Changeset 4644

Timestamp:

10/01/06 22:07:18 (2 years ago)

Author:

erijo

Message:

Redo the "only one instance of Licq" logic.

Instead of checking if the pid in licq.pid is running, use advisory locking. First we grab a write lock on licq.pid. If it fails, this means that licq is already running, otherwise we're alone. By never closing the file, we keep the lock until licq is killed (normally or abnormally) when the kernel will close all open files and remove all locks.

Fixes #1353.

Location:

trunk/licq/src

Files:

• licq.cpp (modified) (5 diffs)
• licq.h (modified) (1 diff)

trunk/licq/src/licq.cpp

@@ -149 +149 @@
 /*-----End of OpenSSL code-------------------------------------------------*/
 
+/**
+ * Prints the @a error to stderr (by means of gLog), and if the user is running
+ * X, tries to show a dialog with the error.
+ */
+static void DisplayFatalError(const char* error)
+{
+  gLog.Error(error);
+
+  // Try to show the error if we're running X
+  if (getenv("DISPLAY") != NULL)
+  {
+    pid_t child = fork();
+    if (child == 0)
+    {
+      // execlp never returns (except on error).
+      execlp("kdialog", "kdialog", "--error", error, NULL);
+      execlp("Xdialog", "Xdialog", "--title", "Error", "--msgbox", error, "0", "0", NULL);
+      execlp("xmessage", "xmessage", "-center", error, NULL);
+
+      exit(EXIT_FAILURE);
+    }
+    else if (child != -1)
+    {
+      int status;
+      waitpid(child, &status, 0);
+    }
+  }
+}
 
 /*-----Helper functions for CLicq::UpgradeLicq-----------------------------*/
@@ -180 +208 @@
   pthread_mutex_init(&mutex_plugins, NULL);
   pthread_mutex_init(&mutex_protoplugins, NULL);
-  m_bDeletePID = true;
 
