Josh's CSUMB Learning BLOG

This week we covered concurrency using multithreaded programming with the POSIX api. Concurrency solves the problems of parallelism and avoiding i/o blocking. This is important to operating systems because it allows for better sharing of the hardware resources. Threads allow for independent execution context within a process. Each thread has its own program counter, stack, and registers, but they all share the same memory space. This gives them a lower cost to create. One thing to be careful about is critical sections of code where multiple threads need to access a shared resource. We can’t allow them to operate on that resource simultaneously or else we could have a race condition where the output depends on the timing of thread execution. When a program has different output from one run to another it is called indeterminate. To avoid this we use locks to isolate the shared data such that only one thread can access it at a time - mutual exclusion. Atomic operations are operations that...

  Josh Goldberg CST334 40_2262 Mar 30, 2026 This week we went deeper into paging and free space management. We reviewed the malloc() and free() library functions and how they manage memory allocation with a free list. The free list contains chunks that have a size and a pointer to the next free node in a linked list. Behind these functions are the mechanisms that satisfy the memory allocation policies. Splitting will split a chunk into two to right-size a chunk for an allocation request and keep the remainder fragment in the free chunk list. Coalescing is the inverse. It will merge adjacent free chunks to reduce small fragments. Each chunk has a header that indicates the next chunk, whether this chunk is free or not, and a magic number for integrity checks. Following the header is the actual chunk space to be allocated. When a free(ptr) is called with a pointer to space, it’s pointing at the free space. We find the header at ptr - sizeof(header_t). Allocator goals: correctness, spe...