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1   /*
2    * Copyright 2014 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   https://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package io.netty.channel.epoll;
17  
18  import io.netty.channel.ChannelOption;
19  import io.netty.channel.unix.FileDescriptor;
20  import io.netty.util.internal.SystemPropertyUtil;
21  
22  /**
23   * Tells if <a href="https://netty.io/wiki/native-transports.html">{@code netty-transport-native-epoll}</a> is
24   * supported.
25   */
26  public final class Epoll {
27  
28      private static final Throwable UNAVAILABILITY_CAUSE;
29  
30      static {
31          Throwable cause = null;
32  
33          if (SystemPropertyUtil.getBoolean("io.netty.transport.noNative", false)) {
34              cause = new UnsupportedOperationException(
35                      "Native transport was explicit disabled with -Dio.netty.transport.noNative=true");
36          } else {
37              FileDescriptor epollFd = null;
38              FileDescriptor eventFd = null;
39              try {
40                  epollFd = Native.newEpollCreate();
41                  eventFd = Native.newEventFd();
42              } catch (Throwable t) {
43                  cause = t;
44              } finally {
45                  if (epollFd != null) {
46                      try {
47                          epollFd.close();
48                      } catch (Exception ignore) {
49                          // ignore
50                      }
51                  }
52                  if (eventFd != null) {
53                      try {
54                          eventFd.close();
55                      } catch (Exception ignore) {
56                          // ignore
57                      }
58                  }
59              }
60          }
61  
62          UNAVAILABILITY_CAUSE = cause;
63      }
64  
65      /**
66       * Returns {@code true} if and only if the <a href="https://netty.io/wiki/native-transports.html">{@code
67       * netty-transport-native-epoll}</a> is available.
68       */
69      public static boolean isAvailable() {
70          return UNAVAILABILITY_CAUSE == null;
71      }
72  
73      /**
74       * Ensure that <a href="https://netty.io/wiki/native-transports.html">{@code netty-transport-native-epoll}</a> is
75       * available.
76       *
77       * @throws UnsatisfiedLinkError if unavailable
78       */
79      public static void ensureAvailability() {
80          if (UNAVAILABILITY_CAUSE != null) {
81              throw (Error) new UnsatisfiedLinkError(
82                      "failed to load the required native library").initCause(UNAVAILABILITY_CAUSE);
83          }
84      }
85  
86      /**
87       * Returns the cause of unavailability of <a href="https://netty.io/wiki/native-transports.html">
88       * {@code netty-transport-native-epoll}</a>.
89       *
90       * @return the cause if unavailable. {@code null} if available.
91       */
92      public static Throwable unavailabilityCause() {
93          return UNAVAILABILITY_CAUSE;
94      }
95  
96      /**
97       * Returns {@code true} if the epoll native transport is both {@linkplain #isAvailable() available} and supports
98       * {@linkplain ChannelOption#TCP_FASTOPEN_CONNECT client-side TCP FastOpen}.
99       *
100      * @return {@code true} if it's possible to use client-side TCP FastOpen via epoll, otherwise {@code false}.
101      */
102     public static boolean isTcpFastOpenClientSideAvailable() {
103         return isAvailable() && Native.IS_SUPPORTING_TCP_FASTOPEN_CLIENT;
104     }
105 
106     /**
107      * Returns {@code true} if the epoll native transport is both {@linkplain #isAvailable() available} and supports
108      * {@linkplain ChannelOption#TCP_FASTOPEN server-side TCP FastOpen}.
109      *
110      * @return {@code true} if it's possible to use server-side TCP FastOpen via epoll, otherwise {@code false}.
111      */
112     public static boolean isTcpFastOpenServerSideAvailable() {
113         return isAvailable() && Native.IS_SUPPORTING_TCP_FASTOPEN_SERVER;
114     }
115 
116     private Epoll() {
117     }
118 }