runtime/logger: use blocking wait.

Fixes #84 using the first solution.

If the performance is considered too slow,
we can do the second option later.

src/runtime/src/logger.rs

@@ -38,7 +38,8 @@ impl<'a> Drop for LogBufferRef<'a> {
 
 pub struct BufferLogger {
     buffer:      Mutex<LogBuffer<&'static mut [u8]>>,
-    uart_filter: Cell<LevelFilter>
+    uart_filter: Cell<LevelFilter>,
+    buffer_filter: Cell<LevelFilter>,
 }
 
 static mut LOGGER: Option<BufferLogger> = None;
@@ -48,6 +49,7 @@ impl BufferLogger {
         BufferLogger {
             buffer: Mutex::new(LogBuffer::new(buffer)),
             uart_filter: Cell::new(LevelFilter::Info),
+            buffer_filter: Cell::new(LevelFilter::Trace),
         }
     }
 
@@ -76,6 +78,15 @@ impl BufferLogger {
     pub fn set_uart_log_level(&self, max_level: LevelFilter) {
         self.uart_filter.set(max_level)
     }
+
+    pub fn buffer_log_level(&self) -> LevelFilter {
+        self.buffer_filter.get()
+    }
+
+    /// this should be reserverd for mgmt module
+    pub fn set_buffer_log_level(&self, max_level: LevelFilter) {
+        self.buffer_filter.set(max_level)
+    }
 }
 
 // required for impl Log
@@ -94,7 +105,8 @@ impl Log for BufferLogger {
             let seconds   = timestamp / 1_000_000;
             let micros    = timestamp % 1_000_000;
 
-            if let Some(mut buffer) = self.buffer.try_lock() {
+            if record.level() <= self.buffer_log_level() {
+                let mut buffer = self.buffer.lock();
                 writeln!(buffer, "[{:6}.{:06}s] {:>5}({}): {}", seconds, micros,
                          record.level(), record.target(), record.args()).unwrap();
             }

src/runtime/src/mgmt.rs

@@ -98,9 +98,9 @@ async fn handle_connection(stream: &mut TcpStream, pull_id: Rc<RefCell<u32>>) ->
         let msg: Request = FromPrimitive::from_i8(msg?).ok_or(Error::UnrecognizedPacket)?;
         match msg {
             Request::GetLog => {
-                let mut buffer = get_logger_buffer().await;
+                let buffer = get_logger_buffer().await.extract().as_bytes().to_vec();
                 write_i8(stream, Reply::LogContent as i8).await?;
-                write_chunk(stream, buffer.extract().as_bytes()).await?;
+                write_chunk(stream, &buffer).await?;
             }
             Request::ClearLog => {
                 let mut buffer = get_logger_buffer().await;
@@ -115,24 +115,22 @@ async fn handle_connection(stream: &mut TcpStream, pull_id: Rc<RefCell<u32>>) ->
                 };
                 loop {
                     let mut buffer = get_logger_buffer_pred(|b| !b.is_empty()).await;
-                    let bytes = buffer.extract().as_bytes();
                     if id != *pull_id.borrow() {
                         // another connection attempts to pull the log...
                         // abort this connection...
                         break;
                     }
-                    write_chunk(stream, bytes).await?;
+                    let bytes = buffer.extract().as_bytes().to_vec();
+                    buffer.clear();
+                    core::mem::drop(buffer);
+                    write_chunk(stream, &bytes).await?;
                     if log::max_level() == LevelFilter::Trace {
-                        // Hold exclusive access over the logger until we get positive
-                        // acknowledgement; otherwise we get an infinite loop of network
-                        // trace messages being transmitted and causing more network
-                        // trace messages to be emitted.
-                        //
-                        // Any messages unrelated to this management socket that arrive
-                        // while it is flushed are lost, but such is life.
+                        // temporarily discard all trace level log
+                        let logger = unsafe { BufferLogger::get_logger().as_mut().unwrap() };
+                        logger.set_buffer_log_level(LevelFilter::Debug);
                         stream.flush().await?;
+                        logger.set_buffer_log_level(LevelFilter::Trace);
                     }
-                    buffer.clear();
                 }
             },
             Request::SetLogFilter => {