This repository contains three Operating Systems assignments developed in C, each graded 10/10 at the Technical University of Cluj-Napoca. The projects explore key low-level system programming concepts such as file parsing using raw system calls, advanced process/thread synchronization, and inter-process communication via shared memory and named pipes.

Implements a Linux command-line utility to:

• Recursively list directory contents with support for filtering by file size (size_smaller) and file name prefix (name_starts_with).
• Parse a custom binary file format called SF (Section File) by interpreting a binary header and validating fields like:
  • MAGIC, VERSION, NO_OF_SECTIONS, SECTION_TYPE
• Extract lines from specific sections using byte-level offset calculations.
• Traverse directory trees and identify all valid SF files that contain only sections smaller than 1273 bytes.

📌 System-level highlights:

• Uses only low-level POSIX system calls (open(), read(), lseek(), close(), opendir(), readdir()) — no fopen() or fscanf().
• Implements robust binary parsing logic (headers + sections) using manual byte offset navigation and validation.
• Handles edge cases like malformed files, invalid magic/version, or incorrect section configurations.

Builds a complex process tree (7 processes) and implements fine-grained thread synchronization using:

• pthread_create() for thread management
• POSIX semaphores and mutexes/condition variables for synchronization
• Proper fork() process isolation and parent-child lifecycle control

📌 Key constraints implemented:

• Process P5 spawns 38 threads, enforcing a strict limit of max 6 concurrent running threads (true concurrency control, not creation cap).
• Implements thread barrier semantics: T5.11 must terminate while exactly 6 threads are active.
• Cross-process synchronization between P6 and P7 threads:
  • T7.6 must terminate before T6.1 starts.
  • T7.3 must start only after T6.1 terminates.
• Process P6: T6.4 starts before T6.2, and ends after it — demonstrating ordered thread dependency control.

📌 Testing interface integration: All processes and threads communicate with the evaluator using init() and info(BEGIN/END, PID, TID) hooks, ensuring synchronization constraints are externally verifiable.

Implements a protocol-based inter-process communication server using:

• POSIX named pipes (FIFOs): bidirectional communication with a tester client
• POSIX shared memory (shm_open, ftruncate, mmap) for data exchange
• Memory-mapped files for reading binary SF file content with performance in mind

📌 Supported operations via command protocol:

• CONNECT, PING, CREATE_SHM: Establish pipe communication and initialize shared memory region (2.4MB).
• MAP_FILE, WRITE_TO_SHM, READ_FROM_FILE_OFFSET: Efficient file I/O using memory mapping, no direct read() on files allowed.
• READ_FROM_FILE_SECTION: Extracts a number of bytes from a given section and offset in a SF-format file.
• READ_FROM_LOGICAL_SPACE_OFFSET: Calculates logical memory layout using 3072-byte alignment between sections, simulates virtual file mapping, and reads data at calculated logical offsets.

📌 System-level constraints:

• Must validate offsets and bounds before memory access.
• Penalized for fallback to read() instead of mmap access.
• Follows strict protocol format using string/number fields with special terminators (e.g., #), implementing a custom low-level protocol parser.

• C (C89/C99 standard)
• Linux system programming: file descriptors, directory traversal, memory-mapped I/O
• POSIX threads & synchronization: pthread, sem_t, mutex, condition variables
• IPC mechanisms: named pipes (FIFOs), shared memory, and memory-mapped files
• Custom protocol implementation: byte-wise parsing and encoding of messages

These assignments were developed in the context of the Operating Systems course in Year 3 of my Computer Science degree. The focus was on mastering systems programming by solving real-world tasks with low-level control over execution and memory.

I am highly passionate about this field and consistently excelled in it — each of these assignments was awarded the maximum grade of 10/10.

Francesco Maxim

• Student @ UTCN, Faculty of Automation and Computer Science
• Email: maaximfrancesco@gmail.com
• GitHub: maxim-francesco
• LinkedIn: linkedin.com/in/francescomaxim

💡 If you're passionate about systems programming, feel free to connect! I'm always open to collaboration and low-level development challenges.