研究僵局–第3部分

在本系列的前兩個博客（第1部分和第2部分）中，我演示了如何創建一段死鎖的不良代碼，然后使用該代碼展示了進行線程轉儲的三種方式。在這個博客中，我將分析線程轉儲以找出錯誤的原因。

下面的討論同時涉及本系列第1部分中的Account和DeadlockDemo類，其中包含完整的代碼清單。

我需要做的第一件事是從DeadlockDemo應用程序中進行線程轉儲，就像他們過去在Blue Peter上所說的那樣：“這是我之前準備的”。

2012-10-16 13:37:03
Full thread dump Java HotSpot(TM) 64-Bit Server VM (20.10-b01-428 mixed mode):"DestroyJavaVM" prio=5 tid=7f9712001000 nid=0x110247000 waiting on condition [00000000]
java.lang.Thread.State: RUNNABLE"Thread-21" prio=5 tid=7f9712944000 nid=0x118d76000 waiting for monitor entry [118d75000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366f58> (a threads.deadlock.Account)
- locked <7f3366ee0> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-20" prio=5 tid=7f971216c000 nid=0x118c73000 waiting for monitor entry [118c72000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366e98> (a threads.deadlock.Account)
- locked <7f3366f58> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-19" prio=5 tid=7f9712943800 nid=0x118b70000 waiting for monitor entry [118b6f000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:81)
- waiting to lock <7f3366f40> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-18" prio=5 tid=7f9712942800 nid=0x118a6d000 waiting for monitor entry [118a6c000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:81)
- waiting to lock <7f3366f40> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-17" prio=5 tid=7f9712942000 nid=0x11896a000 waiting for monitor entry [118969000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:81)
- waiting to lock <7f3366ec8> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-16" prio=5 tid=7f9712941000 nid=0x118867000 waiting for monitor entry [118866000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:81)
- waiting to lock <7f3366ec8> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-15" prio=5 tid=7f9712940800 nid=0x118764000 waiting for monitor entry [118763000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:81)
- waiting to lock <7f3366ef8> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-14" prio=5 tid=7f971293f800 nid=0x118661000 waiting for monitor entry [118660000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:81)
- waiting to lock <7f3366f28> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-13" prio=5 tid=7f97129ae000 nid=0x11855e000 waiting for monitor entry [11855d000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:81)
- waiting to lock <7f3366eb0> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-12" prio=5 tid=7f97129ad000 nid=0x11845b000 waiting for monitor entry [11845a000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:81)
- waiting to lock <7f3366f40> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-11" prio=5 tid=7f97129ac800 nid=0x118358000 waiting for monitor entry [118357000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366f58> (a threads.deadlock.Account)
- locked <7f3366eb0> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-10" prio=5 tid=7f97129ab800 nid=0x118255000 waiting for monitor entry [118254000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:81)
- waiting to lock <7f3366eb0> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-9" prio=5 tid=7f97129ab000 nid=0x118152000 waiting for monitor entry [118151000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366e98> (a threads.deadlock.Account)
- locked <7f3366ec8> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-8" prio=5 tid=7f97129aa000 nid=0x11804f000 waiting for monitor entry [11804e000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366eb0> (a threads.deadlock.Account)
- locked <7f3366f28> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-7" prio=5 tid=7f97129a9800 nid=0x117f4c000 waiting for monitor entry [117f4b000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366eb0> (a threads.deadlock.Account)
- locked <7f3366e80> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-6" prio=5 tid=7f97129a8800 nid=0x117e49000 waiting for monitor entry [117e48000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:81)
- waiting to lock <7f3366e80> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-5" prio=5 tid=7f97128a1800 nid=0x117d46000 waiting for monitor entry [117d45000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:81)
- waiting to lock <7f3366f28> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-4" prio=5 tid=7f97121af800 nid=0x117c43000 waiting for monitor entry [117c42000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366e80> (a threads.deadlock.Account)
- locked <7f3366e98> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-3" prio=5 tid=7f97121ae800 nid=0x117b40000 waiting for monitor entry [117b3f000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366e80> (a threads.deadlock.Account)
- locked <7f3366ef8> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"Thread-2" prio=5 tid=7f971224a000 nid=0x117a3d000 waiting for monitor entry [117a3c000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366eb0> (a threads.deadlock.Account)
