Assignment  5  (Marks 10)

•    Date of assignment out: 07.09.2006 
  

•    Last date of report: 12.10.2006
  

•  You have to create a static library that supports calls similar to creation of unnamed pipes, read from the pipe and write to the pipe (on SUN SPARC). The functions to implement are int mypipe(int fd[]), int readpipe(int fd, char *buff, int noc), int writepipe(int fd, char *buff, int noc), int rmpipe(int fd[]).

•   The parent process will be compiled with the library. It will open the required number of 'pipes' and then it creates child processes where the library will be copied to the child processes. Child can use the opened 'pipes' for communication. A child can also create new 'pipes' which can be used by itself and its children. Naturally it cannot work with exec() call.
  

• int mypipe(int fd[]): called from the parent process acquires a shared memory and a set of semaphores. Stores the identifiers of the shared memory and the semaphore set in a global data structure of the library.   The shared memory is used as the buffer. The semaphores are used to ensure exclusive access to the shared buffer and also to check buffer-full and buffer-empty conditions. The function puts two identifiers in fd[0] (read) and fd[1] (write) to be used by other functions. It returns zero (0) on success and -1 on any error.

• int writepipe(int fd, char *buff, int noc): when called from the parent or any of its child (no exec) process, attatches the  shared memory  corresponding to the write identifier fd and writes noc bytes from the local buffer pointed by buff in the 'pipe', the shared memory. It should not write when the buffer is full and should implement critical section for exclusive access to the buffer. Both are to be achieved by the set of semaphores associated with the 'pipe'. After the writing, the shared memory is detached. Return values are similar to mypipe().

• int readpipe(int fd, char *buff, int noc): reads noc bytes from the 'pipe' (shared memory), identified by the read identifier fd, in the local buffer pointed by buff. It should not read from the empty buffer and should implement critical section for exclusive access to the buffer using the set of semaphores. After the reading is complete, the shared memory is detached. Return values are similar to mypipe().

• int rmpipe(int fd[]): removes the shared memory and the set of semaphores identified by the pair of read-write identifiers fd[0] and fd[1].  Return values are similar.

• The essential files are mypipe.h, mypipe.c The following commands show how to create a static library and how to link it with a user program.

                                     $ gcc -Wall -c mypipe.c
                              $ ar -qv libmypipe.a mypipe.o
                              $ gcc -Wall testMyPipe.c -L. -lmypipe

•  Prepare a Makefile that will take the user program testMyPipe.c as a parameter and will create the a.out file. Finally prepare the tar file <rollNo>_05.tar with mypipe.h, mypipe.c and the Makefile. Keep it in the proper directory. Do not change names or types of any of the function or files.