5.5/sql/handler.cc:5107: int handler::ha_external_lock(THD*, int): Assertion `next_insert_id == 0' failed.
151002 21:20:47 [ERROR] mysqld got signal 6 ;

#6  0x00007f3390ef7311 in *__GI___assert_fail (assertion=0xe0ef02 "next_insert_id == 0", file=<optimized out>, line=5107, function=0xe0fb00 "int handler::ha_external_lock(THD*, int)") at assert.c:81
#7  0x00000000007f3a46 in handler::ha_external_lock (this=0x7f337cd1a878, thd=0x7f337ccb4080, lock_type=2) at 5.5/sql/handler.cc:5107
#8  0x00000000008c0f44 in unlock_external (thd=0x7f337ccb4080, table=0x7f337449b328, count=1) at 5.5/sql/lock.cc:673
#9  0x00000000008c04a2 in mysql_unlock_tables (thd=0x7f337ccb4080, sql_lock=0x7f337449b300, free_lock=true) at 5.5/sql/lock.cc:384
#10 0x00000000005d576a in close_thread_tables (thd=0x7f337ccb4080) at 5.5/sql/sql_base.cc:1580
#11 0x000000000061ddef in handle_delayed_insert (arg=0x7f337ccb4060) at 5.5/sql/sql_insert.cc:2947
#12 0x00007f3392cf1b50 in start_thread (arg=<optimized out>) at pthread_create.c:304
#13 0x00007f3390fa795d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:112

Trying to get some variables.
Some pointers may be invalid and cause the dump to abort.
Query (0x7f3377d96b20): 
Connection ID (thread ID): 1123
Status: KILL_CONNECTION

thread1:
	SELECT Id INTO @kill_id FROM INFORMATION_SCHEMA.PROCESSLIST WHERE Info LIKE 'REPLACE DELAYED%' LIMIT 1; KILL QUERY @kill_id ;

thread2:
	ALTER TABLE _table FORCE ;

query:
	REPLACE DELAYED INTO _table ( _field ) VALUES ( NULL ) ;

perl .runall-new.pl --threads=3 --duration=600 --queries=100M --grammar=test.yy --engine=MyISAM --basedir1=<your basedir> --vardir1=<your vardir>