Add thread pool support for BGI CBG Decoder

src/ext/mutex.rs

@@ -0,0 +1,19 @@
+//! Extension for [std::sync::Mutex].
+pub trait MutexExt<T> {
+    /// Lock the mutex, blocking the current thread until it can be acquired.
+    fn lock_blocking(&self) -> std::sync::MutexGuard<'_, T>;
+}
+
+impl<T> MutexExt<T> for std::sync::Mutex<T> {
+    fn lock_blocking(&self) -> std::sync::MutexGuard<'_, T> {
+        loop {
+            match self.try_lock() {
+                Ok(guard) => return guard,
+                Err(std::sync::TryLockError::WouldBlock) => {
+                    std::thread::yield_now();
+                }
+                Err(std::sync::TryLockError::Poisoned(err)) => return err.into_inner(),
+            }
+        }
+    }
+}