- locked <7f3366f40> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)"RMI TCP Accept-0" daemon prio=5 tid=7f97128fd800 nid=0x117837000 runnable [117836000]
java.lang.Thread.State: RUNNABLE
at java.net.PlainSocketImpl.socketAccept(Native Method)
at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:408)
- locked <7f32ee740> (a java.net.SocksSocketImpl)
at java.net.ServerSocket.implAccept(ServerSocket.java:462)
at java.net.ServerSocket.accept(ServerSocket.java:430)
at sun.management.jmxremote.LocalRMIServerSocketFactory$1.accept(LocalRMIServerSocketFactory.java:34)
at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(TCPTransport.java:369)
at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(TCPTransport.java:341)
at java.lang.Thread.run(Thread.java:680)"Poller SunPKCS11-Darwin" daemon prio=1 tid=7f97128fd000 nid=0x117734000 waiting on condition [117733000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at sun.security.pkcs11.SunPKCS11$TokenPoller.run(SunPKCS11.java:692)
at java.lang.Thread.run(Thread.java:680)"Low Memory Detector" daemon prio=5 tid=7f971209e000 nid=0x1173ec000 runnable [00000000]
java.lang.Thread.State: RUNNABLE"C2 CompilerThread1" daemon prio=9 tid=7f971209d000 nid=0x1172e9000 waiting on condition [00000000]
java.lang.Thread.State: RUNNABLE"C2 CompilerThread0" daemon prio=9 tid=7f971209c800 nid=0x1171e6000 waiting on condition [00000000]
java.lang.Thread.State: RUNNABLE"Signal Dispatcher" daemon prio=9 tid=7f971209b800 nid=0x1170e3000 waiting on condition [00000000]
java.lang.Thread.State: RUNNABLE"Surrogate Locker Thread (Concurrent GC)" daemon prio=5 tid=7f971209a800 nid=0x116fe0000 waiting on condition [00000000]
java.lang.Thread.State: RUNNABLE"Finalizer" daemon prio=8 tid=7f971209a000 nid=0x116d1c000 in Object.wait() [116d1b000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <7f3001300> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:118)
- locked <7f3001300> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:134)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159)"Reference Handler" daemon prio=10 tid=7f9712099000 nid=0x116c19000 in Object.wait() [116c18000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <7f30011d8> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:485)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116)
- locked <7f30011d8> (a java.lang.ref.Reference$Lock)"VM Thread" prio=9 tid=7f9712096800 nid=0x116b16000 runnable"Gang worker#0 (Parallel GC Threads)" prio=9 tid=7f9712002800 nid=0x1135c7000 runnable"Gang worker#1 (Parallel GC Threads)" prio=9 tid=7f9712003000 nid=0x1136ca000 runnable"Concurrent Mark-Sweep GC Thread" prio=9 tid=7f971204d800 nid=0x116790000 runnable
"VM Periodic Task Thread" prio=10 tid=7f97122d4000 nid=0x11793a000 waiting on condition"Exception Catcher Thread" prio=10 tid=7f9712001800 nid=0x1103ef000 runnable
JNI global references: 1037Found one Java-level deadlock:
=============================
"Thread-21":
waiting to lock monitor 7f97118bd560 (object 7f3366f58, a threads.deadlock.Account),
which is held by "Thread-20"
"Thread-20":
waiting to lock monitor 7f97118bc108 (object 7f3366e98, a threads.deadlock.Account),
which is held by "Thread-4"
"Thread-4":
waiting to lock monitor 7f9711834360 (object 7f3366e80, a threads.deadlock.Account),
which is held by "Thread-7"
"Thread-7":
waiting to lock monitor 7f97118b9708 (object 7f3366eb0, a threads.deadlock.Account),
which is held by "Thread-11"
"Thread-11":
waiting to lock monitor 7f97118bd560 (object 7f3366f58, a threads.deadlock.Account),
which is held by "Thread-20"Java stack information for the threads listed above:
===================================================
"Thread-21":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366f58> (a threads.deadlock.Account)
- locked <7f3366ee0> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-20":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366e98> (a threads.deadlock.Account)
- locked <7f3366f58> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-4":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366e80> (a threads.deadlock.Account)
- locked <7f3366e98> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-7":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366eb0> (a threads.deadlock.Account)
- locked <7f3366e80> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-11":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366f58> (a threads.deadlock.Account)
- locked <7f3366eb0> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)Found 1 deadlock.Heap
par new generation total 19136K, used 11590K [7f3000000, 7f44c0000, 7f44c0000)
eden space 17024K, 68% used [7f3000000, 7f3b51ac0, 7f40a0000)
from space 2112K, 0% used [7f40a0000, 7f40a0000, 7f42b0000)
to space 2112K, 0% used [7f42b0000, 7f42b0000, 7f44c0000)
concurrent mark-sweep generation total 63872K, used 0K [7f44c0000, 7f8320000, 7fae00000)
concurrent-mark-sweep perm gen total 21248K, used 8268K [7fae00000, 7fc2c0000, 800000000)

