Programming: Windows Threading Vs Linux Threading (Part 2)

This is in continuation of the previous article 'Windows Threading Vs. Linux Threading', here we'll see a subtle but significant difference in the thread start routine which gets a call from CreateThread() API in the Windows world or pthread_create() function call in the Linux world.

The ThreadProc function in Windows:

DWORD WINAPI ThreadProc(
_In_ LPVOID lpParameter
);

This is an application-defined function that serves as the starting address for a thread.

Note: As per MSDN, Do not declare this callback function with a void return type and cast the function pointer to LPTHREAD_START_ROUTINE when creating the thread.
Code that does this is common, but it can crash on 64-bit Windows.

The return value indicates the success or failure of this function. The return value should never be set to STILL_ACTIVE (259).

In Linux: The function passed as start_routine in the pthread_create() function should correspond to the following C function prototype:
void *threadStartRoutinName(void *);

This is one of the differences we need to take care of while writing thread start routines between Windows and Linux.

Comments

XOR (Exclusive OR) for branchless coding

The following example shows the array reversing using the XOR operator . No need to take any additional variable to reverse the array. int main(int argc, _TCHAR* argv[]) { char str[] = "I AM STUDENT"; int length = strlen(str); for(int i = 0; i < ((length/2)); i++) { str[i] ^= str[length - (1+i)]; str[length - (1+i)] ^= str[i]; str[i] ^= str[length - (1+i)]; } cout << str << endl; return 0; } The above example is one of the uses of XOR but XOR comes in handy when we can do branchless coding methods like butterfly switch etc. Sometimes this is very effective in speeding up the execution. Let's see one of the uses of XOR in branchless coding. I am taking a simple example of Y = | X |. Yes, I am generating abs of a supplied number. So, my function signature/definition in C++ looks like below: int absoluteBranch( int x) { if (x < 0 ) { return ...

Reversing char array without splitting the array to tokens

I was reading about strdup, a C++ function and suddenly an idea came to my mind if this can be leveraged to aid in reversing a character array without splitting the array into words and reconstructing it again by placing spaces and removing trailing spaces. Again, I wanted an array to be passed as a function argument and an array size to be passed implicitly with the array to the function. Assumed, a well-formed char array has been passed into the function. No malformed array checking is done inside the function. So, the function signature and definition are like below: Below is the call from the client code to reverse the array without splitting tokens and reconstructing it. Finally, copy the reversed array to the destination. For GNU C++, we should use strdup instead _strdup . On run, we get the following output: Demo code

Power of Two

I n this post will be discussing how to calculate if a number is a power of two or not. As an example, 8 is a power of two but the number 10 is not. There are many ways we can solve this. First , we will take an approach which is simple and iterative. In this case, we will calculate the power of two one by one and check with the supplied number. The below code illustrates it. bool isPowerofTwo(unsigned num) { auto y = 1; while (0 != y) { if (num == y) return true; if (num < y) return false; y <<= 1; } return false; } Second , assuming, the number is a 32-bit number, this is also an iterative solution. In this scenario, iterating all bits and counting the set bits. Any number which is a power of 2 will have only one bit set and the rest will be zeros. As an example, 8 in binary representation is 1000. Using this observation, we can implement an iterative solution. bool isPowerofTwo(unsigned num) { auto one_count = 0; for (auto index = 0; index < ...

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