crash_gen.py

#!/usr/bin/python3.7
###################################################################
#           Copyright (c) 2016 by TAOS Technologies, Inc.
#                     All rights reserved.
#
#  This file is proprietary and confidential to TAOS Technologies.
#  No part of this file may be reproduced, stored, transmitted,
#  disclosed or used in any form or by any means other than as
#  expressly provided by the written permission from Jianhui Tao
#
###################################################################

# -*- coding: utf-8 -*-
from __future__ import annotations  # For type hinting before definition, ref: https://stackoverflow.com/questions/33533148/how-do-i-specify-that-the-return-type-of-a-method-is-the-same-as-the-class-itsel    

import sys
import traceback
# Require Python 3
if sys.version_info[0] < 3:
    raise Exception("Must be using Python 3")

import getopt
import argparse
import copy

import threading
import random
import time
import logging
import datetime
import textwrap

from typing import List
from typing import Dict

from util.log import *
from util.dnodes import *
from util.cases import *
from util.sql import *

import crash_gen
import taos

# Global variables, tried to keep a small number. 
gConfig = None # Command-line/Environment Configurations, will set a bit later
logger = None

def runThread(wt: WorkerThread):    
    wt.run()

class CrashGenError(Exception):
    def __init__(self, msg=None, errno=None):
        self.msg = msg    
        self.errno = errno
    
    def __str__(self):
        return self.msg

class WorkerThread:
    def __init__(self, pool: ThreadPool, tid, 
            tc: ThreadCoordinator,
            # te: TaskExecutor,
            ): # note: main thread context!
        # self._curStep = -1 
        self._pool = pool
        self._tid = tid        
        self._tc = tc
        # self.threadIdent = threading.get_ident()
        self._thread = threading.Thread(target=runThread, args=(self,))
        self._stepGate = threading.Event()

        # Let us have a DB connection of our own
        if ( gConfig.per_thread_db_connection ): # type: ignore
            self._dbConn = DbConn()   

    def logDebug(self, msg):
        logger.info("    t[{}] {}".format(self._tid, msg))

    def logInfo(self, msg):
        logger.info("    t[{}] {}".format(self._tid, msg))

   
    def getTaskExecutor(self):
        return self._tc.getTaskExecutor()     

    def start(self):
        self._thread.start()  # AFTER the thread is recorded

    def run(self): 
        # initialization after thread starts, in the thread context
        # self.isSleeping = False
        logger.info("Starting to run thread: {}".format(self._tid))

        if ( gConfig.per_thread_db_connection ): # type: ignore
            self._dbConn.open()

        self._doTaskLoop()       
        
        # clean up
        if ( gConfig.per_thread_db_connection ): # type: ignore 
            self._dbConn.close()

    def _doTaskLoop(self) :
        # while self._curStep < self._pool.maxSteps:
        # tc = ThreadCoordinator(None)
        while True:  
            tc = self._tc # Thread Coordinator, the overall master            
            tc.crossStepBarrier()  # shared barrier first, INCLUDING the last one
            # logger.debug("Thread task loop exited barrier...")
            self.crossStepGate()   # then per-thread gate, after being tapped
            # logger.debug("Thread task loop exited step gate...")
            if not self._tc.isRunning():
                logger.debug("Thread Coordinator not running any more, worker thread now stopping...")
                break

            task = tc.fetchTask()
            task.execute(self)
            tc.saveExecutedTask(task)
  
    def verifyThreadSelf(self): # ensure we are called by this own thread
        if ( threading.get_ident() != self._thread.ident ): 
            raise RuntimeError("Unexpectly called from other threads")

    def verifyThreadMain(self): # ensure we are called by the main thread
        if ( threading.get_ident() != threading.main_thread().ident ): 
            raise RuntimeError("Unexpectly called from other threads")

    def verifyThreadAlive(self):
        if ( not self._thread.is_alive() ):
            raise RuntimeError("Unexpected dead thread")

    # A gate is different from a barrier in that a thread needs to be "tapped"
    def crossStepGate(self):
        self.verifyThreadAlive()
        self.verifyThreadSelf() # only allowed by ourselves
        
        # Wait again at the "gate", waiting to be "tapped"
        # logger.debug("Worker thread {} about to cross the step gate".format(self._tid))
        self._stepGate.wait() 
        self._stepGate.clear()
        
        # self._curStep += 1  # off to a new step...

    def tapStepGate(self): # give it a tap, release the thread waiting there
        self.verifyThreadAlive()
        self.verifyThreadMain() # only allowed for main thread
 
