When working with multithreaded applications in C++, especially on the Windows platform, understanding the different thread creation functions available is crucial. This article will delve into the differences and similarities between _beginthread, _beginthreadex, and CreateThread, three prevalent APIs used to create threads in Windows applications.

Understanding Windows Threading

In Windows, threading is a fundamental concept that allows applications to perform multiple tasks concurrently. Each thread runs independently and can execute code that is within the same process. When creating threads in Windows with C++, programmers have various options, each with its own use case and implications.

Thread Creation Functions

1. _beginthread

_beginthread is a function provided by the C Runtime Library (CRT) to create a new thread. It's specifically designed to work with the runtime library's data structures, ensuring proper handling of the thread's environment.

• Prototype:

1  uintptr_t _beginthread(
2      void( __cdecl *start_address )( void * ),
3      unsigned stack_size,
4      void *arglist
5  );

• Features:
  • Automatically initiates the C runtime for the new thread: This is essential if your thread will interact with any C runtime library functions.
  • Easy to use: Requires minimal setup as it automatically manages the thread environment.
  • Lack of fine-grained control: Does not provide as much control over thread attributes as _beginthreadex.
• Use Case: Simple threading requirements where the thread needs to interact with the CRT, and there's no need for advanced thread management.
• Example:

1  void __cdecl MyThreadFunction(void* data)
2  {
3      // Thread processing...
4  }
5
6  int main()
7  {
8      _beginthread(MyThreadFunction, 0, NULL);
9      // Continue with main thread processing...
10  }

2. _beginthreadex

_beginthreadex is an extended version of _beginthread that provides more control over how threads are created and managed.

• Prototype:

1  uintptr_t _beginthreadex(
2      void *security,
3      unsigned stack_size,
4      unsigned (__stdcall *start_address)(void *),
5      void *arglist,
6      unsigned initflag,
7      unsigned *thrdaddr
8  );

• Features:
  • Improved control: Offers more parameters, allowing for security attributes, stack size customization, initialization flags, and access to the thread identifier.
  • Returns a thread handle: Provides a handle to the created thread, allowing for more sophisticated thread management, such as waiting for the thread to finish using synchronization primitives.
  • C runtime initialization: Like _beginthread, it initializes the C runtime for the created thread.
• Use Case: Scenarios requiring more control over thread creation, such as modifying security attributes or needing access to the thread's identifier.
• Example:

1  unsigned __stdcall MyThreadFunctionEx(void* data)
2  {
3      // Thread processing...
4      return 0;
5  }
6
7  int main()
8  {
9      unsigned threadID;
10      HANDLE hThread = (HANDLE)_beginthreadex(NULL, 0, MyThreadFunctionEx, NULL, 0, &threadID);
11      WaitForSingleObject(hThread, INFINITE);
12      CloseHandle(hThread);
13  }

3. CreateThread

CreateThread is part of the Windows API, independent of the CRT, allowing for direct creation of threads without automatically initializing the C runtime.

• Prototype:

1  HANDLE CreateThread(
2      LPSECURITY_ATTRIBUTES lpThreadAttributes,
3      SIZE_T dwStackSize,
4      LPTHREAD_START_ROUTINE lpStartAddress,
5      __drv_aliasesMem LPVOID lpParameter,
6      DWORD dwCreationFlags,
7      LPDWORD lpThreadId
8  );

• Features:
  • Independent of CRT: Allows creating threads without automatic C runtime initialization, which is useful if threads exclusively use Windows API functions.
  • Rich functionality: Offers comprehensive control over thread creation, including setting security attributes, customizing stack size, and specifying creation flags.
  • Requires cleanup: Users must ensure proper cleanup of the thread, typically using CloseHandle.
• Use Case: Suitable for applications where CRT functions are not necessary for the thread, or where there's a need for maximum control over thread attributes and lifecycle.
• Example:

1  DWORD WINAPI MyWinApiThreadFunction(LPVOID lpParam)
2  {
3      // Thread processing...
4      return 0;
5  }
6
7  int main()
8  {
9      DWORD threadId;
10      HANDLE hThread = CreateThread(NULL, 0, MyWinApiThreadFunction, NULL, 0, &threadId);
11      WaitForSingleObject(hThread, INFINITE);
12      CloseHandle(hThread);
13  }

Key Differences and Considerations

Here's a summarized comparison of the three thread creation methods:

Conclusion

Choosing the right thread creation function hinges on your application's specific needs. If full control and advanced functionality are necessary, CreateThread is a strong option, especially if the C runtime environment isn't required. However, for applications heavily reliant on the CRT, _beginthread and _beginthreadex provide seamless integration with the CRT and additional flexibility, respectively, making them preferable choices in those scenarios. Understanding these differences equips developers with the ability to make informed decisions, optimizing their applications for performance and reliability.