XPCOM C++多线程和javascript回调

Question

背景

在12.0以下的XULRunner版本中,它可以工作,但是当我尝试将其移植到12.0或更高版本时,它会使应用程序崩溃.主要原因是在sdk v12或更新的开发人员中删除代理对象到xpcom组件并建议通过使用nsRunnable/nsIRunnable包装对象来替换它,并通过函数NS_DispatchToMainThread将调用路由到主线程(单击此处)

我正在开发什么？

我创建了db连接器,它通过回调与主线程异步和通信.使用:XULRunner v6,移植到XULRunner v17或更高版本

    //nsIDBCallback.idl
    [scriptable, function, uuid(XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX)]
    interface nsIDBCallback : nsISupports {
       void onInfo(in long phase, in long status, in string info);
    }

    //nsDBService.h, it is XPCOM component 
    class nsDBService : public nsIDBService, nsIRunnable
    {
    public:
       NS_DECL_ISUPPORTS
       NS_DECL_NSIRUNNABLE
       NS_DECL_NSIDBSERVICE

    private:
       std::vector<nsIThread*>     threads;
       std::vector<nsIDBCallback*> callbacks;
       std::vector<const char*>    sqls;

       nsIThread* makeNewThread();
       void       runOperationIfNotBussy();

    public:
       NS_IMETHODIMP Query(const char *sql, nsIDBCallback *callback);
    }

    //nsDBService.cpp
    // adding query and other data to buffers, 
    // it's thread safe, there are used mutex's
    NS_IMETHODIMP nsDBService::Query(const char *sql, nsIDBCallback *callback)
    {
       callbacks.push_back(callback);
       sqls     .push_back(sql);
       threads  .push_back( makeNewThread() );

       //run added operation if db driver is free, 
       //if driver is bussy then invocation is in buffer and need to wait
       runOperationIfNotBussy();

       return NS_OK;
    }

    void nsDBService::runOperationIfNotBussy() 
    {
       //some conditions, test's etc.

       //run first operation on list
       // RUNNING A THREAD, still ok
       if(...) threads.front()->Dispatch(this, nsIEventTarget::DISPATCH_NORMAL); 
    }

    //if this method is used by another thread+db query, 
    //then other operations can't run and need to wait
    //operations are stored and supported like fifo
    NS_IMETHODIMP nsDBService::Run(void)
    {
       //some other operations
       //real db operations in background

       int32_t phase = 3; //endphase
       int32_t code  = 0; //ok
       const char *msg = "OK";

       nsIDBCallback *callback = callbacks.pop();
       //wrapping callback function with runnable interface
       nsIRunnable   *runCallback = new nsResultCallback(callback, 
                                                         phase, 
                                                         code, 
                                                         msg);
       //routing event to main thread
       NS_DispatchToMainThread(runCallback, NS_DISPATCH_NORMAL); 

       runOperationIfNotBussy();
    }

    //nsResultCallback.h
    class nsResultCallback: public nsRunnable
    { 
    public:
       NS_DECL_ISUPPORTS
    public:
       NS_DECL_NSIRUNNABLE

    private:
       nsIDBCallback* callback;
       int32_t        resPhase;
       int32_t        resStatus;
       const char*    resMessage;

    public:
       nsResultCallback(nsIDBCallback* callback, 
                        int32_t phase, 
                        int32_t status, 
                        const std::string &message)   
          : callback(callback), 
            resPhase(phase), 
            resStatus(status), 
            resMessage(c_str_clone(message.c_str())) {};
       ~nsResultCallback();

    };

    //nsResultCallback.cpp
    NS_IMETHODIMP nsResultCallback::Run(void)
    {
       nsresult rv = NS_ERROR_FAILURE;
       try 
       {
          // APP HANDS AND CRUSH ! 
          if(this->callback) this->callback->OnInfo(resPhase, resStatus, resMessage);
       }
       catch(...) 
       {
          rv = NS_ERROR_UNEXPECTED;
          ERRF("nsBackpack::Run call method OnInfo from callback failed");
       }
       return rv;
    }

INVOCATION

    // *.js
    nsDBService.query("SELECT * FROM t", function(phase, code, mes) {
       //some UI actions or others db queries
    });

问题:

代码执行时应用程序冻结和崩溃如下所示:

    nsDBService::Query //main thread ok
    nsDBService::runOperationIfNotBussy //main thread
    nsDBService::threads.front()->Dispatch //run bg thread
    nsDBService:Run //bg thread
    NS_DispatchToMainThread //main thread
    nsResultCallback::Run //main thread
    nsIDBCallback::OnInfo //main thread, crash

如果代码执行看起来像这样,一切都很好:

                                                                                                       


nsDBService::Query //main thread ok
NS_DispatchToMainThread //main thread
nsResultCallback::Run //main thread
nsIDBCallback::OnInfo //main thread ok


题:

当从NS_DispatchToMainThread调用nsIDBCallback并从其他线程调用NS_DispatchToMainThread然后主应用程序线程,然后执行失败,我错过了什么,不明白？或者后台任务的另一种方法是什么？

    

Answer 1

无法重现，因为您没有提供独立的完整示例，因此请添加一些注释：

我注意到的第一件事是 的跨线程访问std::vector。您在评论中写了一些有关互斥锁的内容，所以这可能没问题。

肯定错误的是存储原始指针nsIDBCallback。XPCOM 对象是引用计数的。因此，一旦您的方法返回，如果没有其他引用，Query底层对象可能会被删除，从而在向量中留下一个悬空指针。delete我想这就是这里正在发生的事情！您需要保持对象处于活动状态，直到线程完成它，最好将其放入某处nsCOMPtr<nsIDBCallback>，例如放在nsCOMPArray<nsIDBCallback>.

PS：事实证明这是一个有点老的问题，我错过了......很抱歉延迟回答它：p