I am working on a primitive project ported on AIX Unix Box. Earlier this system used to run on VMS VAX and DEC Alpha system. The major source code files are written in FROTRAN.

Across process data are exchanged through FROTRAN COMMONS and a specific locking mechanism is implemented for resource synchronization. Data for exchange are stored in FROTRAN Array in COMMONS. During addition to the bottom of the array and removal from the top, a specific position of the array is marked as 1 or 0 meaning that array can be accessed or cannot. Based upon these values the action on arrays would be taken. I hope that I am clear.

They used LIB$BBSSI() system call to lock the list and LIB$BBCCI() system call to release the list from lock state in VMS. I presume that this would be atomic cause of which process where in synchronization.

During porting of the same software in Tru64 they swapped the same routines with C subroutines _TESTBITSSI() and _TESTBITCCI() calls.

The problem came when they ported it to AIX. Due to lack of technology specifications we are unable to have atomic locking mechanism. Hence the issue is that two or more process is able to detect that they can act on a same array resulting on an unpredictable behavior.

We need a solution for the problem. I though of a solution but I don't know that in multi-process environment whether the solution would work or not. Please provide your necessary input and ensure that the code does leads to a DEADLOCK.
:

During the process startup we would store the required address our interest. Say for example we have 3-array list and list lock index is 1. So if the arrays are named as A, B, D then we will store the address of A (1), B (1) and D (1) in ‘C' array of pointers *list_arr[3] (list_arr[0], list_arr[1], list_arr[2]).
Now LOCK() and REL() subroutine would be called across process running in different address space.

LOCK(int *bit_pos, int *address)
{
.......
.......
/* For One specific address */
RERUN:
if ( address == list_arr[0] )
{
if ( shared_variable_One == 0 ) /* Variable Shared Across Processes */
{
shared_variable_One = getpid ( ) ;
}
if (shared_variable_One == getpid ( ) )
{
if ( ++ shared_variable_two > 1 ) /* Variable Shared Across Processes Initially initialized as 0*/
goto RERUN:
/* Set the bit value */
shared_variable_One = 0 ;
shared_variable_two = 0 ;
}
else
goto RERUN;
}

.......................
.......................
}
The same can be implemented for REL(int *bit_pos, int *address).

These subroutines would then be called through FROTANS subroutines.

I have had thought about using SEMAPHORES but then we had to use 3 semaphores (as in this example) such that operation on one address by one process does not blocks operation on other address which is being accessed by multiple process.

Thanks in advance.