src/process2.c

   1 #include <stdio.h>
   2 /* exit.. */
   3 #include <stdlib.h>
   4 /* strsignal... */
   5 #include <string.h>
   6
   7 /* open/read/write/close */
   8 #include <fcntl.h>
   9
  10 /* Signals handling.. */
  11 #include <signal.h>
  12
  13 #include <sys/shm.h>
  14
  15 /** If buffer is too small to hold entire string, it is incremented by this value */
  16 #define BUFFER_STEP 16
  17
  18 /** Named pipe used to communicate with process1 */
  19 char * read_pipe = "/tmp/process1pipe";
  20
  21 /** Named pipe used to communicate with process3 */
  22 char * write_pipe = "/tmp/process2pipe";
  23
  24 /** Descriptor of input pipe */
  25 int read_descriptor;
  26
  27 /** Descriptor of output pipe */
  28 int write_descriptor;
  29
  30
  31 /**
  32  * Shared memory variables
  33  */
  34
  35 /**
  36  * Memory key for processes. Must be same between all processes to properly
  37  * communicate.
  38  */
  39 key_t shmkey = 18912;
  40 /**
  41  * Id of the shared memory
  42  */
  43 int shmid;
  44
  45 /**
  46  * Message shared by processes. Contains array of process IDs
  47  */
  48 struct message {
  49         pid_t pids[3];
  50 };
  51
  52 struct message * processes = NULL;
  53
  54 /**
  55  * Message queue variables
  56  */
  57 key_t qkey;
  58 int qid_input;
  59
  60 int qid_output1;
  61 int qid_output2;
  62
  63 struct queue_message {
  64         long mtype;
  65         int signo[1];
  66 };
  67
  68 void notify_other_processes(int signo) {
  69         int i = 0;
  70         struct queue_message msg;
  71         msg.signo[0] = signo;
  72
  73         for (; i < 3; i++) {
  74                 pid_t pid = processes->pids[i];
  75                 // Bleh
  76                 if (i != 1 && pid != 0) {
  77                         msg.mtype = i+1;
  78                         fprintf(stderr, "[%s] Sending message of type (%d) with value %d\n", "process1", msg.mtype, msg.signo[0]);
  79                         msgsnd(pid, &msg, sizeof(msg), 0);
  80                         fprintf(stderr, "[%s] Sending signal %s (%d) to PID: %d\n", "process2", strsignal(SIGUSR1), SIGUSR1, pid);
  81                         kill(pid, SIGUSR1);
  82                 }
  83         }
  84 }
  85
  86 /**
  87  * Handler for signals.
  88  */
  89 void sig_handler(int signo)
  90 {
  91         fprintf(stderr, "[%s] Received %s!\n", "process2", strsignal(signo));
  92         if (signo == SIGUSR1) {
  93                 fprintf(stderr, "[%s] > Notified!\n", "process2");
  94                 struct queue_message msg;
  95                 /* Check queues from both other processes */
  96                 if (msgrcv(processes->pids[0], &msg, sizeof(int), 2, 0) > 0) {
  97                         fprintf(stderr, "[%s] > Notified with value: %s!\n", "process2", strsignal(msg.signo[0]));
  98                         raise(msg.signo[0]);
  99                         break;
 100                 }
 101                 else if (msgrcv(processes->pids[2], &msg, sizeof(int), 2, 0) > 0) {
 102                         fprintf(stderr, "[%s] > Notified with value: %s!\n", "process2", strsignal(msg.signo[0]));
 103                         raise(msg.signo[0]);
 104                         break;
 105                 }
 106         }
 107         else if (signo == SIGTERM) {
 108                 fprintf(stderr, "[%s] > Signalling other processes..\n", "process2");
 109                 processes->pids[1] = 0;
 110                 notify_other_processes(signo);
 111
 112                 fprintf(stderr, "[%s] > Releasing resources\n", "process2");
 113                 close(read_descriptor);
 114                 close(write_descriptor);
 115                 unlink(write_descriptor);
 116                 exit(0);
 117         }
 118         else if (signo == SIGTSTP) {
 119                 fprintf(stderr, "[%s] > Close reading pipe\n", "process2");
 120                 close(read_descriptor);
 121                 notify_other_processes(signo);
 122                 fprintf(stderr, "[%s] > Close writing pipe\n", "process2");
 123                 close(write_descriptor);
 124                 raise (SIGSTOP);
 125         }
 126         else if (signo == SIGCONT) {
 127                 fprintf(stderr, "[%s] > Signalling other processes..\n", "process2");
 128                 notify_other_processes(signo);
 129
 130                 fprintf(stderr, "[%s] > Opening pipes\n", "process2");
 131                 write_descriptor = open(write_pipe, O_WRONLY);
 132                 read_descriptor = open(read_pipe, O_RDONLY);
 133         }
 134 }
 135
 136 /**
 137  * Program grabs data from process1, calculates number of characters in each line
 138  * and pass the value to process3.
