java.lang.IllegalMonitorStateException : object not locked by thread before wait() 异常

Question

但是我在“花名册”对象被更新的任何地方进行同步。怎么会？

违规代码:

 public Roster getRoster() {
    if (roster == null) {
        return null;
    }

    if (!roster.rosterInitialized) {
        try {
            synchronized (roster) {
                roster.reload();
                long waitTime = SmackConfiguration.getPacketReplyTimeout();
                long start = System.currentTimeMillis();
                while (!roster.rosterInitialized) {
                    if (waitTime <= 0) {
                        break;
                    }
                    roster.wait(waitTime);
                    long now = System.currentTimeMillis();
                    waitTime -= now - start;
                    start = now;
                }
            }
        }
        catch (InterruptedException ie) {
            // Ignore.
        }
    }
    return roster;
}

Answer 1

“gets new'ed”是指创建一个新名册对象？

您确定同步正确吗？同步发生在实例，而不是变量。所以如果你这样做，例如

synchronized(roster) {
  roster = new Roster();
  // do something
}

然后您只同步到旧，而不是新 花名册。

所以下面的代码应该会产生同样的错误:

Roster roster = new Roster();
Roster othervariable = roster;
synchronized(othervariable) {
  roster = new Roster(); // create a new roster
  othervariable.wait(1000); // OK, since synchronized with this instance!
  roster.wait(1000); // NOT OK, not synchronized with *new* roster!
}

同步不会发生在变量名称上，而是发生在内容上。如果覆盖内容，则不会重新同步到新值!