made HttpClientConnection reusable and stateless

Author: chernser

clickhouse-http-client/src/main/java11/com/clickhouse/client/http/HttpClientConnectionImpl.java

@@ -81,7 +81,6 @@ public List<Proxy> select(URI uri) {
 
     private static final String USER_AGENT = ClickHouseClientOption.buildUserAgent(null, "HttpClient");
 
-    private final AtomicBoolean busy;
     private final HttpClient httpClient;
     private final HttpRequest pingRequest;
 
@@ -197,15 +196,13 @@ protected HttpClientConnectionImpl(ClickHouseNode server, ClickHouseRequest<?> r
             builder.sslContext(ClickHouseSslContextProvider.getProvider().getSslContext(SSLContext.class, config)
                     .orElse(null));
         }
-
-        busy = new AtomicBoolean(false);
         httpClient = builder.build();
         pingRequest = newRequest(getBaseUrl() + "ping");
     }
 
     @Override
     protected boolean isReusable() {
-        return !busy.get();
+        return true; // httpClient is stateless and can be reused
     }
 
     private CompletableFuture<HttpResponse<InputStream>> postRequest(HttpRequest request) {
@@ -243,8 +240,6 @@ private ClickHouseHttpResponse postStream(ClickHouseConfig config, HttpRequest.B
             }
 
             return buildResponse(config, r, output, postAction);
-        } finally {
-            busy.set(false);
         }
     }
 
@@ -267,8 +262,6 @@ private ClickHouseHttpResponse postString(ClickHouseConfig config, HttpRequest.B
                 }
             }
             return buildResponse(config, r, output, postAction);
-        } finally {
-            busy.set(false);
         }
     }
 
@@ -281,9 +274,7 @@ protected final String getDefaultUserAgent() {
     protected ClickHouseHttpResponse post(ClickHouseConfig config, String sql, ClickHouseInputStream data,
             List<ClickHouseExternalTable> tables, ClickHouseOutputStream output, String url,
             Map<String, String> headers, Runnable postAction) throws IOException {
-        if (!busy.compareAndSet(false, true)) {
-            throw new ConnectException("Connection is busy");
-        }
+
         ClickHouseConfig c = config == null ? this.config : config;
         HttpRequest.Builder reqBuilder = HttpRequest.newBuilder()
                 .uri(URI.create(ClickHouseChecker.isNullOrEmpty(url) ? this.url : url))