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由JSP的预编译加速谈如何参与开源

科技 09-06 来源：知乎

原标题：由JSP的预编译加速谈如何参与开源软件工程师，公众号「Tomcat那些事儿」

很早之前的文章，写过一篇关于加速Web应用的功能之一：「JSP预编译」JSP预编译，加速你的应用,在其中我们提到通过JSP的预编译，我们可以提前生成JSP对应的Servlet文件，从而节省执行时再生成所带来的时间占用。JSPC

而整个JSP预编译的核心入口是 JspC这个工具。

下面两篇是预编译具体的工作原理：你了解Tomcat是怎样处理Jsp文件的吗?修改JSP文件实时生效的秘密

新的 Tomcat Release Note 里，有一个功能，是新增了多线程编译，来加速JSP预编译。是一位热心网友提供的 patch。

我们来看下具体内容： Make the Jasper (JSP Engine) Java file generation process multi-threaded. By default, one thread will be used per core. Based on a patch by Dan Fabulich.

这个 patch主要做了些什么事情呢？我把其中的重点代码摘出来一起看下：通过输入参数，设置线程数public void setThreadCount(String threadCount) { if (threadCount == null) { return; } int newThreadCount; try { if (threadCount.endsWith("C")) { double factor = Double.parseDouble(threadCount.substring(0, threadCount.length() - 1)); newThreadCount = (int) (factor * Runtime.getRuntime().availableProcessors()); } else { newThreadCount = Integer.parseInt(threadCount); } } catch (NumberFormatException e) { throw new BuildException("Couldn't parse thread count: " + threadCount); } if (newThreadCount < 1) { throw new BuildException("There must be at least one thread: " + newThreadCount); } this.threadCount = newThreadCount; }增加线程池的使用

