java - 如何修复 'This operation can be a deadlock cause'

Question

当我第二次调用 sendDM() 时，我收到死锁警告。我该如何解决这个问题？

我正在使用 JDA Api，并且正在尝试获取我使用 RestAction .complete() 发送的消息

    private void start(){

        sendDM(getP1().getUser());
        sendDM(getP2().getUser());

        EmbedBuilder embedBuilder = new EmbedBuilder();
        textChannel.sendMessage(p1.getUser().getAsMention() + " " + p2.getUser().getAsMention()).queue();
        textChannel.sendMessage(embedBuilder.setTitle("**Match has started - #" + getGameId() + "**")
                        .addField("Info", "ID: " + getGameId() + "\nMap: 7189-0031-5500" + "\nStatus: " + getStatus().toString(),true)
                        .addField("Player 1", p1.getUser().getAsMention() + " - Host", false)
                        .addField("Player 2", p2.getUser().getAsMention(), false)
                        .addField("Lobby", textChannel.getAsMention(), false)
                        .setFooter("Both participants will receive a Private Message where they can submit match results", null).build())
                .queue();


    }

    private void sendDM(User user){

        EmbedBuilder embedBuilder = new EmbedBuilder();
        user.openPrivateChannel().queue((channel) ->
        {
            channel.sendMessage(p1.getUser().getAsMention() + " " + p2.getUser().getAsMention()).queue();
            Message message = channel.sendMessage(embedBuilder.setTitle("**Match has started - #" + getGameId() + "**")
                    .addField("Info", "ID: " + getGameId() + "\nMap: 7189-0031-5500" + "\nStatus: " + getStatus().toString(),true)
                    .addField("Player 1", p1.getUser().getAsMention() + " - Host", false)
                    .addField("Player 2", p2.getUser().getAsMention(), false)
                    .addField("Lobby", textChannel.getAsMention(), false)
                    .addField("**If you win**", ":white_check_mark:", true)
                    .addField("**If you loose**", ":x:", true)
                    .setFooter("Both participants will receive a Private Message where they can submit match results", null).build())
                    .complete();
            message.addReaction("\u274C").complete();
            message.addReaction("\u2705").complete();

        });

    }

我希望它只返回消息，但我收到此错误:

[ForkJoinPool.commonPool-worker-1] ERROR net.dv8tion.jda.api.requests.RestAction - Encountered error while processing success consumer
java.lang.IllegalStateException: Preventing use of complete() in callback threads! This operation can be a deadlock cause
    at net.dv8tion.jda.internal.requests.RestActionImpl.complete(RestActionImpl.java:187)
    at net.dv8tion.jda.api.requests.RestAction.complete(RestAction.java:357)
    at match.Match.lambda$sendDM$0(Match.java:71)
    at net.dv8tion.jda.api.requests.Request.lambda$onSuccess$0(Request.java:83)
    at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1402)
    at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
    at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
    at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
    at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)

Answer 1

只有一个回调线程用于运行回调。*

您的调用 user.openPrivateChannel().queue((channel) -> {...} 在此单个回调线程中运行。

您的调用 message.addReaction("\u274C").complete(); 会阻塞直到完成，但它将在同一个回调线程上运行，该线程已经忙于运行外部想要运行complete()的回调...你看到了问题。这是在幕后检测到的，并抛出异常以防止发生这种死锁。

只需使用 message.addReaction("\u274C").queue(); 即可。 queue() 立即返回，以便回调线程有机会在外部回调完成后运行它。

请参阅 complete() 的文档和 queue() .

<小时/>

*请参阅这些故障排除文档 here :

Since we decided to use a single-thread pool (1) we only have one thread to execute callbacks. This thread is used by the first callback (2) and cannot be used for the second callback (3).

Due to this reason we simply don't allow using complete() in any callback threads at all. If you use callbacks you should use queue().

(Copyright 2015-2019 Austin Keener, Michael Ritter, Florian Spieß)