syncdaemon: change pidfile handling approach

Signal handling of the python interpreter is a bit messy, so we cannot
rely on executing a final clause upon termination. Switch over fcntl
lock based pidfile handling which can provide reliable info about status
of the process. (Due to aforementioned reason, pidfile as such is not
guaranteed to be cleaned up, but lock acquisition is a reliable measure.)

Signed-off-by: Csaba Henk <csaba@gluster.com>
Signed-off-by: Anand V. Avati <avati@dev.gluster.com>

BUG: 1570 (geosync related changes)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=1570

1 files changed, 46 insertions, 27 deletions

diff --git a/xlators/features/marker/utils/syncdaemon/gsyncd.py b/xlators/features/marker/utils/syncdaemon/gsyncd.py
index 8a91c5ef9..b8b92056b 100644
--- a/xlators/features/marker/utils/syncdaemon/gsyncd.py
+++ b/xlators/features/marker/utils/syncdaemon/gsyncd.py
@@ -9,9 +9,10 @@ import signal
 import select
 import shutil
 import optparse
+import fcntl
 from optparse import OptionParser, SUPPRESS_HELP
 from logging import Logger
-from errno import EEXIST, ENOENT
+from errno import EEXIST, ENOENT, EACCES, EAGAIN
 
 from gconf import gconf
 from configinterface import GConffile
@@ -53,26 +54,42 @@ class GLogger(Logger):
         logging.basicConfig(**lprm)
 
 
-def startup(**kw):
-    def write_pid(fn):
-        fd = None
+def grabfile(fname, content=None):
+    # damn those messy open() mode codes
+    fd = os.open(fname, os.O_CREAT|os.O_RDWR)
+    f = os.fdopen(fd, 'r+b', 0)
+    try:
+        fcntl.lockf(f, fcntl.LOCK_EX|fcntl.LOCK_NB)
+    except:
+        ex = sys.exc_info()[1]
+        f.close()
+        if isinstance(ex, IOError) and ex.errno in (EACCES, EAGAIN):
+            # cannot grab, it's taken
+            return
+        raise
+    if content:
         try:
-            fd = os.open(fn, os.O_CREAT|os.O_TRUNC|os.O_WRONLY|os.O_EXCL)
-            os.write(fd, str(os.getpid()) + '\n')
-        finally:
-            if fd:
-                os.close(fd)
+            f.truncate()
+            f.write(content)
+        except:
+            f.close()
+            raise
+    gconf.permanent_handles.append(f)
+    return f
+
+def grabpidfile(fname=None, setpid=True):
+    if not fname:
+        fname = gconf.pid_file
+    content = None
+    if setpid:
+        content = str(os.getpid()) + '\n'
+    return grabfile(fname, content=content)
 
+def startup(**kw):
     if getattr(gconf, 'pid_file', None) and kw.get('go_daemon') != 'postconn':
-        try:
-            write_pid(gconf.pid_file)
-        except OSError:
-            gconf.pid_file = None
-            ex = sys.exc_info()[1]
-            if ex.errno == EEXIST:
-                sys.stderr.write("pidfile is taken, exiting.\n")
-                exit(2)
-            raise
+        if not grabpidfile():
+            sys.stderr.write("pidfile is taken, exiting.\n")
+            exit(2)
 
     if kw.get('go_daemon') == 'should':
         x, y = os.pipe()
@@ -86,7 +103,8 @@ def startup(**kw):
         for f in (sys.stdin, sys.stdout, sys.stderr):
             os.dup2(dn, f.fileno())
         if getattr(gconf, 'pid_file', None):
-            write_pid(gconf.pid_file + '.tmp')
+            if not grabpidfile(gconf.pid_file + '.tmp'):
+                raise RuntimeError("cannot grap temporary pidfile")
             os.rename(gconf.pid_file + '.tmp', gconf.pid_file)
         # wait for parent to terminate
         # so we can start up with
@@ -102,20 +120,21 @@ def startup(**kw):
 
 def finalize(*a):
     if getattr(gconf, 'pid_file', None):
+        rm_pidf = True
         if gconf.cpid:
+            # exit path from parent branch of daemonization
+            rm_pidf = False
             while True:
-                f = open(gconf.pid_file)
-                pid = f.read()
-                f.close()
-                pid = int(pid.strip())
-                if pid == gconf.cpid:
+                f = grabpidfile(setpid=False)
+                if not f:
+                    # child has already taken over pidfile
                     break
-                if pid != os.getpid():
-                    raise RuntimeError("corrupt pidfile")
                 if os.waitpid(gconf.cpid, os.WNOHANG)[0] == gconf.cpid:
+                    # child has terminated
+                    rm_pidf = True
                     break;
                 time.sleep(0.1)
-        else:
+        if rm_pidf:
             try:
                 os.unlink(gconf.pid_file)
             except: