From 927e5d327209901cca56de0bccacf6d2b33e055a Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@sbcglobal.net>
Date: Fri, 18 Sep 2015 17:47:06 -0400
Subject: dl: Keep track of if a handle has been closed

---
 dl/dlfcn.go | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/dl/dlfcn.go b/dl/dlfcn.go
index 3ab5abb..db8bd63 100644
--- a/dl/dlfcn.go
+++ b/dl/dlfcn.go
@@ -24,6 +24,7 @@ package dl
 
 import (
 	"errors"
+	"sync"
 	"unsafe"
 )
 
@@ -32,6 +33,8 @@ import (
 //#include <dlfcn.h>
 import "C"
 
+var HandleClosedError = errors.New("Handle is already closed")
+
 type Flag int
 
 // POSIX specifies these four flags to Open().
@@ -54,6 +57,8 @@ const (
 
 type Handle struct {
 	c unsafe.Pointer
+	o int
+	l sync.RWMutex
 }
 
 // Open a shared object file, returning a Handle to it, or an error.
@@ -73,7 +78,7 @@ func Open(name string, flags Flag) (Handle, error) {
 	if ptr == nil {
 		return Handle{}, dlerror()
 	}
-	return Handle{ptr}, nil
+	return Handle{c: ptr, o: 1}, nil
 }
 
 // Look up a symbol, and return a pointer to it.
@@ -82,6 +87,13 @@ func Open(name string, flags Flag) (Handle, error) {
 // dl cannot obtain unsafe.Pointers without importing the unsafe
 // package explicitly.
 func (h Handle) Sym(symbol string) (uintptr, error) {
+	h.l.RLock()
+	defer h.l.RUnlock()
+
+	if h.o == 0 {
+		return 0, HandleClosedError
+	}
+
 	symbolC := C.CString(symbol)
 	defer C.free(unsafe.Pointer(symbolC))
 
@@ -97,11 +109,21 @@ func (h Handle) Sym(symbol string) (uintptr, error) {
 // count; if the reference count drops below 0, then the object is
 // unloaded.
 func (h Handle) Close() error {
+	h.l.Lock()
+	defer h.l.Unlock()
+
+	if h.o == 0 {
+		return HandleClosedError
+	}
+
 	dlerror()
 	r := C.dlclose(h.c)
 	if r != 0 {
 		return dlerror()
 	}
+	if h.o == 1 {
+		h.o = 0
+	}
 	return nil
 }
 
-- 
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