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I'm curious as to whether there is a lock on memory allocation if two threads simultaneously request to allocate memory. I am using OpenMP to do multithreading, C++ code.
OS's: mostly linux, but would like to know for Windows and Mac as well.
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In C, the library function malloc is used to allocate a block of memory on the heap. The program accesses this block of memory via a pointer that malloc returns.
All variables allocated by malloc (or new in C++) is stored in heap memory.
So, malloc uses a lock to make the threads "take turns" accessing malloc's internal structures.
The first time, malloc creates a new space (the heap) for the program (by increasing the program break location).
There could be improvements in certain implementations, such as creating a thread-specific cache (in this case allocations of small blocks will be lock-free). For instance, this from Google. But in general, yes, there is a lock on memory allocations.
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