Windows平台下的多线程编程(计算机论文翻译)

附录A Under the Windows platform multi threaded programming A thread is a process execution path it contains separate stack and CPU register state the process of each thread to share all resources including open files signal identification and dynamic allocation of memory and so on All threads within a process using the same address space and these threads of execution by the system scheduler control thread scheduler to decide which and when to execute the executable threads Thread has priority lower priority thread must wait until the higher priority thread after their implementation In the multi processor machines the scheduler can be multiple threads running up into different processors it will give the processor the task balance and improve efficiency of the system Windows is a multitasking operating system a process in Windows contains one or more threads 32 bit Windows environment Win32 API provides a multi threaded application development interface functions required and use of VC in the standard C libraries are also provided to develop multithreaded applications the corresponding MFC class library encapsulates the class of multi threaded programming users in the development can be based on the needs and characteristics of the application select the appropriate tool In order so that we can fully understand the Windows multi threaded programming techniques this article will focus on Win32 API and MFC are two ways of how to prepare multi threaded programs Multithreaded Programming in Win32 and MFC class library under way to support the principle is the same the main thread of the process at any time needed to create a new thread When the thread has finished automatically terminate the thread when the process is complete all threads are terminated Threads share the process of all activities of resources therefore be considered when programming multiple threads access the same resource conflict problem When a thread is accessing a process object and another thread to change the object it may produce incorrect results programming to solve this conflict Under the multi threaded Win32 API programming Win32 API is the Windows operating system kernel and the interface between applications which will provide the functions of the kernel function wrapper the application obtained by calling the correlation function of the corresponding system function In order to provide multi threading applications Win32 API function provides some focus on procedures for handling multi threaded set of functions Directly with the Win32 API to program design has many advantages Win32 based application code execution is small high efficiency but it requires programmers to write code more and all systems need to manage the resources available to the program Programming with the Win32 API directly on the Windows system kernel programmer is required to have a certain understanding it will take a lot of time on the programmer to manage system resources thus reducing the efficiency of the programmer 1 With the Win32 function to create and terminate threads Win32 function library provides a function of multi threaded operation including creating threads terminate threads the establishment of exclusive zones In the application s main thread or other activities to create a new thread thread function is as follows HANDLE CreateThread LPSECURITY ATTRIBUTES lpThreadAttributes DWORD dwStackSize LPTHREAD START ROUTINE lpStartAddress LPVOID lpParameter DWORD dwCreationFlags LPDWORD lpThreadId HANDLE CreateThread LPSECURITY ATTRIBUTES lpThreadAttributes DWORD dwStackSize LPTHREAD START ROUTINE lpStartAddress LPVOID lpParameter DWORD dwCreationFlags LPDWORD lpThreadId If you create a successful thread handle is returned otherwise NULL Create a new thread the thread started to execute However if used in dwCreationFlags CREATE SUSPENDED property then the thread is not immediately executed but the first suspended until the calls started after ResumeThread threads in the process can call the following function to set the priority of the thread BOOL SetThreadPriority HANDLE hThread int nPriority BOOL SetThreadPriority HANDLE hThread int nPriority When the function returns the calling thread the thread automatically terminates If you need to terminate during the execution of the thread can call the function VOID ExitThread DWORD dwExitCode VOID ExitThread DWORD dwExitCode If you terminate a thread in the thread on the outside you can call the