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 = 12356;
  58 int qid;
  59
  60 struct queue_message {
  61         long mtype;
  62         int signo[1];
  63 };
  64
  65 void notify_other_processes(int signo) {
  66         int i = 0;
  67         struct queue_message msg;
  68         msg.signo[0] = signo;
  69
  70         for (; i < 3; i++) {
  71                 pid_t pid = processes->pids[i];
  72                 // Bleh
  73                 if (i != 1 && pid != 0) {
  74                         msg.mtype = i+1;
  75                         fprintf(stderr, "[%s] Sending message of type (%d) with value %d\n", "process1", msg.mtype, msg.signo[0]);
  76                         msgsnd(qid, &msg, sizeof(msg), 0);
  77                         fprintf(stderr, "[%s] Sending signal %s (%d) to PID: %d\n", "process2", strsignal(SIGUSR1), SIGUSR1, pid);
  78                         kill(pid, SIGUSR1);
  79                 }
  80         }
  81 }
  82
  83 /**
  84  * Handler for signals.
  85  */
  86 void sig_handler(int signo)
  87 {
  88         fprintf(stderr, "[%s] Received %s!\n", "process2", strsignal(signo));
  89         if (signo == SIGUSR1) {
  90                 fprintf(stderr, "[%s] > Notified!\n", "process2");
  91                 struct queue_message msg;
  92                 /* Check queues from both other processes */
  93                 if (msgrcv(qid, &msg, sizeof(int), 2, 0) > 0) {
  94                         fprintf(stderr, "[%s] > Notified with value: %s!\n", "process2", strsignal(msg.signo[0]));
  95                         raise(msg.signo[0]);
  96                 }
  97                 else if (msgrcv(qid, &msg, sizeof(int), 2, 0) > 0) {
  98                         fprintf(stderr, "[%s] > Notified with value: %s!\n", "process2", strsignal(msg.signo[0]));
  99                         raise(msg.signo[0]);
 100                 }
 101         }
 102         else if (signo == SIGTERM) {
 103                 fprintf(stderr, "[%s] > Signalling other processes..\n", "process2");
 104                 processes->pids[1] = 0;
 105                 notify_other_processes(signo);
 106
 107                 fprintf(stderr, "[%s] > Releasing resources\n", "process2");
 108                 close(read_descriptor);
 109                 close(write_descriptor);
 110                 unlink(write_descriptor);
 111                 exit(0);
 112         }
 113         else if (signo == SIGTSTP) {
 114                 fprintf(stderr, "[%s] > Close reading pipe\n", "process2");
 115                 close(read_descriptor);
 116                 notify_other_processes(signo);
 117                 fprintf(stderr, "[%s] > Close writing pipe\n", "process2");
 118                 close(write_descriptor);
 119                 raise (SIGSTOP);
 120         }
 121         else if (signo == SIGCONT) {
 122                 fprintf(stderr, "[%s] > Signalling other processes..\n", "process2");
 123                 notify_other_processes(signo);
 124
 125                 fprintf(stderr, "[%s] > Opening pipes\n", "process2");
 126                 write_descriptor = open(write_pipe, O_WRONLY);
 127                 read_descriptor = open(read_pipe, O_RDONLY);
 128         }
 129 }
 130
 131 /**
 132  * Program grabs data from process1, calculates number of characters in each line
 133  * and pass the value to process3.
 134  */
 135 int main(void) {
 136         /**
 137          * Buffer used for storing data from input pipe.
 138          * Data is stored in chunks of BUFFER_STEP size.
 139          * If data during reading is bigger than this value, then number of
 140          * characters is saved, and buffer is cleared for reading another chunk.
 141          */
 142         char buffer[BUFFER_STEP];
 143
 144         /** Index used when iterating buffer */
 145         int i = 0;
 146
 147         /** Stores number of bytes read from input pipe in current iteration */
 148         ssize_t count = 0;
 149
 150         int number_of_characters = 0;
 151
 152         fprintf(stderr, "[%s] Init!\n", "process2");
 153
 154         /**
 155          * Register signals handled by process
 156          */
 157         if (signal(SIGUSR1, sig_handler) == SIG_ERR) {
 158                 fprintf(stderr, "can't catch SIGUSR1\n");
 159         }
 160         if (signal(SIGTERM, sig_handler) == SIG_ERR) {
 161                 fprintf(stderr, "can't catch SIGTERM\n");
 162         }
 163         if (signal(SIGTSTP, sig_handler) == SIG_ERR) {
 164                 fprintf(stderr, "can't catch SIGTSTP\n");
 165         }
 166         if (signal(SIGCONT, sig_handler) == SIG_ERR) {
 167                 fprintf(stderr, "can't catch SIGCONT\n");
 168         }
 169
 170         /*
 171          * Register memory to share with other processes, and pass current
 172          * process id to the array.
 173          */
 174         shmid = shmget(shmkey, sizeof(struct message), 0666);
 175
 176         processes = (struct message *)shmat(shmid, NULL, 0);
 177         processes->pids[1] = getpid();
 178
 179         fprintf(stderr, "[%s] Shared pid: %d\n", "process2", getpid());
 180
 181         /**
 182          * Register message queue to communicate with other processes
 183          */
 184         qid = msgget(qkey, 0666);
 185
 186         /* Reading from process1 */
 187         read_descriptor = open(read_pipe, O_RDONLY);
 188
 189         /* Writing to process2 */
 190         mkfifo(write_pipe, 0666);
 191         write_descriptor = open(write_pipe, O_WRONLY);
 192
 193         while(1) {
 194                 /* Read data from input pipe */
 195                 count = read(read_descriptor, buffer, BUFFER_STEP);
 196
 197                 fprintf(stderr, "[%s] Fetched: %d bytes\n", "process2", count);
 198
 199                 if (count > 0) {
 200                         for (i = 0; i < count; i++, number_of_characters++) {
 201                                 if (buffer[i] == '\n') {
 202                                         fprintf(stderr, "[%s] Calculated: %d characters. Sending...\n", "process2", number_of_characters);
 203                                         write(write_descriptor, &number_of_characters, sizeof(number_of_characters));
 204                                         write(write_descriptor, '\n', 1);
 205                                         number_of_characters = 0;
 206                                 }
 207                         }
 208                 }
 209                 else {
 210                         break;
 211                 }
 212         }
 213
 214         /* Release resources in normal program flow exit. */
 215         close(read_descriptor);
 216         close(write_descriptor);
 217         unlink(write_descriptor);
 218
 219         return 0;
 220 }