Address comments

core/src/main/java/com/linecorp/armeria/client/AbstractHttpRequestHandler.java

@@ -169,7 +169,7 @@ final boolean tryInitialize() {
                         "Can't send requests. ID: " + id + ", session active: " +
                         session.isAcquirable(responseDecoder.keepAliveHandler()));
             }
-            session.deactivate();
+            session.markUnacquirable();
             // No need to send RST because we didn't send any packet and this will be disconnected anyway.
             fail(UnprocessedRequestException.of(exception));
             return false;
@@ -223,7 +223,7 @@ final void writeHeaders(RequestHeaders headers) {
             // connection by sending a GOAWAY frame that will be sent after receiving the corresponding
             // response from the remote peer. The "Connection: close" header is stripped when it is converted to
             // a Netty HTTP/2 header.
-            session.deactivate();
+            session.markUnacquirable();
         }
 
         final ChannelPromise promise = ch.newPromise();
@@ -329,9 +329,11 @@ private void fail(Throwable cause) {
     }
 
     final void failAndReset(Throwable cause) {
-        // Mark the session as unhealthy so that subsequent requests do not use it.
-        final HttpSession session = HttpSession.get(ch);
-        session.deactivate();
+        if (cause instanceof WriteTimeoutException) {
+            final HttpSession session = HttpSession.get(ch);
+            // Mark the session as unhealthy so that subsequent requests do not use it.
+            session.markUnacquirable();
+        }
 
         if (cause instanceof ProxyConnectException || cause instanceof ResponseCompleteException) {
             // - ProxyConnectException is handled by HttpSessionHandler.exceptionCaught().

core/src/main/java/com/linecorp/armeria/client/Http1ResponseDecoder.java

@@ -183,7 +183,7 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
                         }
 
                         if (!HttpUtil.isKeepAlive(nettyRes)) {
-                            session().deactivate();
+                            session().markUnacquirable();
                         }
 
                         final HttpResponseWrapper res = getResponse(resId);

core/src/main/java/com/linecorp/armeria/client/Http2ResponseDecoder.java

@@ -159,14 +159,14 @@ public void onStreamRemoved(Http2Stream stream) {}
 
     @Override
     public void onGoAwaySent(int lastStreamId, long errorCode, ByteBuf debugData) {
-        session().deactivate();
+        session().markUnacquirable();
         goAwayHandler.onGoAwaySent(channel(), lastStreamId, errorCode, debugData);
     }
 
     @Override
     public void onGoAwayReceived(int lastStreamId, long errorCode, ByteBuf debugData) {
         // Should not reuse a connection that received a GOAWAY frame.
-        session().deactivate();
+        session().markUnacquirable();
         goAwayHandler.onGoAwayReceived(channel(), lastStreamId, errorCode, debugData);
     }
 

core/src/main/java/com/linecorp/armeria/client/HttpClientPipelineConfigurator.java

@@ -805,7 +805,7 @@ private static final class ReadSuppressingAndChannelDeactivatingHandler extends
 
         @Override
         public void close(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
-            HttpSession.get(ctx.channel()).deactivate();
+            HttpSession.get(ctx.channel()).markUnacquirable();
             super.close(ctx, promise);
         }
     }

core/src/main/java/com/linecorp/armeria/client/HttpSessionHandler.java

@@ -327,7 +327,7 @@ public boolean isAcquirable(KeepAliveHandler keepAliveHandler) {
     }
 
     @Override
-    public void deactivate() {
+    public void markUnacquirable() {
         isAcquirable = false;
     }
 

core/src/main/java/com/linecorp/armeria/client/WebSocketHttp1ClientChannelHandler.java

@@ -180,7 +180,7 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
                     }
 
                     if (!HttpUtil.isKeepAlive(nettyRes)) {
-                        session().deactivate();
+                        session().markUnacquirable();
                     }
 
                     if (res == null && ArmeriaHttpUtil.isRequestTimeoutResponse(nettyRes)) {

core/src/main/java/com/linecorp/armeria/internal/client/DefaultClientRequestContext.java

@@ -1013,7 +1013,7 @@ public CompletableFuture<Void> initiateConnectionShutdown() {
                 });
                 // To deactivate the channel when initiateShutdown is called after the RequestHeaders is sent.
                 // The next request will trigger shutdown.
-                HttpSession.get(ch).deactivate();
+                HttpSession.get(ch).markUnacquirable();
             }
         });
         return completableFuture;

core/src/main/java/com/linecorp/armeria/internal/client/HttpSession.java

@@ -17,6 +17,7 @@
 package com.linecorp.armeria.internal.client;
 
 import com.linecorp.armeria.client.ClientRequestContext;
+import com.linecorp.armeria.client.WriteTimeoutException;
 import com.linecorp.armeria.common.ClosedSessionException;
 import com.linecorp.armeria.common.HttpRequest;
 import com.linecorp.armeria.common.SerializationFormat;
@@ -90,7 +91,7 @@ public boolean isAcquirable(KeepAliveHandler keepAliveHandler) {
         }
 
         @Override
-        public void deactivate() {}
+        public void markUnacquirable() {}
 
         @Override
         public int incrementAndGetNumRequestsSent() {
@@ -137,9 +138,10 @@ static HttpSession get(Channel ch) {
      *     <li>A connection is closed.</li>
      *     <li>"Connection: close" header is sent or received.</li>
      *     <li>A GOAWAY frame is sent or received.</li>
+     *     <li>A {@link WriteTimeoutException} is raised</li>
      * </ul>
      */
-    void deactivate();
+    void markUnacquirable();
 
     /**
      * Returns {@code true} if a new request can be sent with this {@link HttpSession}.