        # logger.debug("Tapping worker thread {}".format(self._tid))
        self._stepGate.set() # wake up!        
        time.sleep(0) # let the released thread run a bit

    def execSql(self, sql): # not "execute", since we are out side the DB context
        if ( gConfig.per_thread_db_connection ):
            return self._dbConn.execute(sql)            
        else:
            return self._tc.getDbState().getDbConn().execute(sql)

    # def querySql(self, sql): # not "execute", since we are out side the DB context
    #     if ( gConfig.per_thread_db_connection ):
    #         return self._dbConn.query(sql)            
    #     else:
    #         return self._tc.getDbState().getDbConn().query(sql)

class ThreadCoordinator:
    def __init__(self, pool, dbState):
        self._curStep = -1 # first step is 0
        self._pool = pool
        # self._wd = wd
        self._te = None # prepare for every new step
        self._dbState = dbState
        self._executedTasks: List[Task] = [] # in a given step
        self._lock = threading.RLock() # sync access for a few things

        self._stepBarrier = threading.Barrier(self._pool.numThreads + 1) # one barrier for all threads
        self._execStats = ExecutionStats()

    def getTaskExecutor(self):
        return self._te

    def getDbState(self) -> DbState :
        return self._dbState

    def crossStepBarrier(self):
        self._stepBarrier.wait()

    def run(self):              
        self._pool.createAndStartThreads(self)

        # Coordinate all threads step by step
        self._curStep = -1 # not started yet
        maxSteps = gConfig.max_steps # type: ignore
        self._execStats.startExec() # start the stop watch
        failed = False
        while(self._curStep < maxSteps-1 and not failed):  # maxStep==10, last curStep should be 9
            print(".", end="", flush=True)
            logger.debug("Main thread going to sleep")

            # Now ready to enter a step
            self.crossStepBarrier() # let other threads go past the pool barrier, but wait at the thread gate
            self._stepBarrier.reset() # Other worker threads should now be at the "gate"            

            # At this point, all threads should be pass the overall "barrier" and before the per-thread "gate"
            try:
                self._dbState.transition(self._executedTasks) # at end of step, transiton the DB state
            except taos.error.ProgrammingError as err:
                if ( err.msg == 'network unavailable' ): # broken DB connection
                    logger.info("DB connection broken, execution failed")
                    traceback.print_stack()
                    failed = True
                    self._te = None # Not running any more
                    self._execStats.registerFailure("Broken DB Connection")
                    # continue # don't do that, need to tap all threads at end, and maybe signal them to stop
                else:
                    raise 
            finally:
                pass
            
            self.resetExecutedTasks() # clear the tasks after we are done

            # Get ready for next step
            logger.info("<-- Step {} finished".format(self._curStep))
            self._curStep += 1 # we are about to get into next step. TODO: race condition here!                
            logger.debug("\r\n--> Step {} starts with main thread waking up".format(self._curStep)) # Now not all threads had time to go to sleep

            # A new TE for the new step
            if not failed: # only if not failed
                self._te = TaskExecutor(self._curStep)

            logger.debug("Main thread waking up at step {}, tapping worker threads".format(self._curStep)) # Now not all threads had time to go to sleep            
            self.tapAllThreads()

        logger.debug("Main thread ready to finish up...")
        if not failed: # only in regular situations
            self.crossStepBarrier() # Cross it one last time, after all threads finish
            self._stepBarrier.reset()
            logger.debug("Main thread in exclusive zone...")
            self._te = None # No more executor, time to end
            logger.debug("Main thread tapping all threads one last time...")
            self.tapAllThreads() # Let the threads run one last time

        logger.debug("Main thread joining all threads")
        self._pool.joinAll() # Get all threads to finish
        logger.info("All threads finished")
        self._execStats.endExec()

    def logStats(self):
        self._execStats.logStats()

    def tapAllThreads(self): # in a deterministic manner
        wakeSeq = []
        for i in range(self._pool.numThreads): # generate a random sequence
            if Dice.throw(2) == 1 :
                wakeSeq.append(i)
            else:
                wakeSeq.insert(0, i)
        logger.info("Waking up threads: {}".format(str(wakeSeq)))
        # TODO: set dice seed to a deterministic value
        for i in wakeSeq:
            self._pool.threadList[i].tapStepGate() # TODO: maybe a bit too deep?!
            time.sleep(0) # yield

