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本文主要研究下JEP 102: Process API Updates

PRocessHandle

/Library/Java/JavaVirtualMachines/jdk-9.0.4.jdk/Contents/Home/lib/src.zip!/java.base/java/lang/ProcessHandle.java

java9新引入了ProcessHandle

/**  * ProcessHandle identifies and provides control of native processes. Each  * individual process can be monitored for liveness, list its children,  * get information about the process or destroy it.  * By comparison, {@link java.lang.Process Process} instances were started  * by the current process and additionally provide access to the process  * input, output, and error streams.  * <p>  * The native process ID is an identification number that the  * operating system assigns to the process.  * The range for process id values is dependent on the operating system.  * For example, an embedded system might use a 16-bit value.  * Status information about a process is retrieved from the native system  * and may change asynchronously; processes may be created or terminate  * spontaneously.  * The time between when a process terminates and the process id  * is reused for a new process is unpredictable.  * Race conditions can exist between checking the status of a process and  * acting upon it. When using ProcessHandles avoid assumptions  * about the liveness or identity of the underlying process.  * <p>  * Each ProcessHandle identifies and allows control of a process in the native  * system. ProcessHandles are returned from the factory methods {@link #current()},  * {@link #of(long)},  * {@link #children}, {@link #descendants}, {@link #parent()} and  * {@link #allProcesses()}.  * <p>  * The {@link Process} instances created by {@link ProcessBuilder} can be queried  * for a ProcessHandle that provides information about the Process.  * ProcessHandle references should not be freely distributed.  *  * <p>  * A {@link java.util.concurrent.CompletableFuture} available from {@link #onExit}  * can be used to wait for process termination, and possibly trigger dependent  * actions.  * <p>  * The factory methods limit access to ProcessHandles using the  * SecurityManager checking the {@link RuntimePermission RuntimePermission("manageProcess")}.  * The ability to control processes is also restricted by the native system,  * ProcessHandle provides no more access to, or control over, the native process  * than would be allowed by a native application.  *  * @implSpec  * In the case where ProcessHandles cannot be supported then the factory  * methods must consistently throw {@link java.lang.UnsupportedOperationException}.  * The methods of this class throw {@link java.lang.UnsupportedOperationException}  * if the operating system does not allow access to query or kill a process.  *  * <p>  * The {@code ProcessHandle} static factory methods return instances that are  * <a href="{@docRoot}/java/lang/doc-files/ValueBased.htML">value-based</a>,  * immutable and thread-safe.  * Use of identity-sensitive operations (including reference equality  * ({@code ==}), identity hash code, or synchronization) on these instances of  * {@code ProcessHandle} may have unpredictable results and should be avoided.  * Use {@link #equals(Object) equals} or  * {@link #compareTo(ProcessHandle) compareTo} methods to compare ProcessHandles.  *  * @see Process  * @since 9  */ public interface ProcessHandle extends Comparable<ProcessHandle> { //... }

ProcessHandle提供了对本地进程的控制，可以监控其存活，查找其子进程，查看其信息，甚至销毁它。非常适合耗时较长的进程调用。

实例

查看进程信息

    @test     public void testProcessHandle() {         final ProcessHandle processHandle = ProcessHandle.current();         final ProcessHandle.Info info = processHandle.info();         System.out.println("Process info =>");         System.out.format("PID: %s%n", processHandle.pid());         info.arguments().ifPresent(args -> System.out.format("Arguments: %s%n", Arrays.toString(args)));         info.command().ifPresent(command -> System.out.format("Command: %s%n", command));         info.commandLine()                 .ifPresent(commandLine -> System.out.format("Command line: %s%n", commandLine));         info.startInstant()                 .ifPresent(startInstant -> System.out.format("Start time: %s%n", startInstant));         info.totalCpuDuration()                 .ifPresent(cpuDuration -> System.out.format("CPU time: %s%n", cpuDuration));         info.user().ifPresent(user -> System.out.format("User: %s%n", user));     }

启动/销毁进程

    @Test     public void testControlProcess() throws IOException {         final ProcessBuilder processBuilder = new ProcessBuilder("top")                 .inheritIO();         ProcessHandle processHandle = processBuilder.start().toHandle();         final CountDownLatch latch = new CountDownLatch(1);          processHandle.onExit().when@R_304_639@Async((handle, throwable) -> {             if (throwable == null) {                 System.out.println(handle.pid());             } else {                 throwable.printStackTrace();             }             latch.countDown();         });         final Thread shutdownThread = new Thread(() -> {             try {                 Thread.sleep(1000);             } catch (final InterruptedException e) {                 e.printStackTrace();             }             if (processHandle.supportsNormalTermination()) {                 processHandle.destroy();             } else {                 processHandle.destroyForcibly();             }         });         shutdownThread.start();         try {             shutdownThread.join();             latch.await();         } catch (final InterruptedException e) {             e.printStackTrace();         }     }

小结

java9对process api的最大的更新就是引进了ProcessHandle，可以用来查看进程信息，监控并销毁它。

doc

• Java 9 新特性概述
• exploring-java-9 feature9/process
• java9系列(一)安装及jshell使用
• java9系列(二)docker运行java9
• java9系列(三)模块系统精要