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
  58 /**
  59  * Unique key of message queue.
  60  */
  61 key_t qkey = 12356;
  62
  63 /**
  64  * Queue descriptor.
  65  */
  66 int qid;
  67
  68 /**
  69  * Structure holding queue message data.
  70  * Parameter mtype describes process to whom message is sent.
  71  * Parameter signo is a signal to raise after getting message.
  72  */
  73 struct queue_message {
  74         long mtype;
  75         int signo[1];
  76 };
  77
  78 void notify_other_processes(int signo) {
  79         int i = 0;
  80         struct queue_message msg;
  81         msg.signo[0] = signo;
  82
  83         for (; i < 3; i++) {
  84                 pid_t pid = processes->pids[i];
  85                 // Bleh
  86                 if (i != 1 && pid != 0) {
  87                         msg.mtype = i+1;
  88                         fprintf(stderr, "[%s] Sending message of type (%d) with value %d\n", "process1", msg.mtype, msg.signo[0]);
  89                         msgsnd(qid, &msg, sizeof(msg), 0);
  90                         fprintf(stderr, "[%s] Sending signal %s (%d) to PID: %d\n", "process2", strsignal(SIGUSR1), SIGUSR1, pid);
  91                         kill(pid, SIGUSR1);
  92                 }
  93         }
  94 }
  95
  96 /**
  97  * Handler for signals.
  98  */
  99 void sig_handler(int signo)
 100 {
 101         fprintf(stderr, "[%s] Received %s!\n", "process2", strsignal(signo));
 102         if (signo == SIGUSR1) {
 103                 fprintf(stderr, "[%s] > Notified!\n", "process2");
 104                 struct queue_message msg;
 105                 /* Check queues from both other processes */
 106                 if (msgrcv(qid, &msg, sizeof(int), 2, 0) > 0) {
 107                         fprintf(stderr, "[%s] > Notified with value: %s!\n", "process2", strsignal(msg.signo[0]));
 108                         raise(msg.signo[0]);
 109                 }
 110         }
 111         else if (signo == SIGTERM) {
 112                 fprintf(stderr, "[%s] > Signalling other processes..\n", "process2");
 113                 processes->pids[1] = 0;
 114                 notify_other_processes(signo);
 115
 116                 fprintf(stderr, "[%s] > Releasing resources\n", "process2");
 117                 close(read_descriptor);
 118                 close(write_descriptor);
 119                 unlink(write_descriptor);
 120                 exit(0);
 121         }
 122         else if (signo == SIGTSTP) {
 123                 fprintf(stderr, "[%s] > Close reading pipe\n", "process2");
 124                 close(read_descriptor);
 125                 processes->pids[1] = 0;
 126                 notify_other_processes(signo);
 127 //              sleep(1);
 128                 processes->pids[1] = getpid();
 129
 130                 fprintf(stderr, "[%s] > Close writing pipe\n", "process2");
 131                 close(write_descriptor);
 132                 raise (SIGSTOP);
 133         }
 134         else if (signo == SIGCONT) {
 135                 fprintf(stderr, "[%s] > Signalling other processes..\n", "process2");
 136                 processes->pids[1] = 0;
 137                 notify_other_processes(signo);
 138 //              sleep(1);
 139                 processes->pids[1] = getpid();
 140
 141                 fprintf(stderr, "[%s] > Opening pipes\n", "process2");
 142                 write_descriptor = open(write_pipe, O_WRONLY);
 143                 read_descriptor = open(read_pipe, O_RDONLY);
 144         }
 145 }
 146
 147 /**
 148  * Program grabs data from process1, calculates number of characters in each line
 149  * and pass the value to process3.
 150  */
 151 int main(void) {
 152         /**
 153          * Buffer used for storing data from input pipe.
 154          * Data is stored in chunks of BUFFER_STEP size.
 155          * If data during reading is bigger than this value, then number of
 156          * characters is saved, and buffer is cleared for reading another chunk.
 157          */
 158         char buffer[BUFFER_STEP];
 159
 160         /** Index used when iterating buffer */
 161         int i = 0;
 162
 163         /** Stores number of bytes read from input pipe in current iteration */
 164         ssize_t count = 0;
 165
 166         int number_of_characters = 0;
 167
 168         fprintf(stderr, "[%s] Init!\n", "process2");
 169
 170         /**
 171          * Register signals handled by process
 172          */
 173         if (signal(SIGUSR1, sig_handler) == SIG_ERR) {
 174                 fprintf(stderr, "can't catch SIGUSR1\n");
 175         }
 176         if (signal(SIGTERM, sig_handler) == SIG_ERR) {
 177                 fprintf(stderr, "can't catch SIGTERM\n");
 178         }
 179         if (signal(SIGTSTP, sig_handler) == SIG_ERR) {
 180                 fprintf(stderr, "can't catch SIGTSTP\n");
 181         }
 182         if (signal(SIGCONT, sig_handler) == SIG_ERR) {
 183                 fprintf(stderr, "can't catch SIGCONT\n");
 184         }
 185
 186         /*
 187          * Register memory to share with other processes, and pass current
 188          * process id to the array.
 189          */
 190         shmid = shmget(shmkey, sizeof(struct message), 0666);
 191
 192         processes = (struct message *)shmat(shmid, NULL, 0);
 193         processes->pids[1] = getpid();
 194
 195         fprintf(stderr, "[%s] Shared pid: %d\n", "process2", getpid());
 196
 197         /**
 198          * Register message queue to communicate with other processes
 199          */
 200         qid = msgget(qkey, 0666);
 201
 202         /* Reading from process1 */
 203         read_descriptor = open(read_pipe, O_RDONLY);
 204
 205         /* Writing to process2 */
 206         mkfifo(write_pipe, 0666);
 207         write_descriptor = open(write_pipe, O_WRONLY);
 208
 209         while(1) {
 210                 /* Read data from input pipe */
 211                 count = read(read_descriptor, buffer, BUFFER_STEP);
 212
 213                 fprintf(stderr, "[%s] Fetched: %d bytes\n", "process2", count);
 214
 215                 if (count > 0) {
 216                         for (i = 0; i < count; i++, number_of_characters++) {
 217                                 if (buffer[i] == '\n') {
 218                                         fprintf(stderr, "[%s] Calculated: %d characters. Sending...\n", "process2", number_of_characters);
 219                                         write(write_descriptor, &number_of_characters, sizeof(number_of_characters));
 220                                         write(write_descriptor, '\n', 1);
 221                                         number_of_characters = 0;
 222                                 }
 223                         }
 224                 }
 225                 else {
 226                         break;
 227                 }
 228         }
 229
 230         /* Release resources in normal program flow exit. */
 231         close(read_descriptor);
 232         close(write_descriptor);
 233         unlink(write_descriptor);
 234
 235         return 0;
 236 }