following function BOOL TerminateThread HANDLE hThread DWORD dwExitCode BOOL TerminateThread HANDLE hThread DWORD dwExitCode It should be noted this function may cause system instability and the thread does not release the occupied resources Therefore under normal circumstances it is recommended not to use this function If you want to terminate the thread is the last thread within the process the thread is terminated after the corresponding process should be terminated 2 Thread synchronization In the thread body if the thread is completely independent data access with other threads and other resources without conflict operation the method can be carried out in accordance with generally single threaded programming However the situation in multi threaded processing is often not the case often between threads simultaneously access some resources Because access to shared resources causes conflict is inevitable in order to address this thread synchronization problems Win32 API provides a variety of synchronization objects to help programmers access to shared resources to resolve the conflict In presenting these synchronization objects introduce wait functions before because all the control object s access control should use this function Win32 API provides a set of threads can block waiting for the implementation of its own function These functions in its argument object generates one or more synchronization signal or exceeds the waiting time will be returned Waiting function is not returned the threads in a wait state when the thread consumes very little CPU time Not only can guarantee the wait function using thread synchronization but also can improve the running efficiency Waiting function is the most commonly used DWORD WaitForSingleObject HANDLE hHandle DWORD dwMilliseconds DWORD WaitForSingleObject HANDLE hHandle DWORD dwMilliseconds The function can be used to simultaneously monitor multiple WaitForMultipleObject synchronization object the function is declared as DWORD WaitForMultipleObject DWORD nCount CONST HANDLE lpHandles BOOL bWaitAll DWORD dwMilliseconds DWORD WaitForMultipleObject DWORD nCount CONST HANDLE lpHandles BOOL bWaitAll DWORD dwMilliseconds 1 mutex object Mutex state of the object by any thread in that it does not have a time signal it was a time when no signal Mutex objects are suitable for coordination of multiple threads exclusive access to shared resources The following steps can use the object First create a mutex object get the handle HANDLE CreateMutex HANDLE CreateMutex Then in the thread before the possible areas of conflict ie before access to shared resources calls WaitForSingleObject the handle to the function the request takes mutex object dwWaitResult WaitForSingleObject hMutex 5000L dwWaitResult WaitForSingleObject hMutex 5000L Shared resources conclusion of the visit the release of the occupation of the mutex object ReleaseMutex hMutex ReleaseMutex hMutex Mutex object at the same time can only be occupied by a thread when the mutex object is occupied by a thread when another thread would like to take it if you must wait until after the release of the previous thread to succeed 2 signal object Signal objects allow multiple threads simultaneously access shared resources in the creation of object may also specify the maximum number of threads access When a thread successfully apply for access to the signal by a counter object call ReleaseSemaphore function the signal object counter plus one Among them the counter value is greater than or equal to 0 but less than or equal to the maximum specified when created If an application to create a signal object the initial value of its counter is set to 0 to block the other thread to protect the resources And other initialization is complete call ReleaseSemaphore function will increase to its maximum value the counter you can access a normal visit The following steps can use the object First create the signal object HANDLE CreateSemaphore HANDLE CreateSemaphore A signal or open object HANDLE OpenSemaphore HANDLE OpenSemaphore Then access to shared resources in the thread before calling WaitForSingleObject After access to shared resources should be occupied by the release of the signal objects ReleaseSemaphore 3 the event object Event object Event is the simplest synchronization objects which includes both signal and no signal state Threads access a resource you need to wait for some event to occur then the most appropriate to use the event object For