaphore lock stored with the
+// graph, otherwise it panics. If one does not exist, it will create it.
+func SemaLockFromGraph(g *pgraph.Graph) *sync.Mutex {
+	x, exists := g.Value("slock")
+	if !exists {
+		g.SetValue("slock", &sync.Mutex{})
+		x, _ = g.Value("slock")
+	}
+
+	slock, ok := x.(*sync.Mutex)
+	if !ok {
+		panic("not a *sync.Mutex")
+	}
+	return slock
+}
+
+// SemaMapFromGraph returns a pointer to the map of semaphores stored with the
+// graph, otherwise it panics. If one does not exist, it will create it.
+func SemaMapFromGraph(g *pgraph.Graph) map[string]*semaphore.Semaphore {
+	x, exists := g.Value("semas")
+	if !exists {
+		semas := make(map[string]*semaphore.Semaphore)
+		g.SetValue("semas", semas)
+		x, _ = g.Value("semas")
+	}
+
+	semas, ok := x.(map[string]*semaphore.Semaphore)
+	if !ok {
+		panic("not a map[string]*semaphore.Semaphore")
+	}
+	return semas
+}