Message Queues in DisastrOS

What?

The project aims to add a message queue to DisastrOS, an operating system simulator written in C.

How?

The project was made possible through the use of some predefined functions in DisastrOS and the creation of a structure that models a Message Queue:

typedef struct {
  ListItem list;
  int id;
  int num_written;
  ListHead descriptors_ptrs;
  ListHead messages;
  ListHead waiting_to_read;
  ListHead waiting_to_write;
} MessageQueue;

An auxiliary structure was also created to model a Message:

typedef struct {
  ListItem list;
  char message[MAX_LEN_MESSAGE];
  int length;
} Message;

To allow the OS to manage these structures, four new system calls were implemented, enabling opening, closing, writing, reading, and destroying a Message Queue:

int disastrOS_openMessageQueue(int id, int mode)
int disastrOS_closeMessageQueue(int fd)
int disastrOS_MessageQueue_write(int id, char* write_buffer, int len)
int disastrOS_MessageQueue_read(int id, char* buf, int len)
int disastrOS_MessageQueue_destroy(int id)

These system calls have been appropriately added to the System Call Vector.

Finally, a control mechanism has been implemented to handle cases where:

• A Message Queue is full and a process wants to write to it → the process is placed in the waiting list.
• A Message Queue is empty and a process wants to read from it → the process is placed in the waiting list.

How to run?

In the constants.h file, the system can be configured as desired.

• Compilation command: make
• Execution command: ./disastrOS_test