example only the data received in the communication port buffer the monitor thread is activated The event object is created with CreateEvent function This function can be specified event object class and the initial state of the event If the manual reset event it always maintained a signal pick like Ba Ban esetEvent function reset to no signal events If the event is automatically reset then its state after the release of a single waiting thread will automatically become free signal SetEvent With SetEvent can set the event object to signaled OpenEvent In the establishment of event named for the object so that other threads in the process can be used to open the specified function name OpenEvent event object handle 4 exclusion zone object Asynchronous execution in the exclusion zone it can only be in the same process of dealing with shared resources between threads At a time when several methods described above can be used however the use of exclusion zones approach makes more efficient synchronization management CRITICAL SECTION used to define a structure of exclusion zone object is called before the process using the following function to initialize the object VOID InitializeCriticalSection LPCRITICAL SECTION VOID InitializeCriticalSection LPCRITICAL SECTION When a thread uses the exclusion zone call the function EnterCriticalSection or TryEnterCriticalSection When asked to take exit exclusion zone call the function LeaveCriticalSection the release of the exclusion zone occupied by the object for other threads MFC based multi threaded programming Microsoft s VC MFC is to provide an integrated environment based library for programmers it uses the class library to encapsulate Win32 API way to class provided to developers Because of its fast simple powerful and so loved by the majority of developers Therefore it is recommended to use MFC class library application development In VC with the MFC class library provides support for multithreaded programming basic principles and design based on the same Win32 API but MFC synchronization objects on a wrapper so to achieve more convenient to avoid the object handle management the tedious work In MFC the thread is divided into two types worker threads and user interface thread Work earlier in the thread with the same thread the thread is a user interface to receive user input handle events and message threads 1 Worker thread Relatively simple work thread programming design ideas and the mentioned earlier the same a basic function represents a thread create and start the thread the thread into the running state if the thread is used to share resources the need for resource synchronization In this way create a thread and start the thread can call the function CWinThread AfxBeginThread AFX THREADPROC pfnThreadProc LPVOID pParam int nPriority THREAD PRIORITY NORMAL UINT nStackSize 0 DWORD dwCreateFlags 0 LPSECURITY ATTRIBUTES lpSecurityAttrs NULL UINT ThreadFunction LPVOID pParam CWinThread AfxBeginThread AFX THREADPROC pfnThreadProc LPVOID pParam int nPriority THREAD PRIORITY NORMAL UINT nStackSize 0 DWORD dwCreateFlags 0 LPSECURITY ATTRIBUTES lpSecurityAttrs NULL parameter pfnThreadProc is the thread of execution function prototype is UINT ThreadFunction LPVOID pParam Parameter is passed to the implementation of pParam argument Parameter is the thread nPriority rights optional values HREAD PRIORITY NORMAL THREAD PRIORITY LOWEST THREAD PRIORITY HIGHEST THREAD PRIORITY IDLE THREAD PRIORITY NORMAL THREAD PRIORITY LOWEST THREAD PRIORITY HIGHEST THREAD PRIORITY IDLE Parameter dwCreateFlags is a sign of the thread is created you can value CREATE SUSPENDED that thread is created in a suspended state called ResumeThread thread continues to run after the function or the value of 0 indicates a thread is created after running CWinThread class object return value is a pointer its member variables m hThread for the thread handle in the way of Win32 API functions that operate under the parameters of the thread are required to provide a handle to the thread so when the thread is created you can use all the Win32 API function pWinThread m Thread thread related operations Note If a class object to create and start the thread the thread function should be defined as global functions outside the class 2 The user interface thread MFC based applications have an application object which is CWinApp derived class object that represents the application process the main thread When the thread and exit the thread