Automate memory management for Pigosat instances

README.md

@@ -46,10 +46,11 @@ Use
 ---
 
 After completing the building and installation steps above, importation should
-work as usual. Create a `Pigosat` object `p` and use its methods. Because of the
-C-language PicoSAT component of PiGoSAT, you must explicitly free `p` when you
-are done using `p`, and you will not be able to use `p` thereafter. The best
-practice if you are using `p` all within one function is to use `defer`.
+work as usual. Create a `Pigosat` object `p` and use its methods. Even though
+PicoSAT is written in C, PiGoSAT manages memory for you using
+`runtime.SetFinalizer`. (If you reset a `Pigosat` instance `p`'s finalizer, you
+will have to call `p.Delete` explicitly, which is best done with `defer` right
+after reseting the finalizer; most users will not need to worry about this.)
 
 Designing your model is beyond the scope of this document, but Googling
 "satisfiability problem", "conjunctive normal form", and "DIMACS" are good
@@ -65,7 +66,6 @@ package main
 import "pigosat"
 func main() {
 	p := pigosat.NewPigosat(0)
-	defer p.Delete()
 	p.AddClauses([][]int32{{1, 2}, {-2}})
 	status, solution := p.Solve()
 	// Now status should equal pigosat.Satisfiable and solution should be

pigosat.go

@@ -10,6 +10,7 @@ package pigosat
 // #include "picosat.h"
 import "C"
 import "fmt"
+import "runtime"
 import "sync"
 import "time"
 
@@ -53,12 +54,16 @@ func NewPigosat(propagation_limit uint64) *Pigosat {
 	if propagation_limit > 0 {
 		C.picosat_set_propagation_limit(p, C.ulonglong(propagation_limit))
 	}
-	return &Pigosat{p: p, lock: new(sync.RWMutex)}
+	pgo := &Pigosat{p: p, lock: new(sync.RWMutex)}
+	runtime.SetFinalizer(pgo, (*Pigosat).Delete)
+	return pgo
 }
 
-// DelPigosat must be called on every Pigosat instance before each goes out of
-// scope or the program ends, or else the program will leak memory. Once
-// DelPigosat has been called on an instance, it cannot be used again.
+// Delete may be called when you are done using a Pigosat instance, after which
+// it cannot be used again. However, you only need to call this method if the
+// instance's finalizer was reset using runtime.SetFinalizer (if you're not
+// sure, it's always safe to call Delete again). Most users will not need this
+// method.
 func (p *Pigosat) Delete() {
 	if p == nil || p.p == nil {
 		return

pigosat_test.go

@@ -139,7 +139,6 @@ func TestFormulas(t *testing.T) {
 		p.AddClauses(ft.formula)
 		status, solution = p.Solve()
 		wasExpected(t, i, p, &ft, status, solution)
-		p.Delete()
 	}
 }
 
@@ -159,11 +158,9 @@ func TestPropLimit(t *testing.T) {
 				t.Errorf("Propagation limit %d had no effect on formula 0",
 					limit)
 			}
-			p.Delete()
 			continue
 		}
 		wasExpected(t, 0, p, &ft, status, solution)
-		p.Delete()
 	}
 }
 
@@ -202,7 +199,6 @@ func TestPicosatVersion(t *testing.T) {
 // This is the example from the README.
 func Example_readme() {
 	p := NewPigosat(0)
-	defer p.Delete()
 	p.AddClauses([][]int32{{1, 2}, {-2}})
 	fmt.Println("")
 	fmt.Printf("# variables == %d\n", p.Variables())