Corda技术理解之阅读源码的小知识和小问题记录

冷不防 2022-03-25 11:23 173阅读 0赞

#### 小知识 ####

##### process\_id在Corda启动中的意义。 #####

process\_id是Corda任何的节点启动的时候，都会默认生成这样一个文件的。

1.  **Corda中源码的描述如下**  
    // Write out our process ID (which may or may not resemble a UNIX process id - to us it’s just a string) to a  
    // file that we’ll do our best to delete on exit. But if we don’t, it’ll be overwritten next time. If it already  
    // exists, we try to take the file lock first before replacing it and if that fails it means we’re being started  
    // twice with the same directory: that’s a user error and we should bail out.
2.  **它为什么有这样一个文件？**  
    为了保证同一个路径下的节点，只能够启动一次，防止多次启动同一个节点。上述的描述更为具体。
3.  **它的实现过程？**  
    1，一开始的时候，Corda也不知道当前这个节点是否启动了。所以它仍然会生成属于自己的process\_id字符串（数字），生成文件。
    
    2，对此文件执行如下操作：  
    val pidFileLock = pidFileRw.channel.tryLock()
    
    3，如果无法对此文件进行上锁，则表明此节点已经在启动中了。目前还不知道为什么可以这样判断？
4.  **Corda源码实现逻辑过程**

val pidFile = (baseDirectory / "process-id").toFile()
    pidFile.createNewFile()
    val pidFileRw = RandomAccessFile(pidFile, "rw")
    val pidFileLock = pidFileRw.channel.tryLock()
    if (pidFileLock == null) {
       println("It appears there is already a node running with the specified data directory $baseDirectory")
       println("Shut that other node down and try again. It may have process ID ${pidFile.readText()}")
       System.exit(1)
    }
    pidFile.deleteOnExit()
    // Avoid the lock being garbage collected. We don't really need to release it as the OS will do so for us
    // when our process shuts down, but we try in stop() anyway just to be nice.
    addShutdownHook {
       pidFileLock.release()
    }
    val ourProcessID: String = ManagementFactory.getRuntimeMXBean().name.split("@")[0]
    pidFileRw.setLength(0)
    pidFileRw.write(ourProcessID.toByteArray())

对此文件调用了一个钩子。  
当退出的时候，需要删除此文件，并且释放锁。

--------------------

### 小问题 ###

1.  启动的时候：如果版本太低，有bug。如下：[bug描述过程][bug]
2.  Paths.get("").normalize() throws ArrayIndexOutOfBoundsException when using Oracle JDK 8u20.  
    Stack trace:  
    Exception in thread “main” java.lang.ArrayIndexOutOfBoundsException: 0  
    at sun.nio.fs.UnixPath.normalize(UnixPath.java:508)  
    at net.corda.node.services.config.ConfigHelper.loadConfig(ConfigUtilities.kt:34)  
    at net.corda.node.services.config.ConfigHelper.loadConfig$default(ConfigUtilities.kt:30)  
    at net.corda.node.MainKt.main(Main.kt:74)  
    Solution is to upgrade JDK above version 1.8.0\_20. Suggest we catch this exception and print the solution to screen -> Upgrade JDK above version 1.8.0\_20 or something.  
    So Corda defines a method named canNormalizeEmptyPath that can catch exception when node starts at Oracle JDK 8u20 and print the solution to screen.

--------------------

#### 小结 ####

1.  记录一个Corda节点启动时候，默认生成的一个process\_id文件的相关知识。
2.  记录一个bug。

[bug]: https://github.com/corda/corda/issues/83