is executed because no other threads in the process the process ends automatically Class C W inApp derived from the C W inThread C W inThread user interface thread is the basic class We write the user interface thread you need to derive from C W inThread thread of our own class ClassWizard can help us do this work First use ClassWizard to derive a new class set the base class CwinThread Note The class DECLARE DYNCREATE and IMPLEMENT DYNCREATE macros are necessary because you need to create threads dynamically created class object Necessary initialization and exit code can be placed in the class respectively and ExitInstance function InitInstance If you need to create a window can be done in the InitInstance function And then create a thread and start the thread Two methods can be used to create the user interface thread MFC provides two versions of the AfxBeginThread function one used to create the user interface thread The second method is divided into two steps first the calling thread class constructor creates a thread object Second call CWinThread CreateThread function to create the thread After the establishment and start the thread the thread function in the process of implementation has been effective If the thread object the object is deleted before the end of the thread CWinThread thread has completed the end of our work 3 Thread Synchronization Earlier we introduced the Win32 API provides several objects related to thread synchronization in the MFC class library in a few objects in the class of this package they have a common base class CSyncObject their correspondence to Semaphore corresponding CSemaphore Mutex corresponding CMutex Event corresponding CEvent CriticalSection corresponding CCriticalSection In addition MFC functions of the two also had to wait for packages that CSingleLock and CMultiLock Similar to the four objects for use in the example here to illustrate CMutex Create a CMutex object CMutex mutex FALSE NULL NULL CMutex mutex FALSE NULL NULL Or CMutex mutex When each thread to access shared resources using the following code CSingleLock sl CSingleLock sl sl Lock if sl IsLocked Operate on shared resources sl Unlock Conclusion Here draw attention to is that in multi threaded programming to be especially careful when dealing with resource sharing and multi threaded debugging problems 附录B Windows 平台下的多线程编程平台下的多线程编程 信息工程系 2007 级计算机科学与技术黎向阳译 李仲生指导 线程是进程的一条执行路径 它包含独立的堆栈和 CPU 寄存器状态 每个 线程共享所有的进程资源 包括打开的文件 信号标识及动态分配的内存等 一个进程内的所有线程使用同一个地址空间 而这些线程的执行由系统调度程 序控制 调度程序决定哪个线程可执行以及什么时候执行线程 线程有优先级 别 优先权较低的线程必须等到优先权较高的线程执行完后再执行 在多处理 器的机器上 调度程序可将多个线程放到不同的处理器上去运行 这样可使处 理器任务平衡 并提高系统的运行效率 Windows 是一种多任务的操作系统 在 Windows 的一个进程内包含一个或 多个线程 32 位 Windows 环境下的 Win32 API 提供了多线程应用程序开发所 需要的接口函数 而利用 中提供的标准 库也可以开发多线程应用程序 相应的 类库封装了多线程编程的类 用户在开发时可根据应用程序的需 要和特点选择相应的工具 为了使大家能全面地了解 Windows 多线程编程技术 本文将重点介绍 Win32 API 和 MFC 两种方式下如何编制多线程程序 多线程编程在 Win32 方式下和 MFC 类库支持下的原理是一致的 进程的 主线程在任何需要的时候都可以创建新的线程 当线程执行完后 自动终止线 程 当进程结束后 所有的线程都终止 所有活动的线程共享进程的资源 因 此 在编程时需要考虑在多个线程访问同一资源时产生冲突的问题 当一个线 程正在访问某进程对象 而另一个线程要改变该对象 就可能会产生错误的结 果 编程时要解决这个冲突 Win32 API 下的多线程编程 Win32 API 是 Windows 操作系统内核与应用程序之间的界面 它将内核提 供的功能进行函数包装 应用程序通过调用相关函数而获得相应的系统功能 为了向应用程序提供多线程功能 Win32 API 函数集中提供了一些处理多线程 程序的函数集 直接用 Win32 API 进行程序设计具有很多优点 基于 Win32 的 应用程序执行代码小 运行效率高 但是它要求程序员编写的代码较多 且需 要管理所有系统提供给程序的资源 用 Win32 API 直接编写程序要求程序员对 Windows 系统内核有一定的了解 会占用程序员很多时间对系统资源进行管理 因而程序员的工作效率降低 1 用 Win32 函数创建和终止线程 Win32 函数库中提供了操作多线程的函数 包括创建线程 终止线程 建 立互斥区等 在应用程序的主线程或者其他活动线程中创建新的线程的函数如 下 HANDLE CreateThread LPSECURITY ATTRIBUTES lpThreadAttributes DWORD dwStackSize LPTHREAD START ROUTINE lpStartAddress LPVOID lpParameter DWORDdwCreationFlags LPDWORD lpThreadId 如果创建成功则返回线程的句柄 否则返回 NULL 创建了新的线程后 该线程就开始启动执行了 但如果在 dwCreationFlags 中使用了 CREATE SUSPENDED 特性 那么线程并不马上执行 而是先挂起 等到调用 ResumeThread 后才开始启动线程 在这个过程中可以调用下面这个函数来设置 线程的优先权 BOOL SetThreadPriority HANDLE hThread int nPriority 当调用线程的函数返回后 线程自动终止 如果需要在线程的执行过程中终止 则可调用函数 VOID ExitThread DWORD dwExitCode 如果在线程的外面终止线程 则可调用下面的函数 BOOL TerminateThread HANDLE hThread DWORD dwExitCode 但应注意 该函数可能会引起系统不稳定 而且线程所占用的资源也不释 放 因此 一般情况下 建议不要使用该函数 如果要终止的线程是进程内的最后一个线程 则线程被终止后相应的进程也应 终止 2 线程的同步 在线程体内 如果该线程完全独立 与其他线程没有数据存取等资源操作 上的冲突 则可按照通常单线程的方法进行编程 但是 在多线程处理时情况 常常不是这样 线程之间经常要同时访问一些资源 由于对共享资源进行访问 引起冲突是不可避免的 为了解决这种线程同步问题 Win32 API 提供了多种 同步控制对象来帮助程序员解决共享资源访问冲突 在介绍这些同步对象之前 先介绍一下等待函数 因为所有控制对象的访问控制都要用到这个函数 Win32 API 提供了一组能使线程阻塞其自身执行的等待函数 这些函数在 其参数中的一个或多个同步对象产生了信号 或者超过规定的等待时间才会返 回 在等待函数未返回时 线程处于等待状态 此时线程只消耗很少的 CPU 时 间 使用等待函数既可以保证线程的同步 又可以提高程序的运行效率 最常 用的等待函数是 DWORD WaitForSingleObject HANDLE hHan