c - Parent and child sync by signals trouble -


so, task sync parent , 2 children in way: 1 child sends sigusr2 signal parent , blocks waiting parent msg. sync implemented global flags, parent waits of flag_ch become 1 (it happens when child sends sigusr2) , sends signal sigusr1 child, , child resumes (cause global flag_p becomes 1)

the trouble parent receives signals 1 child, , blocks waiting second child signals, don't appear . idea?..

#include <stdlib.h> #include <stdio.h> #include <unistd.h> #include <signal.h> #include <sys/signalfd.h> #define lpc 10 pid_t ch[2];  sig_atomic_t flag_ch[2] = {0, 0}; sig_atomic_t flag_p = 0;  int get_ind(pid_t ch_pid) {     int i;     (i = 0; < 2; ++i) {         if (ch_pid == ch[i])             return i;     }     return -1; }  void usr_handler(int signo, siginfo_t* si, void* unused) {     int ch_index;     switch(signo) {         case sigusr2:             ch_index = get_ind(si->si_pid);             if (ch_index >= 0)                 flag_ch[ch_index] = 1;             else                 fprintf(stderr, "signal handled not child pid %d\n", si->si_pid);             break;         case sigusr1:             flag_p = 1;             break;     } }  void set_usr_handler(void) {     struct sigaction sa;     sa.sa_sigaction = usr_handler;     sa.sa_flags = sa_siginfo;     sa.sa_restorer = null;      sigemptyset(&sa.sa_mask);      if (0 != sigaction(sigusr1, &sa, null))         abort_prg("signal [sigusr1] error");      if (0 != sigaction(sigusr2, &sa, null))         abort_prg("signal [sigusr2] error"); }   void child_proc(void) {     int i;     (i = 0; < lpc; ++i) {         if (0 != kill(getppid(), sigusr2))             exit(1);         while (0 == flag_p) { };             flag_p = 0;     } }  int wait_child(void) {     while (0 == flag_ch[0] && 0 == flag_ch[1]) { };     if (1 == flag_ch[0]) {         flag_ch[0] = 0;         return ch[0];     }     flag_ch[1] = 0;     return ch[1]; }  void parent_proc(void) {     int i;     pid_t ch_pid;     (i = 0; < lpc * 2; ++i) {         ch_pid = wait_child();         printf("parent: received pid [%d]\n", ch_pid);         if (0 != kill(ch_pid, sigusr1))             exit(1);     } }  int main(int argc, char* argv[]) {     set_usr_handler();     int i;     (i = 0; < 2; ++i) {         pid_t child = fork();         if (0 > child)             exit(1);         if (0 == child) {             child_proc();             return 0;         }         ch[i] = child;     }        parent_proc();     return 0; }

my guess it's missing volatile in few global variable declarations. example, flag_p not being volatile means loop

while (flag_p == 0) { }

can run forever: gcc compiles load global variable once register, , loop until register non-zero (which never occurs).

a conservative approximation should make volatile mutable variables read or written in signal handler.

edit: source of problem can think of signals not cumulative: either parent process has no sigusr2 pending, or has one. if both children send parent process @ same time, 1 might delivered, far know.

edit: think "better" solution (more flexible , more portable) along lines of: not use signals @ all, use pipes. make 1 pipe between parent , each of children, , children send character 'x' on pipes when done. parent waits select(); or if wants wait until both children ready, can read 'x' character 1 pipe , other, blocking in both cases (the order doesn't matter).


Comments

Post a Comment

Popular posts from this blog

Why does Ruby on Rails generate add a blank line to the end of a file? -

running rails generate controller foo home results in: class foocontroller < application controller def home end end (there's nothing on line in actual file, blank line) is there purpose blank line? it's common use newline indicate end of line, last line. many editors (like vi, use) add in newline silently. consensus text files (especially in unix world) should end in newline, , there have been problems historically if wasn't present. why should text files end newline? the tool used count lines in file "wc" counts newlines in file, without trailing newline show 3 instead of 4. it improves readability of templates used in generator. consider: https://github.com/rails/rails/blob/master/railties/lib/rails/generators/rails/controller/templates/controller.rb to remove trailing newline, template have last line of: end<% end -%> instead of: end <% end -%> that seems less readable me. the discussion below refers
Read more

keyboard - Smiles and long press feature in Android -

i've created android keyboard. how add features inserting smilies, , using long keypresses display symbols? to create long-press behavior allows select several options pop-up menu, follow guide (specifically pop-up menu section): http://developer.android.com/guide/topics/ui/menus.html smileys (also known emoticons) combination of keys, understood programs , parsed same way. have do, when clicks smiley face on keyboard, simulate pressing of key combination matching emoticon. example, when clicks smiley, should simulate key presses ':' , ')' :). here's list of emoticons: http://en.wikipedia.org/wiki/list_of_emoticons
Read more

node.js - Bad Request - node js ajax post -

i'm using express 3.0 , node v0.11.0. have button submits form , i'm using ajax post data json object node server. client code is: $('#contact').submit(function(e) { console.log('submit called'); var formdata = json.stringify($('form').serializeobject()); console.log(formdata); $.ajax({ url: "http://localhost:3000/savedata/", type: "post", datatype: 'json', data: {objectdata: formdata}, contenttype: "application/json", complete: function() { console.log('process complete'); }, success: function(data) { console.log('process sucess'); }, error: function() { console.log('process error'); }, }); return false; }); then on server: var express = require('express'); var app = express(); app.set('views', __dirname + '/views'); app.set('view engine', 'jade'); app.use(express.bodyparser());
Read more