java - 多个用户访问 RDF 文件进行读写

Question

我使用 RDF 文件来存储由不同用户添加的有关各种主题的在线资源的链接 (URL)。

我正在 Apache 服务器上使用 Jena API 读取和写入 RDF 文件。

我担心的是，多个用户将被允许同时登录系统，并可能同时与文件交互。

我想知道这是否会导致更新文件时出现任何问题，例如是否会以某种方式损坏文件。我可以在实时应用程序中继续执行此操作吗？还是会因为多个用户同时访问 RDF 文件进行读写而导致我的应用程序崩溃。

我非常感谢您的帮助。

谢谢

赛义德

 //updated code to understand answer.
 // Example of Locks for reading

File f = new File(fileName); 
InputStream in = new FileInputStream(f);

Model model = ModelFactory.createDefaultModel();                
model.read(in,null);
String queryString = "...";


model.enterCriticalSection(Lock.READ);  // use of lock
try {

     qe = QueryExecutionFactory.create(qry, model);
     rs = qe.execSelect();
     for ( ; rs.hasNext() ; )
     {
         //read literals
         //read literals
         out.println(....);
     }
     qe.close();

 } finally 
   {
     model.leaveCriticalSection() ;
   }

//******************************
// Example of Locks for WRITING


File fout = new File(fileName); 
Model model = ModelFactory.createDefaultModel();                
model.read(in,null);
OutputStream os = new FileOutputStream(fout);
// model updation
// new triplets. new data being added

model.enterCriticalSection(Lock.WRITE);  // use of lock
try {
             model.write(os);
    } finally 
   {
     model.leaveCriticalSection() ;
   }

os.close();

Answer 1

看看 Concurrency HowTo耶拿网站。请点击 TDB/SDB 交易的相关链接。根据文档:

Locks provide critical section support for managing the interactions of multiple threads in the same JVM. Jena provides multiple-reader/single-writer concurrency support (MRSW).

The pattern general is:

Model model = . . . ;
model.enterCriticalSection(Lock.READ) ;  // or Lock.WRITE
try {
    ... perform actions on the model ...
    ... obey contract - no update operations if a read lock
} finally {
    model.leaveCriticalSection() ;
}