[FIX] Fix duplicate instance issue

diff --git a/daemon/main.c b/daemon/main.c
index fe32a3f..693c579 100644 (file)
--- a/daemon/main.c
+++ b/daemon/main.c
@@ -32,6 +32,7 @@
 #include <stdio.h>                     // for fopen, fprintf
 #include <stdlib.h>                    // for atexit
 #include <sys/types.h>         // for open
+#include <sys/file.h>
 #include <sys/stat.h>          // for open
 #include <sys/socket.h>                // for socket
 #include <sys/un.h>                    // for sockaddr_un
@@ -40,6 +41,7 @@
 #include <signal.h>                    // for signal
 #include <unistd.h>                    // for unlink
 #include <fcntl.h>                     // for open, fcntl
+#include <stdbool.h>
 #ifndef LOCALTEST
 #include <attr/xattr.h>                // for fsetxattr
 #endif
@@ -49,7 +51,7 @@
 #include "buffer.h"
 #include "debug.h"
 
-#define SINGLETON_LOCKFILE                     "/tmp/lockfile.da"
+#define SINGLETON_LOCKFILE                     "/tmp/da_manager.lock"
 #define PORTFILE                                       "/tmp/port.da"
 #define UDS_NAME                                       "/tmp/da.socket"
 
@@ -215,35 +217,30 @@ static int makeHostServerSocket()
 // initializing / finalizing functions
 // =============================================================================
 
-static int singleton(void)
+static bool ensure_singleton(const char *lockfile)
 {
-       struct flock fl;
-       int fd;
+       if (access(lockfile, F_OK) == 0)        /* File exists */
+               return false;
 
-       fd = open(SINGLETON_LOCKFILE, O_RDWR | O_CREAT, 0600);
-       if(fd < 0)
-       {
+       int lockfd = open(lockfile, O_WRONLY | O_CREAT, 0600);
+       if (lockfd < 0) {
                writeToPortfile(ERR_LOCKFILE_CREATE_FAILED);
                LOGE("singleton lock file creation failed");
-               return -1;
+               return false;
        }
+       /* To prevent race condition, also check for lock availiability. */
+       bool locked = flock(lockfd, LOCK_EX | LOCK_NB) == 0;
 
-       fl.l_start = 0;
-       fl.l_len = 0;
-       fl.l_type = F_WRLCK;
-       fl.l_whence = SEEK_SET;
-       if(fcntl(fd, F_SETLK, &fl) < 0)
-       {
+       if (!locked) {
                writeToPortfile(ERR_ALREADY_RUNNING);
                LOGE("another instance of daemon is already running");
-               close(fd);
-               return -1;
        }
-
-       close(fd);
-       return 0;
+       close(lockfd);
+       return locked;
 }
 
+
+
 // return 0 for normal case
 static int initializeManager()
 {
@@ -339,22 +336,19 @@ static int finalizeManager()
 // main function
 int main()
 {
-       int result;
+       if (!ensure_singleton(SINGLETON_LOCKFILE))
+               return 1;
+
        initialize_log();
 
        LOGI("da_started\n");
        atexit(_unlink_file);
 
        manager.portfile = fopen(PORTFILE, "w");
-       if(manager.portfile == NULL)
-       {
+       if (manager.portfile == NULL) {
                LOGE("cannot create portfile");
                return 1;
        }
-
-       if(singleton() < 0)
-               return 1;
-
        //for terminal exit
        signal(SIGHUP, SIG_IGN);
        chdir("/");
@@ -363,21 +357,17 @@ int main()
        setsid();
 
        // initialize manager
-       result = initializeManager();
+       int err = initializeManager();
        fclose(manager.portfile);
-       if(result == 0)
-       {
-               //daemon work
-               //FIX ME remove samplingThread it is only for debug
-               //samplingThread(NULL);
-               daemonLoop();
-               LOGI("daemon loop finished\n");
-               stop_all();
-               finalizeManager();
-               return 0;
-       }
-       else
-       {
+       if (err)
                return 1;
-       }
+
+       //daemon work
+       //FIX ME remove samplingThread it is only for debug
+       //samplingThread(NULL);
+       daemonLoop();
+       LOGI("daemon loop finished\n");
+       stop_all();
+       finalizeManager();
+       return 0;
 }