   //FIXME ICQ should be put into its own plugin.
@@ -307 +334 @@
 
   // Check pid
+  // We do this by acquiring a write lock on the pid file and never closing the file.
+  // When Licq is killed (normally or abnormally) the file will be closed by the operating
+  // system and the lock released.
   char szConf[MAX_FILENAME_LEN], szKey[32];
   snprintf(szConf, MAX_FILENAME_LEN, "%s/licq.pid", BASE_DIR);
   szConf[MAX_FILENAME_LEN - 1] = '\0';
-  FILE *fs = fopen(szConf, "r");
-  if (fs != NULL)
-  {
-    fgets(szKey, 32, fs);
-    pid_t pid = atol(szKey);
-    if (pid != 0)
-    {
-      if (kill(pid, 0) == -1) {
-        gLog.Warn(tr("%sLicq: Ignoring stale lockfile (pid %d)\n"), L_WARNxSTR, pid);
+
+  // Never close pidFile!
+  int pidFile = open(szConf, O_RDWR | O_CREAT);
+  if (pidFile < 0)
+  {
+    // We couldn't open (or create) the file for writing.
+    // If the file doesn't exists we continue without lockfile protection.
+    // If it does exist, we bail out.
+    struct stat buf;
+    if (stat(szConf, &buf) < 0 && errno == ENOENT)
+    {
+      gLog.Warn(tr("%sLicq: %s cannot be opened for writing.\n"
+                   "%s      skipping lockfile protection.\n"),
+                L_WARNxSTR, szConf, L_BLANKxSTR);
+    }
+    else
+    {
+      const size_t ERR_SIZE = 511;
+      char error[ERR_SIZE + 1];
+
+      // Try to read the pid of running Licq instance.
+      FILE* fs = fopen(szConf, "r");
+      if (fs != NULL)
+      {
+          fgets(szKey, 32, fs);
+          pid_t pid = atol(szKey);
+
+          snprintf(error, ERR_SIZE,
+                   tr("%sLicq: Already running at pid %d.\n"
+                      "%s      Kill process or remove %s.\n"),
+                   L_ERRORxSTR, pid, L_BLANKxSTR, szConf);
+          fclose(fs);
       }
       else
       {
-        const size_t ERR_SIZE = 511;
-        char error[ERR_SIZE + 1];
         snprintf(error, ERR_SIZE,
-            tr("%sLicq: Already running at pid %d.\n"
-               "%s      Kill process or remove %s.\n"),
-            L_ERRORxSTR, pid, L_BLANKxSTR, szConf);
-        error[ERR_SIZE] = '\0';
-
-        gLog.Error(error);
-        m_bDeletePID = false;
-
-        // Try to show the error if we're running X
-        if (getenv("DISPLAY") != NULL)
-        {
-          pid_t child = fork();
-          if (child == 0)
-          {
-            // execlp never returns (except on error).
-            execlp("kdialog", "kdialog", "--error", error, NULL);
-            execlp("Xdialog", "Xdialog", "--title", "Error", "--msgbox", error, "0", "0", NULL);
-            execlp("xmessage", "xmessage", "-center", error, NULL);
-
-            exit(EXIT_FAILURE);
-          }
-          else if (child != -1)
-          {
-            int status;
-            waitpid(child, &status, 0);
-          }
-        }
-
-        return false;
+                 tr("%sLicq: Unabled to determine pid of running Licq instance.\n"),
+                 L_ERRORxSTR);
       }
-    }
-    fclose(fs);
-  }
-  fs = fopen(szConf, "w");
-  if (fs != NULL)
-  {
-    chmod(szConf, 00600);
-    fprintf(fs, "%d\n", getpid());
-    fclose(fs);
+
+      error[ERR_SIZE] = '\0';
+      DisplayFatalError(error);
+
+      return false;
+    }
   }
   else
-    gLog.Warn(tr("%sLicq: %s cannot be opened for writing.\n"
-                 "%s      skipping lockfile protection.\n"),
-              L_WARNxSTR, szConf, L_BLANKxSTR);
+  {
+    struct flock lock;
+    lock.l_type = F_WRLCK; // Write lock is exclusive lock
+    lock.l_whence = SEEK_SET;
+    lock.l_start = 0;
+    lock.l_len = 0; // Lock file through to the end of file
+
+    if (fcntl(pidFile, F_SETLK, &lock) != 0)
+    {
+      // Failed to get the lock => Licq is already running
+      const size_t ERR_SIZE = 511;
+      char error[ERR_SIZE + 1];
+
+      if (fcntl(pidFile, F_GETLK, &lock) != 0)
+      {
+        snprintf(error, ERR_SIZE,
+                tr("%sLicq: Unabled to determine pid of running Licq instance.\n"),
+                L_ERRORxSTR);
+      }
+      else
+      {
+        snprintf(error, ERR_SIZE,
+                tr("%sLicq: Already running at pid %d.\n"),
+                L_ERRORxSTR, lock.l_pid);
+      }
+
+      error[ERR_SIZE] = '\0';
+      DisplayFatalError(error);
+
+      return false;
+    }
+    else
+    {
+      // Save our pid in the file
+      ftruncate(pidFile, 0);
+      int size = snprintf(szKey, 32, "%d\n", getpid());
+      write(pidFile, szKey, (size > 32 ? 32 : size));
+    }
+  }
 
   // Open the config file
@@ -502 +559 @@
   // Kill the daemon
   if (licqDaemon != NULL) delete licqDaemon;
-
-  // Remove the lock file
-  if (m_bDeletePID)
-  {
-    char szConf[MAX_FILENAME_LEN];
-    snprintf(szConf, MAX_FILENAME_LEN, "%s/licq.pid", BASE_DIR);
-    remove(szConf);
-  }
 }
 
@@ -1174 +1223 @@
   pthread_join(*t, NULL);
 
-  // Remove the pid flag
-  char sz[MAX_FILENAME_LEN];
-  snprintf(sz, MAX_FILENAME_LEN, "%s/licq.pid", BASE_DIR);
-  sz[MAX_FILENAME_LEN - 1] = '\0';
-  remove(sz);
-
   return list_plugins.size();
 }

trunk/licq/src/licq.h

@@ -46 +46 @@
   ProtoPluginsList list_protoplugins;
   pthread_mutex_t mutex_protoplugins;
-  bool m_bDeletePID;
 
 friend class CICQDaemon;