Git.open(new File(localPath)) 报错

先说结论：最大支持5个对象同时处理Git git = Git.open(new File(localPath)); 的逻辑。提交的代码可以参考这里: fixed threadpool up to 5 threads with LinkedBlockingQueue of unlimited queue size

JGit工具可以使用类型如下代码创建Git git = Git.open(new File(localPath));

实际使用中遇到多个项目并行更新时报错，详情如下——

java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.CompletableFuture$AsyncSupply@46cc6ff9 rejected from java.util.concurrent.ThreadPoolExecutor@5c820ea8[Running, pool size = 5, active threads = 5, queued tasks = 0, completed tasks = 0]
        at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2063) ~[?:1.8.0_231]
        at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:830) ~[?:1.8.0_231]
        at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1379) ~[?:1.8.0_231]
        at java.util.concurrent.CompletableFuture.asyncSupplyStage(CompletableFuture.java:1604) ~[?:1.8.0_231]
        at java.util.concurrent.CompletableFuture.supplyAsync(CompletableFuture.java:1830) ~[?:1.8.0_231]
        at org.eclipse.jgit.util.FS$FileStoreAttributes.getFileStoreAttributes(FS.java:329) ~[org.eclipse.jgit-5.7.0.202003090808-r.jar:5.7.0.202003090808-r]
        at org.eclipse.jgit.util.FS$FileStoreAttributes.get(FS.java:296) ~[org.eclipse.jgit-5.7.0.202003090808-r.jar:5.7.0.202003090808-r]
        at org.eclipse.jgit.util.FS.getFileStoreAttributes(FS.java:767) ~[org.eclipse.jgit-5.7.0.202003090808-r.jar:5.7.0.202003090808-r]
        at org.eclipse.jgit.internal.storage.file.FileSnapshot.<init>(FileSnapshot.java:224) ~[org.eclipse.jgit-5.7.0.202003090808-r.jar:5.7.0.202003090808-r]
        at org.eclipse.jgit.internal.storage.file.FileSnapshot.<init>(FileSnapshot.java:205) ~[org.eclipse.jgit-5.7.0.202003090808-r.jar:5.7.0.202003090808-r]
        at org.eclipse.jgit.internal.storage.file.FileSnapshot.save(FileSnapshot.java:102) ~[org.eclipse.jgit-5.7.0.202003090808-r.jar:5.7.0.202003090808-r]
        at org.eclipse.jgit.internal.storage.file.FileRepository.<init>(FileRepository.java:209) ~[org.eclipse.jgit-5.7.0.202003090808-r.jar:5.7.0.202003090808-r]
        at org.eclipse.jgit.lib.BaseRepositoryBuilder.build(BaseRepositoryBuilder.java:583) ~[org.eclipse.jgit-5.7.0.202003090808-r.jar:5.7.0.202003090808-r]
        at org.eclipse.jgit.api.Git.open(Git.java:91) ~[org.eclipse.jgit-5.7.0.202003090808-r.jar:5.7.0.202003090808-r]
        at org.eclipse.jgit.api.Git.open(Git.java:71) ~[org.eclipse.jgit-5.7.0.202003090808-r.jar:5.7.0.202003090808-r]
        at com.stf.web.service.GitService.openGitPull(GitService.java:124) [sharestf.20200916162334.jar:?]

按图索骥即可，在BaseRepositoryBuilder的build方法中会新建R repo = (R) new FileRepository(setup());在FileRepository的构造方法中会进入FileSnapshot.save(getIndexFile());的逻辑——对于已存在的git仓库来说，代码——

if (!isBare()) {
            snapshot = FileSnapshot.save(getIndexFile());
        }

最终在读取FileStoreAttributes的方法getFileStoreAttributes(Path dir)中有异步调用——只有默认定义的Executor FUTURE_RUNNER进行执行操作。这个执行器的配置如下——

private static final Executor FUTURE_RUNNER = new ThreadPoolExecutor(0,
    5, 30L, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(),
    runnable -> {
        Thread t = new Thread(runnable, "FileStoreAttributeReader-" //$NON-NLS-1$
                + threadNumber.getAndIncrement());
        // Make sure these threads don't prevent application/JVM
        // shutdown.
        t.setDaemon(true);
        return t;
    });

这也是报错的原因：线程池中只有5个线程，都已经被占有Running, pool size = 5, active threads = 5, queued tasks = 0, completed tasks = 0

JGit中对Git的抽象需要研究下，为什么这里需要做一个FileSnapshot.save的动作？FileStore和FileStoreAttributes都代表什么含义？