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POWhy can I not get system V message queues working with fork()?
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copied!<p>I have a program here: </p> <pre><code>#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/ipc.h> #include <sys/types.h> #include <sys/msg.h> #include <sys/wait.h> #include <errno.h> #include "linkedlist.h" #include "globals.h" #include "card.h" #include "logging.h" #include "stack.h" #include "servers.h" #include "player.h" #define VERSION "0.1" #define ERR -1 /* * Main function runs, loads 5 named table objects. For each table * created a fork is created for that specific table object that * allows each table to run independently. * * Usernames details are also created and prepared. These are hardcoded * until I add database logic later. * * After the tables are prepared, the main function starts a server * listening thread that waits for UNIX sockets to connect to it. When * they arrive it spawns a handling thread that does a quick login check * and then asks the user which of the named tables they want to play on * * The socket information is then connected to the table, so the table can * then communicate with user. When the table is full, the table algorithm * is responcible for basically looping contineously, creating new "games" * until only one player is left. He is the winner. When he wins, the table * exits. * * the game loop does all the real work for the texas holdem game, hosting * rounds of bets, dealing cards etc. */ void table_process(int tables_id); void main_game_loop(void); int main(int argc, char **argv) { int main_process_id; int connection_process_id; char table_config_name[8]; char *table_name; stack *my_deck; card *current_card; int i; int s; printf("------------ PRT POKER -----------\nA texas holdem poker server\n~~~~Version: %s~~~~~~~\n", VERSION); config_load("poker.conf"); logging_init(); if (key = ftok("/mnt/mydocuments/git/texas_holdem/poker", 'a') == -1) { logging_critical("Call to ftok failed"); exit(1); } // if ((msg_queue = msgget(key, 0644 | IPC_CREAT)) == -1) // { // logging_critical("call to msgget failed"); // exit(1); // } //read int the list of tables from the configuration file config_get_int("players_per_table", &player_count); logging_info("players per table: %i", *player_count); config_get_int("table_count", &table_count); logging_info("number of tables: %i", *table_count); table_names = malloc(sizeof(char*) * (*table_count)); logging_info("Table count: %d", *table_count); for (i = 0; i < *table_count; i++) { sprintf(table_config_name, "table_%d", (i + 1)); config_get_string(table_config_name, &table_name); table_names[i] = table_name; logging_info("Created table %d: %s", i, table_name); if (fork() == 0) { table_process(i); _exit(0); } } main_process_id = getpid(); connection_process_id = fork(); logging_info("connecton process: %d", connection_process_id); if (connection_process_id == 0) { wait_for_players(); _exit(0); } else waitpid(connection_process_id, &s, 0); logging_info("Application ended"); return 0; } void table_process(int table_id) { linkedlist *players; player *p; int players_added; if ((msg_queue = msgget(key, 0644 | IPC_CREAT)) == -1) { logging_critical("call to msgget failed"); exit(1); } logging_info("table %s (%i) running in process %d", table_names[table_id], table_id, getpid()); players = linkedlist_new(); players_added = *player_count; while (players_added > 0) { logging_info("still waiting for %i players to join %s with queue id %i", players_added, table_names[table_id], table_id + MSG_QUEUE_OFFSET); //THIS DOESN'T WORK!!!! IT DOESN'T WAKE UP if (msgrcv(msg_queue, &p, sizeof(player), table_id + MSG_QUEUE_OFFSET, 0) == -1) { logging_critical("recieving from message queue failed"); _exit(1); } else logging_info("played joined %s", table_names[table_id]); logging_debug("player = %s, %s", p->name, p->password); players_added--; } logging_info("table %s ready to start!!!!!", table_names[table_id]); } void main_game_loop(void) { logging_debug("main_game_loop"); } </code></pre> <p>The program is supposed to start and fork into 4 threads. The first three threads call msgget() to create a system V message queue.</p> <p>Then they all call msgrcv() and wait for a different id to occur.</p> <p>The fourth thread listens for connecting clients and then invokes msgsnd(). For some reason, none of the forks waiting for a message awake again.</p> <ol> <li><p>I'm sure the message queue is correct. </p></li> <li><p>I have a print statement before msgsrcv so I can see that see that the fork happens correctly for each statement. There is also a print statement afterwards so I can see the code doesn't pass it.</p></li> <li><p>I have run ipcs from the command prompt.</p></li> <li><p>There is definitely a message queue created and definetly has a message in it.</p></li> <li><p>If I change the msgrcv to say "0" then one of the threads will wake up but that's not the behaviour I want.</p></li> <li><p>msgget() doesn't throw an error. </p></li> <li><p>msgsnd() didn't throw an error.</p></li> <li><p>I'm positive the id in the structure is correct.</p></li> </ol> <p>Any ideas what I am doing wrong?</p>

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