IPC Programming Faculty of Computer Science and Engineering Ho chi Minh city University of Technology SinhVienZone.com https://fb.com/sinhvienzonevn Introduction  Inter-Process Communication  Sending messages between processes  Sharing information between processes  Synchronization SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT IPC  Communication Transferring message Sharing information Mechanisms: Pipe Signal Message queue Shared memory Socket RPC/RMI SinhVienZone.com Synchronization Solving confliction Processing order Mechanisms: Lock file Semaphore Mutex (pthread) https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT IPC Programming  Pipe  Signal SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Pipe  Processes communicate to each other using pipe through FIFO mechanism P0 write SinhVienZone.com read https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT P1 Pipe operations  Write: #include ssize_t write(int fd, const void *buf, size_t count)  Read: #include ssize_t read(int fd, const void *buf, size_t count) SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Pipe types  Unnamed pipe  Local  Used in processes having parent-child relation  Named pipe (FIFO)  Global  Used by any processes SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Unnamed pipe #include int pipe(int filedes[2]);  Return value:  0: if successful, two file descriptors filedes[0], filedes[1] will be stored in filedes  -1: if error and error code is stored in external errno variable SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Unnamed pipe filedes[1] P0 P1 filedes[0]  Unidirectional/half-duplex  filedes[0] is only used to read  filedes[1] is only used to write SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT #include #include #include #include int main() { int fp[2]; char s1[BUFSIZ], s2[BUFSIZ]; pipe(fp); Compile and execute $gcc unpipe.c -o unpipe $./unpipe Input: I Love Penguin From pipe> I Love Penguin $ if (fork()==0) { /* Child Write */ printf("\nInput: "); fgets(s1,BUFSIZ,stdin); s1[strlen(s1)]=0; close(fp[0]); write(fp[1],s1,strlen(s1)+1); } else { /*Parent Read*/ close(fp[1]); read(fp[0],s2,BUFSIZ); printf("\nFrom pipe> %s\n", s2); } return 0; } SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Named pipe  Similar to unnamed pipe  Notice:  Similar to a file on file system (directory entry, file permission)  Can be used on any processes  Can be created from a command on shell (using mknod command) SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Create named pipe  System call #include #include int mknod(const char *path,mode_t mode,dev_t dev);  C/C++ library call #include #include int mkfifo(const char *pathname, mode_t mode); SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT #include #include #include #include #include extern int errno; Compile and execute $gcc fifo.c -o fifo $./fifo Parent writes to FIFO1: Test1 Child reads from FIFO1: Test1 Child feedbacks on FIFO2: Test2 Feedback data from FIFO2: Test2 $ #define FIFO1 "/tmp/fifo.1" #define FIFO2 "/tmp/fifo.2" #define PERMS 0666 int main(){ char s1[BUFSIZ], s2[BUFSIZ]; int childpid, readfd, writefd; SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT if ((mknod(FIFO1, S_IFIFO | PERMS, (errno!=EEXIST)) { printf("can't create fifo1: %s", exit(1); } if ((mknod(FIFO2, S_IFIFO | PERMS, (errno!=EEXIST)) { unlink(FIFO1); printf("can't create fifo2: %s", exit(1); } if ((childpid=fork())