Make lock and unlock &self.

Fixes #74

src/lib.rs

@@ -646,15 +646,15 @@ impl Mmap {
     ///
     /// See [mlock()](https://man7.org/linux/man-pages/man2/mlock.2.html) map page.
     #[cfg(unix)]
-    pub fn lock(&mut self) -> Result<()> {
+    pub fn lock(&self) -> Result<()> {
         self.inner.lock()
     }
 
     /// Unlock the whole memory map. Only supported on Unix.
     ///
     /// See [munlock()](https://man7.org/linux/man-pages/man2/munlock.2.html) map page.
     #[cfg(unix)]
-    pub fn unlock(&mut self) -> Result<()> {
+    pub fn unlock(&self) -> Result<()> {
         self.inner.unlock()
     }
 }
@@ -837,15 +837,15 @@ impl MmapRaw {
     ///
     /// See [mlock()](https://man7.org/linux/man-pages/man2/mlock.2.html) map page.
     #[cfg(unix)]
-    pub fn lock(&mut self) -> Result<()> {
+    pub fn lock(&self) -> Result<()> {
         self.inner.lock()
     }
 
     /// Unlock the whole memory map. Only supported on Unix.
     ///
     /// See [munlock()](https://man7.org/linux/man-pages/man2/munlock.2.html) map page.
     #[cfg(unix)]
-    pub fn unlock(&mut self) -> Result<()> {
+    pub fn unlock(&self) -> Result<()> {
         self.inner.unlock()
     }
 }
@@ -1105,15 +1105,15 @@ impl MmapMut {
     ///
     /// See [mlock()](https://man7.org/linux/man-pages/man2/mlock.2.html) map page.
     #[cfg(unix)]
-    pub fn lock(&mut self) -> Result<()> {
+    pub fn lock(&self) -> Result<()> {
         self.inner.lock()
     }
 
     /// Unlock the whole memory map. Only supported on Unix.
     ///
     /// See [munlock()](https://man7.org/linux/man-pages/man2/munlock.2.html) map page.
     #[cfg(unix)]
-    pub fn unlock(&mut self) -> Result<()> {
+    pub fn unlock(&self) -> Result<()> {
         self.inner.unlock()
     }
 }
@@ -1728,7 +1728,7 @@ mod test {
             .unwrap();
         file.set_len(128).unwrap();
 
-        let mut mmap = unsafe { Mmap::map(&file).unwrap() };
+        let mmap = unsafe { Mmap::map(&file).unwrap() };
         #[cfg(target_os = "linux")]
         assert!(!is_locked());