1 files changed, 49 insertions, 8 deletions

diff --git a/lib/logger.rb b/lib/logger.rb
index f24b20b1a6..2eb4e642d2 100644
--- a/lib/logger.rb
+++ b/lib/logger.rb
@@ -588,24 +588,32 @@ private
   private
 
     def open_logfile(filename)
-      if (FileTest.exist?(filename))
+      begin
         open(filename, (File::WRONLY | File::APPEND))
-      else
+      rescue Errno::ENOENT
         create_logfile(filename)
       end
     end
 
     def create_logfile(filename)
-      logdev = open(filename, (File::WRONLY | File::APPEND | File::CREAT))
-      logdev.sync = true
-      add_log_header(logdev)
+      begin
+        logdev = open(filename, (File::WRONLY | File::APPEND | File::CREAT | File::EXCL))
+        logdev.flock(File::LOCK_EX)
+        logdev.sync = true
+        add_log_header(logdev)
+        logdev.flock(File::LOCK_UN)
+      rescue Errno::EEXIST
+        # file is created by another process
+        logdev = open_logfile(filename)
+        logdev.sync = true
+      end
       logdev
     end
 
     def add_log_header(file)
       file.write(
         "# Logfile created on %s by %s\n" % [Time.now.to_s, Logger::ProgName]
-      )
+      ) if file.size == 0
     end
 
     SiD = 24 * 60 * 60
@@ -614,17 +622,50 @@ private
       if @shift_age.is_a?(Integer)
         # Note: always returns false if '0'.
         if @filename && (@shift_age > 0) && (@dev.stat.size > @shift_size)
-          shift_log_age
+          lock_shift_log { shift_log_age }
         end
       else
         now = Time.now
         period_end = previous_period_end(now)
         if @dev.stat.mtime <= period_end
-          shift_log_period(period_end)
+          lock_shift_log { shift_log_period(period_end) }
         end
       end
     end
 
+    def lock_shift_log
+      begin
+        retry_limit = 8
+        retry_sleep = 0.1
+        begin
+          File.open(@filename, File::WRONLY | File::APPEND) do |lock|
+            lock.flock(File::LOCK_EX) # inter-process locking. will be unlocked at closing file
+            ino = lock.stat.ino
+            if ino == File.stat(@filename).ino
+              yield # log shifting
+            else
+              # log shifted by another process (i-node before locking and i-node after locking are different)
+              @dev.close rescue nil
+              @dev = open_logfile(@filename)
+              @dev.sync = true
+            end
+          end
+        rescue Errno::ENOENT
+          # @filename file would not exist right after #rename and before #create_logfile
+          if retry_limit <= 0
+            warn("log rotation inter-process lock failed. #{$!}")
+          else
+            sleep retry_sleep
+            retry_limit -= 1
+            retry_sleep *= 2
+            retry
+          end
+        end
+      rescue
+        warn("log rotation inter-process lock failed. #{$!}")
+      end
+    end
+
     def shift_log_age
       (@shift_age-3).downto(0) do |i|
         if FileTest.exist?("#{@filename}.#{i}")