libmimalloc-sys: expose mit_usable_size

Author: Andronik Ordian

libmimalloc-sys/src/lib.rs

@@ -10,6 +10,7 @@ extern "C" {
     pub fn mi_malloc_aligned(size: usize, alignment: usize) -> *const c_void;
     pub fn mi_realloc_aligned(p: *const c_void, size: usize, alignment: usize) -> *const c_void;
     pub fn mi_free(p: *const c_void) -> c_void;
+    pub fn mi_usable_size(p: *mut c_void) -> usize;
 }
 
 #[cfg(test)]
@@ -34,4 +35,14 @@ mod tests {
         let ptr = unsafe { mi_realloc_aligned(ptr as *const c_void, 8, 8) } as *mut u8;
         unsafe { mi_free(ptr as *const c_void) };
     }
+
+    #[test]
+    fn it_calculates_usable_size() {
+        let ptr = unsafe { mi_malloc(32) } as *mut u8;
+        let usable_size = unsafe { mi_usable_size(ptr as *mut c_void) };
+        assert!(
+            usable_size >= 32,
+            "usable_size should at least equal to the allocated size"
+        );
+    }
 }