Multi-Threaded Server with Shared Queue in C

This C code template outlines a multi-threaded server employing shared queues for concurrent client handling. The program initializes semaphores to synchronize critical sections, defines structs for requests and parameters, and includes placeholders for required fields. Functions for queue initialization, adding/retrieving requests, and worker thread logic are outlined. The main function establishes a server socket, accepts connections, and manages client connections. Notably, some parts are marked for implementation, emphasizing the need for custom logic. Overall, the code serves as a robust foundation for developing a scalable concurrent server in C.

Crafting Scalable Concurrent Servers in C

This C code template lays the groundwork for a concurrent server with shared queues, employing multi-threading for efficient client handling. Robust synchronization mechanisms, such as semaphores, protect critical sections, while defined structs provide a blueprint for structuring requests and parameters. The template includes essential functions for queue management and worker thread logic. While certain portions await custom implementation, this template serves as a valuable educational tool for students exploring multi-threaded server architectures in C. Aspiring developers can use this foundation to deepen their understanding of synchronization, socket programming, and thread management, offering practical help with their C assignment.

Block 1: Header and Macro Definitions

#define _GNU_SOURCE #include < stdio.h > #include < stdint.h > #include < stdlib.h > #include < sched.h > #include < signal.h > #include < sys/types.h > #include < sys/wait.h > #include < semaphore.h > #include "common.h"

• This block includes necessary headers and macro definitions.
• _GNU_SOURCE is defined to enable GNU extensions.
• Standard headers for input/output, integer types, memory allocation, process scheduling, and signal handling are included.
• Headers needed for inter-process communication (sys/types.h, sys/wait.h) and semaphore synchronization (semaphore.h) are included.
• The "common.h" header, which presumably contains shared structs and constants, is included.

Block 2: Macro and Constant Definitions

#define BACKLOG_COUNT 100 #define USAGE_STRING "Missing parameter. Exiting.\n" "Usage: %s -q -w \n" #define STACK_SIZE (4096)

• Defines the backlog count for pending connections (BACKLOG_COUNT).
• Defines a usage string for command-line parameter validation.
• Specifies the stack size for the worker threads.

Block 3: Mutexes and Synchronized printf Macro

sem_t * printf_mutex; #define sync_printf(...) \ do { \ sem_wait(printf_mutex); \ printf(__VA_ARGS__); \ sem_post(printf_mutex); \ } while (0)

• Declares a semaphore pointer for a mutex named printf_mutex.
• Defines a synchronized printf macro sync_printf using the printf_mutex semaphore to protect the printf statement in a multi-threaded environment.

Block 4: Queue and Request Meta-Struct Definitions

struct request_meta { struct request request; /* ADD REQUIRED FIELDS */ }; struct queue { /* ADD REQUIRED FIELDS */ }; struct connection_params { /* ADD REQUIRED FIELDS */ }; struct worker_params { /* ADD REQUIRED FIELDS */ };

• Defines a struct request_meta containing a member request of type struct request and any additional required fields.
• Declares a struct queue and structs connection_params and worker_params with placeholders for required fields.

Block 5: Queue Initialization Function

void queue_init(struct queue * the_queue, size_t queue_size) { /* IMPLEMENT ME !! */ }

• Declaration of a function queue_init for initializing a queue. The implementation is not provided.

Block 6: Add to Queue Function

int add_to_queue(struct request_meta to_add, struct queue * the_queue) { int retval = 0; /* QUEUE PROTECTION INTRO START --- DO NOT TOUCH */ sem_wait(queue_mutex); /* ... */ sem_post(queue_mutex); /* ... */ return retval; }

• Declaration of a function add_to_queue for adding a request to the shared queue. Uses semaphores for protecting the critical section.

Block 7: Get from Queue Function

struct request_meta get_from_queue(struct queue * the_queue) { struct request_meta retval; /* QUEUE PROTECTION INTRO START --- DO NOT TOUCH */ sem_wait(queue_notify); sem_wait(queue_mutex); /* ... */ sem_post(queue_mutex); /* ... */ return retval; }

• Declaration of a function get_from_queue for retrieving a request from the shared queue. Uses semaphores for protection.

Block 8: Dump Queue Status Function

void dump_queue_status(struct queue * the_queue) { /* QUEUE PROTECTION INTRO START --- DO NOT TOUCH */ sem_wait(queue_mutex); /* ... */ sem_post(queue_mutex); }

• Declaration of a function dump_queue_status for displaying the status of the queue. Uses semaphores for protection.

Block 9: Worker Main Function

int worker_main( void * arg ) { struct timespec now; struct worker_params * params = ( struct worker_params * )arg; / * ... * / }

• Declaration of the main logic for the worker thread.

Block 10: Start Worker Function

int start_worker(void * params, void * worker_stack) { /* IMPLEMENT ME !! */ }

• Declaration of a function start_worker that uses the clone() system call to start a worker thread.

Block 11: Connection Handling Function

void handle_connection(int conn_socket, struct connection_params conn_params) { /* IMPLEMENT ME!! */ }

• Declaration of the function handle_connection for managing client connections.

Block 12: Main Function

int main(int argc, char ** argv) { /* ... */ }

• Declaration of the main function. It includes the setup of a server socket, accepting connections, initializing synchronization primitives, and handling client connections.

Conclusion

In conclusion, the provided code serves as a foundation for a multi-threaded server designed to handle client connections efficiently. Employing semaphores for synchronization, the code ensures thread safety and protection of shared resources, essential for concurrent operations. The modular design, with functions dedicated to queue management, worker threads, and connection handling, enhances code readability and maintainability. However, key functionalities, marked as "IMPLEMENT ME," indicate the need for additional code to complete the server's robust implementation. This template offers a structured starting point for developing a scalable and responsive server system, with the potential for further customization and expansion based on specific requirements.