replace mutex with cell

src/testutils.rs

@@ -3,13 +3,13 @@
 //! Those tests should only test public API surface in general, with some exceptions as provided by
 //! this module.
 use crate::Reader;
-use std::sync::Mutex;
+use std::cell::Cell;
 
 pub use crate::utils::State;
 
 thread_local! {
     /// Buffer of all debugging output logged internally by html5gum.
-    pub static OUTPUT: Mutex<String> = Default::default();
+    pub static OUTPUT: Cell<String> = Default::default();
 }
 
 /// Simple debug logger for tests.
@@ -20,15 +20,17 @@ thread_local! {
 ///
 /// A noop version for non-test builds is implemented in src/lib.rs
 pub fn trace_log(msg: String) {
-    OUTPUT.with(|lock| {
-        let mut buf = lock.lock().unwrap();
+    OUTPUT.with(|cell| {
+        let mut buf = cell.take();
         buf.push_str(&msg);
         buf.push('\n');
 
         if buf.len() > 20 * 1024 * 1024 {
             buf.clear();
             buf.push_str("[truncated output]\n");
         }
+
+        cell.set(buf);
     });
 }
 

tests/html5lib_tokenizer.rs

@@ -358,10 +358,11 @@ fn main() {
             Err(e) => {
                 let mut msg = String::new();
 
-                OUTPUT.with(|lock| {
-                    let mut buf = lock.lock().unwrap();
+                OUTPUT.with(|cell| {
+                    let mut buf = cell.take();
                     msg.push_str(&buf);
                     buf.clear();
+                    cell.set(buf);
                 });
 
                 msg.push_str("\n");