为了创建一个新的、唯一的文件名,我使用以下代码:
File file = new File(name);
synchronized (sync) {
int cnt = 0;
while (file.exists()) {
file = new File(name + " (" + (cnt++) + ")");
}
file.createNewFile();
}
接下来,我使用该文件并将其删除。
当我在多线程情况下执行此操作时,有时会出现异常file.createNewFile()
:
java.io.IOException: Access is denied
at java.io.WinNTFileSystem.createFileExclusively(Native Method)
at java.io.File.createNewFile(File.java:1012)
以下代码重现了该问题(大多数情况下):
final int runs = 1000;
final int threads = 5;
final String name = "c:\\temp\\files\\file";
final byte[] bytes = getSomeBytes();
final Object sync = new Object();
ExecutorService exec = Executors.newFixedThreadPool(threads);
for (int thread = 0; thread < threads; thread++) {
final String id = "Runnable " + thread;
exec.execute(new Runnable() {
public void run() {
for (int i = 0; i < runs; i++) {
try {
File file = new File(name);
synchronized (sync) {
int cnt = 0;
while (file.exists()) {
file = new File(name + " (" + (cnt++) + ")");
}
file.createNewFile();
}
Files.write(file.toPath(), bytes);
file.delete();
} catch (Exception ex) {
System.err.println(id + ": exception after " + i
+ " runs: " + ex.getMessage());
ex.printStackTrace();
return;
}
}
System.out.println(id + " finished fine");
}
});
}
exec.shutdown();
while (!exec.awaitTermination(1, TimeUnit.SECONDS));
方法getSomeBytes()
只是生成一定数量的字节,实际内容并不重要:
byte[] getSomeBytes() throws UnsupportedEncodingException,
IOException {
byte[] alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWYZ1234567890\r\n"
.getBytes("UTF-8");
try (ByteArrayOutputStream baos = new ByteArrayOutputStream()) {
for (int i = 0; i < 100000; i++) {
baos.write(alphabet);
}
baos.flush();
return baos.toByteArray();
}
}
当我执行这段代码时,它有时会顺利进行,但大多数时候,它会生成一些异常,例如下面的输出:
Runnable 1: exception after 235 runs: Access is denied
java.io.IOException: Access is denied
at java.io.WinNTFileSystem.createFileExclusively(Native Method)
at java.io.File.createNewFile(File.java:1012)
at test.CreateFilesTest$1.run(CreateFilesTest.java:36)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Runnable 4: exception after 316 runs: Access is denied
java.io.IOException: Access is denied
at java.io.WinNTFileSystem.createFileExclusively(Native Method)
at java.io.File.createNewFile(File.java:1012)
at test.CreateFilesTest$1.run(CreateFilesTest.java:36)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Runnable 2: exception after 327 runs: Access is denied
java.io.IOException: Access is denied
at java.io.WinNTFileSystem.createFileExclusively(Native Method)
at java.io.File.createNewFile(File.java:1012)
at test.CreateFilesTest$1.run(CreateFilesTest.java:36)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Runnable 3 finished fine
Runnable 0 finished fine
有任何想法吗?我已经在 Windows 8 机器上使用 java 1.7.0_45 和 1.8.0_31 进行了测试,结果相同。
不确定问题是否与问题相同这个问题 https://stackoverflow.com/questions/10516472/file-createnewfile-randomly-fails,但它可以是。在我看来,在同一进程中使用多个线程似乎是问题的一部分,但我不能确定这一点,但它的复制速度更快。