 139  */
 140 int main(void) {
 141         /**
 142          * Buffer used for storing data from input pipe.
 143          * Data is stored in chunks of BUFFER_STEP size.
 144          * If data during reading is bigger than this value, then number of
 145          * characters is saved, and buffer is cleared for reading another chunk.
 146          */
 147         char buffer[BUFFER_STEP];
 148
 149         /** Index used when iterating buffer */
 150         int i = 0;
 151
 152         /** Stores number of bytes read from input pipe in current iteration */
 153         ssize_t count = 0;
 154
 155         int number_of_characters = 0;
 156
 157         fprintf(stderr, "[%s] Init!\n", "process2");
 158
 159         /**
 160          * Register signals handled by process
 161          */
 162         if (signal(SIGUSR1, sig_handler) == SIG_ERR) {
 163                 fprintf(stderr, "can't catch SIGUSR1\n");
 164         }
 165         if (signal(SIGTERM, sig_handler) == SIG_ERR) {
 166                 fprintf(stderr, "can't catch SIGTERM\n");
 167         }
 168         if (signal(SIGTSTP, sig_handler) == SIG_ERR) {
 169                 fprintf(stderr, "can't catch SIGTSTP\n");
 170         }
 171         if (signal(SIGCONT, sig_handler) == SIG_ERR) {
 172                 fprintf(stderr, "can't catch SIGCONT\n");
 173         }
 174
 175         /*
 176          * Register memory to share with other processes, and pass current
 177          * process id to the array.
 178          */
 179         shmid = shmget(shmkey, sizeof(struct message), 0666);
 180
 181         processes = (struct message *)shmat(shmid, NULL, 0);
 182         processes->pids[1] = getpid();
 183
 184         fprintf(stderr, "[%s] Shared pid: %d\n", "process2", getpid());
 185
 186         /**
 187          * Register message queue to communicate with other processes
 188          */
 189         qkey = getpid();
 190         qid_input = msgget(qkey, IPC_CREAT | 0666);
 191
 192         qid_output1 = msgget(processes->pids[1], IPC_CREAT | 0666);
 193         qid_output2 = msgget(processes->pids[2], IPC_CREAT | 0666);
 194
 195         /* Reading from process1 */
 196         read_descriptor = open(read_pipe, O_RDONLY);
 197
 198         /* Writing to process2 */
 199         mkfifo(write_pipe, 0666);
 200         write_descriptor = open(write_pipe, O_WRONLY);
 201
 202         while(1) {
 203                 /* Read data from input pipe */
 204                 count = read(read_descriptor, buffer, BUFFER_STEP);
 205
 206                 fprintf(stderr, "[%s] Fetched: %d bytes\n", "process2", count);
 207
 208                 if (count > 0) {
 209                         for (i = 0; i < count; i++, number_of_characters++) {
 210                                 if (buffer[i] == '\n') {
 211                                         fprintf(stderr, "[%s] Calculated: %d characters. Sending...\n", "process2", number_of_characters);
 212                                         write(write_descriptor, &number_of_characters, sizeof(number_of_characters));
 213                                         write(write_descriptor, '\n', 1);
 214                                         number_of_characters = 0;
 215                                 }
 216                         }
 217                 }
 218                 else {
 219                         break;
 220                 }
 221         }
 222
 223         /* Release resources in normal program flow exit. */
 224         close(read_descriptor);
 225         close(write_descriptor);
 226         unlink(write_descriptor);
 227
 228         return 0;
 229 }