Options need to be added to the standard launch of a virtual machine (VM) to enable the debugging architecture, allowing us to attach (hook in) and collect data.
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-Xdebug |
Enables remote debugging. |
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-Xnoagent |
On a Sun VM, disables the proprietary debugging interface thus letting JPDA work correctly.在Sun VM上，禁用專有除錯介面，從而允許JPDA正確工作。 |
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-Djava.compiler=NONE |
Disables Just-In-Time (JIT) compilation.. 我們一般debug程式的時候，只是關注其中的一部分程式碼，而且大部分情況下是設定斷點，然後單步執行，而JIT的編譯單位是class，只要我們執行了class裡面的程式碼，JIT就會對整個class進行編譯，而我們實際執行的程式碼一般都是其中的一部分程式碼，所以從整個時間效率上來看，採用JIT反而更費時間。也就是說在JVM遠端除錯這個事情上，禁用JIT（只使用轉譯器，解釋一行執行一條）更合理，所以通過-Djava.compiler=NONE來禁止JIT。 |
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-Xrunjdwp: transport=dt_socket, server=y, address=5000, suspend=y |
Loads JDWP (Java Debug Wire Protocol), the reference implementation of JPDA. Sub-options further specify the option. |
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transport=dt_socket |
Sets the transport type for the connection with the debugging application; in this example, we will connect via a socket. |
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server=y |
Tells the VM whether it must be receptive to an attaching debugging application. |
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address=5000 |
The port address for our connection; we will need 5000 for our example. |
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suspend=y |
This option can be set depending on whether we want to suspend the exectution of the VM until a debugging application connects. This is useful if we seek to understand what happens when a server starts. |
1、If we wish to make the VM wait for a connection before a full launch, we will need a command line such as this :
java …. -Xdebug -Xnoagent -Djava.compiler=NONE -Xrunjdwp:transport=dt_socket,server=y,address=5000,suspend=y
2、If we want the VM to be fully executing and listening for a debugging application, we will require a command line such as this one :
java …. -Xdebug -Xnoagent -Djava.compiler=NONE -Xrunjdwp:transport=dt_socket,server=y,address=5000,suspend=n
第2種模式是一種比較好的方式，VM採用偵聽的方式等待除錯程式的連線。