Inter Process Communication through shared memory is a concept where two or more process can access the common memory. And communication is done via this shared memory where changes made by one process can be viewed by anther process.
The problem with pipes, fifo and message queue – is that for two process to exchange information. The information has to go through the kernel.
- Server reads from the input file.
- The server writes this data in a message using either a pipe, fifo or message queue.
- The client reads the data from the IPC channel,again requiring the data to be copied from kernel’s IPC buffer to the client’s buffer.
- Finally the data is copied from the client’s buffer.
- Concurrent Merge Sort in Shared Memory
- fork() and memory shared b/w processes created using it
- Operating System | Peterson's Algorithm (Using processes and shared memory)
- Working with Shared Libraries | Set 2
- Working with Shared Libraries | Set 1
- Difference between Static and Shared libraries
- Inter-process Communication using a shared stack
- Introduction to memory and memory units
- Secondary Memory
- Types of computer memory (RAM and ROM)
- Memory Layout of C Programs
- What is Memory Leak? How can we avoid?
- Virtual Memory | Questions
- How to deallocate memory without using free() in C?
- Stack vs Heap Memory Allocation
A total of four copies of data are required (2 read and 2 write). So, shared memory provides a way by letting two or more processes share a memory segment. With Shared Memory the data is only copied twice – from input file into shared memory and from shared memory to the output file.
SYSTEM CALLS USED ARE:
ftok(): is use to generate a unique key.
shmget(): int shmget(key_t,size_tsize,intshmflg); upon successful completion, shmget() returns an identifier for the shared memory segment.
shmat(): Before you can use a shared memory segment, you have to attach yourself
to it using shmat(). void *shmat(int shmid ,void *shmaddr ,int shmflg);
shmid is shared memory id. shmaddr specifies specific address to use but we should set
it to zero and OS will automatically choose the address.
shmdt(): When you’re done with the shared memory segment, your program should
detach itself from it using shmdt(). int shmdt(void *shmaddr);
shmctl(): when you detach from shared memory,it is not destroyed. So, to destroy
shmctl() is used. shmctl(int shmid,IPC_RMID,NULL);
SHARED MEMORY FOR WRITER PROCESS
SHARED MEMORY FOR READER PROCESS
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