(ITS#7564) LMDB library bug: reopening LMDB may fail, fixed-address mmap

[tamas.kenez@kishonti.net]

Full_Name: Tamás Kenéz
Version: LMDB 8eef7a42
OS: windows 7
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (82.141.191.242)


Using the LMDB library (commit 8eef7a4275eda) on windows 7:

To reproduce: Run mtest multiple times.
The test sometimes fails with the with the windows error code 487
(ERROR_INVALID_ADDRESS) in mdb_env_open -> mdb_env_open2 at this line

env->me_map = MapViewOfFileEx(mh, flags & MDB_WRITEMAP ?
			FILE_MAP_WRITE : FILE_MAP_READ,
			0, 0, env->me_mapsize, meta.mm_address);

The reason is that when windows fails to map at the specified address
(meta.mm_address) it returns 0.

I tried this quick workaround:

if ( !env->me_map )
    env->me_map = MapViewOfFileEx(mh, flags & MDB_WRITEMAP ?
			FILE_MAP_WRITE : FILE_MAP_READ,
			0, 0, env->me_mapsize, NULL);

which does return valid address, but then it fails later here:

    else if (meta.mm_address && env->me_map != meta.mm_address) {
		/* Can happen because the address argument to mmap() is just a
		 * hint.  mmap() can pick another, e.g. if the range is in use.
		 * The MAP_FIXED flag would prevent that, but then mmap could
		 * instead unmap existing pages to make room for the new map.
		 */
		return EBUSY;	/* TODO: Make a new MDB_* error code? */