Function Number	Function Name	Arguments	Return Value
ACQUIRE_BUFFER = 1	Acquire Buffer	Buffer Number, PID	NIL
RELEASE_BUFFER = 2	Release Buffer	Buffer Number, PID	0 or -1
ACQUIRE_DISK = 3	Acquire Disk*	PID	NIL
ACQUIRE_INODE = 4	Acquire Inode	Inodeindex, PID	0 or -1
RELEASE_INODE = 5	Release Inode	Inodeindex, PID	0 or -1
ACQUIRE_SEMAPHORE = 6	Acquire Semaphore	PID	Semaphore Table Index or -1
RELEASE_SEMAPHORE = 7	Release Semaphore	Semaphore Table Index, PID	0 or -1
ACQUIRE_TERMINAL = 8	Acquire Terminal	PID	NIL
RELEASE_TERMINAL = 9	Release Terminal	PID	0 or -1

*Release function for the disk is implimented in the disk interrupt handler.

Acquire Buffer

Description : Acquire the buffer corresponding to buffer number given as input. Assumes a valid PID and a valid buffer number are given.

while ( Buffer is locked ){   /* Check the Locking PID field in the Buffer Status Table */
    Set state of the process as ( WAIT_BUFFER , Buffer Number );
    Call the switch_context() function from the Scheduler Module.
}

Lock the Buffer by setting the PID of the current process in the Locking PID field
in the Buffer Status Table ;

return;

Called by BufRead and BufWrite functions in the File Manager.

Release Buffer

Description : Release the buffer corresponding to buffer number given as input. Assumes a valid PID and a valid buffer number are given.

If PID given as input is not equal to the LOCKING PID in the Buffer Status Table, return -1.

Free the lock in the the Buffer Status Table entry corresponding to
the buffer Number; /* Set Locking PID field to -1 */

loop through the process table{ 
       if (the process state is ( WAIT_BUFFER , Buffer Number ) ){
             Set state of process as (READY , _ )
         } 
}
return 0;

Called by BufRead and BufWrite functions in the File Manager.

Acquire Disk

Description : Locks the disk device. Assumes that a valid PID is given as input.

while ( disk is locked ){        /* Check the Status field in the Disk Status Table. */
    Set state of the process as ( WAIT_DISK , - );
    Call the switch_context() function from the Scheduler Module.
}

Lock the disk by setting PID and the status field in the Disk Status Table.

return;

Called by BufRead and BufWrite functions in the File Manager and the exception handler for swap-in.

Acquire Inode

Description : Locks the Inode entry corresponding to the inodeindex given as input. Assumes a valid PID and a valid inode index are given.

while ( inode is locked ){   /* Check the Lock field in the File Status Table. */
    Set state of the process as ( WAIT_FILE , Inode Index );
    Call the switch_context() function from the Scheduler Module.
} 

If inode becomes invalid, return -1. /* File was deleted by the time the inode was acquired */

Lock the Inode by setting the Lock field in the File Status Table 
to the PID of the current process.;

return 0;

Called by Delete, Read, Write and Seek system calls.

Release Inode

Description : Frees the lock of the inode entry corresponding to the inodeindex given as input. Assumes a valid PID and a valid inode index are given.

If PID given as input is not equal to the LOCKING PID in the File Status Table, return -1.

Free the lock in the File Status Table corresponding to the inode index;       /* Set the Lock field to -1 */

loop through the process table{ 
       if (the process state is ( WAIT_FILE, Inode Index ) ){
             Set state of process as (READY , _ )
         } 
}
return 0;

Called by Read, Write and Seek system calls.

Acquire Semaphore

Description : Acquires a semaphore and returns it's semaphore number. Assumes a valid PID is given as input. Returns -1 upon failure.

 

Find the index of a free entry in Semaphore table. If no free entry, return -1.
/* Free entry is indicated by a Process Count of 0. */ 

Set the PROCESS_COUNT to 1 and LOCKING_PID to -1.

Return the Semaphore table index.   /* success */

Called by the Semget system call.

Release Semaphore

Description : Releases a semaphore. Assumes a valid PID and semaphore table index are given as input.

 
If ( semaphore is locked by the current process)   /*Check the Locking PID in the Semaphore table*/
	Set the Locking PID to -1.  /* Unlock the semaphore before release */
	loop through the process table{ /*wake up processes blocked by the semaphore */
       		if (the process state is ( WAIT_SEMAPHORE, SEMTABLEINDEX ) ){
             	Set state of process as (READY , _ )
         	} 
	}

Decrement the process count of the semaphore in the semaphore table.
/* When the count becomes 0, the semaphore is free. */
	     

Called by the Semrelease and exit system call.

Acquire Terminal

Description : Locks the Terminal device. Assumes a valid PID is given as input.

while ( Terminal device is locked ){    /* Check the Status field in the Terminal Status Table */
    Set state of the process as ( WAIT_TERMINAL , - );
    Call the switch_context() function from the Scheduler Module.
}
    
Lock the Terminal device by setting the Status and PID fields in the Terminal Status Table.

return;

Called by the Terminal Read and Terimnal Write functions of the Device Manager Module.

Release Terminal

Description : Frees the Terminal device. Assumes a valid PID is given as input.

    If PID given as input is not equal to the LOCKING PID in the Teminal Status Table, return -1.

    Release the lock on the Terminal by updating the Terminal Status Table.;

    loop through the process table{ 
       if (the process state is ( WAIT_TERMINAL , - ) ){
             Set state of process as (READY , _ )
         } 
    }

    Return 0
 

Called by the Terimnal Write function in the Device Manager Module.