快速瀏覽，您可以看到此線程轉儲分為四個部分。這些是：

所有應用程序線程的完整列表
死鎖線程列表
一小堆死鎖線程
應用程序的堆摘要

線程列表

上面第一點中的線程列表是所有應用程序線程及其當前狀態的列表。從中您可以看到應用程序由一堆線程組成，您可以將它們大致分為兩部分。首先，有后臺線程。這些是每個應用程序所擁有的，而這些作為我們作為應用程序程序員通常不需要擔心的骯臟工作。它們具有諸如“ DestroyJavaVM ”， Low Memory Detector, Finalizer, Exception Catcher Thread and Concurrent Mark-Sweep GC Thread DestroyJavaVM Low Memory Detector, Finalizer, Exception Catcher Thread and Concurrent Mark-Sweep GC Thread 。其次，您或我可能會在我們的代碼中創建一些線程。這些名稱通常包含由單詞Thread和數字組成的名稱。例如： Thread-3, Thread-6 and Thread-20.

"Thread-20" prio=5 tid=7f971216c000 nid=0x118c73000 waiting for monitor entry [118c72000]
java.lang.Thread.State: BLOCKED (on object monitor)
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:82)
- waiting to lock <7f3366e98> (a threads.deadlock.Account)
- locked <7f3366f58> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:58)

詳細查看Thread-20上提供的信息，您會發現它可以分為幾部分。這些是：

<td>線程20 <td>如上所述的線程名稱。<tr> <td> prio = 5 <td>線程的優先級。從1到10的數字，其中1是最低優先級，10是最高優先級。 <tr> <tr> <td> tid = 7f971216c000 <td>線程ID。 Thread.getId（）調用返回的唯一數字。 <tr> <td> nid = 0x118c73000 <td>本機線程ID。這映射到平臺相關的線程ID。 <tr> <td>等待監視器輸入[118c72000]

java.lang.Thread.State：阻塞（在對象監視器上）<td>這是線程的狀態；在這種情況下，它已被阻止。還包括堆棧跟蹤概述了線程被阻塞的位置。

請注意，線程也可以標記為守護程序。例如：
“ RMI TCP Accept-0”守護進程prio = 5 tid = 7f97128fd800 nid = 0x117837000可運行[117836000] java.lang.Thread.State：可運行
守護程序線程是后臺任務線程，例如上面列出的RMI TCP Accept-0線程。守護程序線程是不會阻止JVM退出的線程。僅保留守護程序線程時，JVM將退出或關閉。

但是，線程列表并不能真正幫助您找到死鎖的原因，因此請快速前進...