上面根据输入配置好的threadCount，会在后面生成线程池的时候被使用到，同时生成的线程池，会做为提交JSP编译工作的入口。ExecutorService threadPool = Executors.newFixedThreadPool(threadCount);ExecutorCompletionService<Void> service = new ExecutorCompletionService<>(threadPool);int pageCount = pages.size(); for (String nextjsp : pages) { File fjsp = new File(nextjsp); if (!fjsp.isAbsolute()) { fjsp = new File(uriRootF, nextjsp); } if (!fjsp.exists()) { if (log.isWarnEnabled()) { log.warn(Localizer.getMessage( "jspc.error.fileDoesNotExist", fjsp.toString())); } continue; } String s = fjsp.getAbsolutePath(); if (s.startsWith(uriRoot)) { nextjsp = s.substring(uriRoot.length()); } if (nextjsp.startsWith("." + File.separatorChar)) { nextjsp = nextjsp.substring(2); } service.submit(new ProcessFile(nextjsp)); }patch的完整diffIndex: java/org/apache/jasper/JspC.java===================================================================--- java/org/apache/jasper/JspC.java (revision 1355850)+++ java/org/apache/jasper/JspC.java (working copy)@@ -43,6 +43,11 @@ import java.util.Stack; import java.util.StringTokenizer; import java.util.Vector;+import java.util.concurrent.Callable;+import java.util.concurrent.ExecutionException;+import java.util.concurrent.ExecutorCompletionService;+import java.util.concurrent.ExecutorService;+import java.util.concurrent.Executors; import javax.servlet.jsp.tagext.TagLibraryInfo; @@ -126,6 +131,7 @@ protected static final String SWITCH_ENCODING = "-javaEncoding"; protected static final String SWITCH_SMAP = "-smap"; protected static final String SWITCH_DUMP_SMAP = "-dumpsmap";+ protected static final String SWITCH_THREAD_COUNT = "-threadCount"; protected static final String SHOW_SUCCESS ="-s"; protected static final String LIST_ERRORS = "-l"; protected static final int INC_WEBXML = 10;@@ -209,6 +215,9 @@ * is UTF-8. Added per bugzilla 19622. */ protected String javaEncoding = "UTF-8";+ + /** The number of threads to use; default is two per core */+ protected int threadCount = 0; // Generation of web.xml fragments protected String webxmlFile;@@ -363,6 +372,8 @@ smapSuppressed = false; } else if (tok.equals(SWITCH_DUMP_SMAP)) { smapDumped = true;+ } else if (tok.equals(SWITCH_THREAD_COUNT)) {+ setThreadCount(nextArg()); } else { if (tok.startsWith("-")) { throw new JasperException("Unrecognized option: " + tok +@@ -720,6 +731,31 @@ return javaEncoding; } + public int getThreadCount() {+ return threadCount;+ }+ + public void setThreadCount(String threadCount) {+ if (threadCount == null) return;+ int newThreadCount;+ if (threadCount.endsWith("C")) {+ try {+ double factor = Double.parseDouble(threadCount.substring(0, threadCount.length() - 1));+ newThreadCount = (int) (factor * (double) Runtime.getRuntime().availableProcessors());+ } catch (NumberFormatException e) {+ throw new BuildException("Couldn't parse thread count: " + threadCount);+ }+ } else {+ try {+ newThreadCount = Integer.parseInt(threadCount);+ } catch (NumberFormatException e) {+ throw new BuildException("Couldn't parse thread count: " + threadCount);+ }+ }+ if (newThreadCount < 1) throw new BuildException("There must be at least one thread: " + newThreadCount);+ this.threadCount = newThreadCount;+ }+ /** * Sets the encoding to use for * java files.@@ -1305,28 +1341,51 @@ initWebXml(); Iterator<String> iter = pages.iterator();- while (iter.hasNext()) {- String nextjsp = iter.next().toString();- File fjsp = new File(nextjsp);- if (!fjsp.isAbsolute()) {- fjsp = new File(uriRootF, nextjsp);- }- if (!fjsp.exists()) {- if (log.isWarnEnabled()) {- log.warn- (Localizer.getMessage- ("jspc.error.fileDoesNotExist", fjsp.toString()));+ if (threadCount == 0) {+ threadCount = 2 * Runtime.getRuntime().availableProcessors();+ }+ ExecutorService threadPool = null;+ try {+ threadPool = Executors.newFixedThreadPool(threadCount);+ ExecutorCompletionService<Void> service = new ExecutorCompletionService<Void>(threadPool);+ int fileCount = 0;+ while (iter.hasNext()) {+ String nextjsp = iter.next().toString();+ File fjsp = new File(nextjsp);+ if (!fjsp.isAbsolute()) {+ fjsp = new File(uriRootF, nextjsp); }- continue;+ if (!fjsp.exists()) {+ if (log.isWarnEnabled()) {+ log.warn+ (Localizer.getMessage+ ("jspc.error.fileDoesNotExist", fjsp.toString()));+ }+ continue;+ }+ String s = fjsp.getAbsolutePath();+ if (s.startsWith(uriRoot)) {+ nextjsp = s.substring(uriRoot.length());+ }+ if (nextjsp.startsWith("." + File.separatorChar)) {+ nextjsp = nextjsp.substring(2);+ }+ service.submit(new ProcessFile(nextjsp));+ fileCount++; }- String s = fjsp.getAbsolutePath();- if (s.startsWith(uriRoot)) {- nextjsp = s.substring(uriRoot.length());+ for (int i = 0; i < fileCount; i++) {+ service.take().get(); }- if (nextjsp.startsWith("." + File.separatorChar)) {- nextjsp = nextjsp.substring(2);+ } catch (InterruptedException e) {+ throw new JasperException(e);+ } catch (ExecutionException e) {+ if (e.getCause() instanceof JasperException) {+ throw (JasperException) e.getCause();+ } else {+ throw new JasperException(e.getCause()); }- processFile(nextjsp);+ } finally {+ if (threadPool != null) threadPool.shutdownNow(); } completeWebXml();@@ -1354,6 +1413,18 @@ } } }+ + private class ProcessFile implements Callable<Void> {+ private final String file;+ private ProcessFile(String file) { this.file = file; }+ + @Override+ public Void call() throws Exception {+ processFile(file);+ return null;+ }+ + } // ==================== protected utility methods ==================== Index: java/org/apache/jasper/resources/LocalStrings.properties===================================================================--- java/org/apache/jasper/resources/LocalStrings.properties (revision 1355850)+++ java/org/apache/jasper/resources/LocalStrings.properties (working copy)@@ -184,6 +184,7 @@ \ -javaEncoding <enc> Set the encoding charset for Java classes (default UTF-8)\n\ \ -source <version> Set the -source argument to the compiler (default 1.6)\n\ \ -target <version> Set the -target argument to the compiler (default 1.6)\n\+\ -threadCount <count> Number of threads. \"2.0C\" means two threads per core\n\ jspc.webxml.header=<?xml version="1.0" encoding="ISO-8859-1"?>\n\ \n\怎样提 Patch

根据不同的开源项目，风格上不太一样。

像 Tomcat 这种较大型的项目，虽然也在 GitHub 上有代码，但主要风格还是前几年流行的 SVN + JIRA + Bugzilla。主要的Bug 和 Feature 的需求，都需要先在 JIRA 或者 Bugzilla上创建。对于提交的 path，做为附件内容，同步提供。之后大家围绕这个话题进行讨论，commiter 会决定是否采用合入。

其它在GitHub上托管的开源项目，直接提交Pull Request，然后邮件联系 commiter即可。对方会在 PR 后面进行讨论，决定是否采用，流程上也更清晰。一些感想

看上面的 patch 内容，我们可能感觉没啥难度，「不就是用个线程池？」可能现象确实如此，这个思路也比较容易想到。但在这其中的一些思路可以借鉴的，比如输入参数中，会默认设置一个core对应两个线程，我们一般的思路是根据 Runtime 直接取Processor数设置上就完事了。

另外一点是，我上面的历史文章中，有一篇分析文章是2015年写的，网上之前也有不少类似分析源码的文章，好像也都是「仅」分析，「这么容易想到的思路」，为什么没人在分析的时候提个patch? 所以，有些看似简单的地方也都是有可优化的点，甚至方法也不难，难在发现并下手。

说到这里顺便吐槽下 Tomcat，这个 patch 是热心网友在 2012提的，结果直到今年(2018.07)才采用合入，也真是够拖沓的。