Changeset 895 for trunk/server/lib/tdb/common/io.c

Timestamp:

Mar 18, 2016, 7:53:30 PM (9 years ago)

Author:

Silvan Scherrer

Message:

tdb: Use DosSetFileLocks directly for db locks.

This is to overcome some fcntl() API incompleteness in kLIBC
(like inability to upgrade locks or join adjacent lock regions
into one). It made the torture test run a bit better but there
are still two major problems both coming from DosSetFileLocks
impl (which fcntl() is currently based upon too): a) inability to
detect deadlocks and b) missing atomic unlock/lock support if
unlock/lock regions don't match.

With the current implementation, tdborture works fine for 1 or 2
worker processes but hangs when there are 3 or more. [Before that,
it would only work with 1 process and would likely to corrupt
the database and terminate if there were 2 or more processes].

Author: Dmitriy Kuminov (@dmik).

File:

• trunk/server/lib/tdb/common/io.c (modified) (2 diffs)

trunk/server/lib/tdb/common/io.c

@@ -91 +91 @@
                 return -1;
 
-#ifdef __OS2__
-        // YD we must upgrade read locks to write locks (exclusive), as otherwise
-        // the owner (us) is not allowed to write to the file (different from unix)
-        // if a wider previous lock is in effect, we cannot write lock our segment
-        // (e.g. a lock_upgrade locks all the file), so we hope the previous lock 
-        // is a write lock: do not wait for lock.
-        // so this is what we try here:
-        // 1. add a write lock and see it it works
-        // 2. if the write lock wasn't set, we try to unlock the segment
-        //    first and add the write lock afterwards
-        // 3. we remove the write lock further down 
-        // 4. we add the removed lock from step #2 again 
-        int upgradeLockRC = 0;
-        int unlockRC = -1;
-        upgradeLockRC = tdb_brlock(tdb, F_WRLCK, off, len, TDB_LOCK_NOWAIT);
-        if (upgradeLockRC != 0) {
-                unlockRC = tdb_brunlock(tdb, F_RDLCK, off, 1);
-                upgradeLockRC = tdb_brlock(tdb, F_WRLCK, off, len, TDB_LOCK_NOWAIT);
-        }
-        // no need to log a successful upgrade
-        if (upgradeLockRC != 0)
-        TDB_LOG((tdb, TDB_DEBUG_TRACE,"upgrading lock at %d len=%d "
-                "before writing %s (rc=%d).\n", off, len,
-                 upgradeLockRC ? "failed":"was successful", upgradeLockRC));
-#endif
         if (tdb->map_ptr) {
                 memcpy(off + (char *)tdb->map_ptr, buf, len);
@@ -141 +116 @@
                                  "write %d bytes at %d in two attempts\n",
                                  len, off));
-#ifdef __OS2__ // remove our lock, if upgrade succeded
-                        if (upgradeLockRC == 0)
-                                tdb_brunlock( tdb, F_WRLCK, off, len);
-                        if (unlockRC == 0)
-                                tdb_brlock( tdb, F_RDLCK, off, 1, TDB_LOCK_WAIT);
-#endif
-                        return -1;
-                }
-        }
-#ifdef __OS2__ // remove our lock, if upgrade succeded
-        if (upgradeLockRC == 0)
-                tdb_brunlock( tdb, F_WRLCK, off, len);
-        if (unlockRC == 0)
-                tdb_brlock( tdb, F_RDLCK, off, 1, TDB_LOCK_WAIT);
-#endif
+                        return -1;
+                }
+        }
         return 0;
 }