死鎖線程列表

線程轉儲的此部分包含死鎖中涉及的所有線程的列表。

Found one Java-level deadlock:
=============================
"Thread-21":
waiting to lock monitor 7f97118bd560 (object 7f3366f58, a threads.deadlock.Account),
which is held by "Thread-20"
"Thread-20":
waiting to lock monitor 7f97118bc108 (object 7f3366e98, a threads.deadlock.Account),
which is held by "Thread-4"
"Thread-4":
waiting to lock monitor 7f9711834360 (object 7f3366e80, a threads.deadlock.Account),
which is held by "Thread-7"
"Thread-7":
waiting to lock monitor 7f97118b9708 (object 7f3366eb0, a threads.deadlock.Account),
which is held by "Thread-11"
"Thread-11":
waiting to lock monitor 7f97118bd560 (object 7f3366f58, a threads.deadlock.Account),
which is held by "Thread-20"

從上面的片段中，您可以看到有五個線程全部阻塞實例threads.deadlock.Account類

撇開監視器ID和帳戶實例，您可以看到“線程21”正在等待“線程20”，它正在等待“線程4”，而后者又正在等待“線程7”。 “線程7”正在等待“線程11”，這正在等待“線程20”：死鎖循環，如下圖所示：

死鎖堆棧痕跡

難題的最后一部分是死鎖線程堆棧跟蹤的列表，如下所示：

Java stack information for the threads listed above:
===================================================
"Thread-21":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366f58> (a threads.deadlock.Account)
- locked <7f3366ee0> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-20":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366e98> (a threads.deadlock.Account)
- locked <7f3366f58> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-4":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366e80> (a threads.deadlock.Account)
- locked <7f3366e98> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-7":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366eb0> (a threads.deadlock.Account)
- locked <7f3366e80> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-11":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366f58> (a threads.deadlock.Account)
- locked <7f3366eb0> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)

從上一節中，我們知道Thread-20正在通過a回路徑等待Thread-11而Thread-11正在等待Thread-20 。這是我們的僵局。

下一步是使用上面的線程堆棧跟蹤將此死鎖與代碼行聯系起來，我在下圖中對此進行了簡化。

在上圖中，為清楚起見，我從對象ID中刪除了7f3366前綴；因此，對象7f3366f58現在是f58 。從這個圖中，可以看到該對象f58被鎖定Thread-20上線59，并正在等待鎖對象e98上線86.箭頭下來，你可以看到， Thread-7正在等待鎖eb0上線86，而這又是通過鎖定Thread-11在線路59 Thread-11正在等待鎖f58上線86，其，循環備份，對線58通過鎖定Thread-20 。

那么，這些代碼行在哪里？下面顯示了第59行：

…這是第86行：

有時每個人都會感到驚訝，上面的堆棧軌跡使我感到驚訝。我期望鎖位于85和86行。但是，它們分別在59和86上。由于第59行不包含synced關鍵字，因此我猜測編譯器已經對transfer（…）方法的第一個synced關鍵字進行了一些優化。

由此可以得出的結論是，從列表中隨機選擇兩個Account對象的代碼將它們以錯誤的順序鎖定在第59行和第86行。那么，解決方法是什么？下次更多。但是，還有最后一點需要注意，即每次在程序上生成線程轉儲時，死鎖的組成可能都不相同。再次運行DeadlockDemo程序并使用kill -3 PID來獲取另一個線程轉儲后，我獲得了以下結果：

Found one Java-level deadlock:
=============================
"Thread-20":
waiting to lock monitor 7fdc7c802508 (object 7f311a530, a threads.deadlock.Account),
which is held by "Thread-3"
"Thread-3":
waiting to lock monitor 7fdc7a83d008 (object 7f311a518, a threads.deadlock.Account),
which is held by "Thread-11"
"Thread-11":
waiting to lock monitor 7fdc7c802508 (object 7f311a530, a threads.deadlock.Account),
which is held by "Thread-3"Java stack information for the threads listed above:
===================================================
"Thread-20":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f311a530> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-3":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:87)
- waiting to lock <7f311a518> (a threads.deadlock.Account)
- locked <7f311a530> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-11":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:87)
- waiting to lock <7f311a530> (a threads.deadlock.Account)
- locked <7f311a518> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)Found 1 deadlock.

在此線程轉儲中，死鎖中涉及的線程數量較少，但是如果您對其進行分析，則可以得出與我的第一個示例相同的結論。

下次：修改代碼…

有關更多信息，請參閱本系列中的其他博客。

該系列以及其他博客的所有源代碼都可以在Github上找到，網址為git：//github.com/roghughe/captaindebug.git

參考： 調查死鎖-第3部分： Captain Debug博客博客中來自JCG合作伙伴 Roger Hughes 的線程轉儲分析。