    def isRunning(self):
        return self._te != None

    def fetchTask(self) -> Task :
        if ( not self.isRunning() ): # no task
            raise RuntimeError("Cannot fetch task when not running")
        # return self._wd.pickTask()
        # Alternatively, let's ask the DbState for the appropriate task
        # dbState = self.getDbState()
        # tasks = dbState.getTasksAtState() # TODO: create every time?
        # nTasks = len(tasks)
        # i = Dice.throw(nTasks)
        # logger.debug(" (dice:{}/{}) ".format(i, nTasks))
        # # return copy.copy(tasks[i]) # Needs a fresh copy, to save execution results, etc.
        # return tasks[i].clone() # TODO: still necessary?
        taskType = self.getDbState().pickTaskType() # pick a task type for current state
        return taskType(self.getDbState(), self._execStats) # create a task from it

    def resetExecutedTasks(self):
        self._executedTasks = [] # should be under single thread

    def saveExecutedTask(self, task):
        with self._lock:
            self._executedTasks.append(task)

# We define a class to run a number of threads in locking steps.
class ThreadPool:
    def __init__(self, dbState, numThreads, maxSteps, funcSequencer):
        self.numThreads = numThreads
        self.maxSteps = maxSteps
        self.funcSequencer = funcSequencer
        # Internal class variables
        # self.dispatcher = WorkDispatcher(dbState) # Obsolete?
        self.curStep = 0
        self.threadList = []
        # self.stepGate = threading.Condition() # Gate to hold/sync all threads
        # self.numWaitingThreads = 0    
        
    # starting to run all the threads, in locking steps
    def createAndStartThreads(self, tc: ThreadCoordinator):
        for tid in range(0, self.numThreads): # Create the threads
            workerThread = WorkerThread(self, tid, tc)            
            self.threadList.append(workerThread)
            workerThread.start() # start, but should block immediately before step 0

    def joinAll(self):
        for workerThread in self.threadList:
            logger.debug("Joining thread...")
            workerThread._thread.join()

# A queue of continguous POSITIVE integers
class LinearQueue():
    def __init__(self):
        self.firstIndex = 1  # 1st ever element
        self.lastIndex = 0
        self._lock = threading.RLock() # our functions may call each other
        self.inUse = set() # the indexes that are in use right now

    def toText(self):
        return "[{}..{}], in use: {}".format(self.firstIndex, self.lastIndex, self.inUse)

    # Push (add new element, largest) to the tail, and mark it in use
    def push(self): 
        with self._lock:
            # if ( self.isEmpty() ): 
            #     self.lastIndex = self.firstIndex 
            #     return self.firstIndex
            # Otherwise we have something
            self.lastIndex += 1
            self.allocate(self.lastIndex)
            # self.inUse.add(self.lastIndex) # mark it in use immediately
            return self.lastIndex

    def pop(self):
        with self._lock:
            if ( self.isEmpty() ): 
                # raise RuntimeError("Cannot pop an empty queue") 
                return False # TODO: None?
            
            index = self.firstIndex
            if ( index in self.inUse ):
                return False

            self.firstIndex += 1
            return index

    def isEmpty(self):
        return self.firstIndex > self.lastIndex

    def popIfNotEmpty(self):
        with self._lock:
            if (self.isEmpty()):
                return 0
            return self.pop()

    def allocate(self, i):
        with self._lock:
            # logger.debug("LQ allocating item {}".format(i))
            if ( i in self.inUse ):
                raise RuntimeError("Cannot re-use same index in queue: {}".format(i))
            self.inUse.add(i)

    def release(self, i):
        with self._lock:
            # logger.debug("LQ releasing item {}".format(i))
            self.inUse.remove(i) # KeyError possible, TODO: why?

    def size(self):
        return self.lastIndex + 1 - self.firstIndex

    def pickAndAllocate(self):
        if ( self.isEmpty() ):
            return None
        with self._lock:
            cnt = 0 # counting the interations
            while True:
                cnt += 1
                if ( cnt > self.size()*10 ): # 10x iteration already
                    # raise RuntimeError("Failed to allocate LinearQueue element")
                    return None
                ret = Dice.throwRange(self.firstIndex, self.lastIndex+1)
                if ( not ret in self.inUse ):
                    self.allocate(ret)
                    return ret

class DbConn:
    def __init__(self):
        self._conn = None 
        self._cursor = None
        self.isOpen = False
        
    def open(self): # Open connection
        if ( self.isOpen ):
            raise RuntimeError("Cannot re-open an existing DB connection")

        cfgPath = "../../build/test/cfg" 
        self._conn = taos.connect(host="127.0.0.1", config=cfgPath) # TODO: make configurable
        self._cursor = self._conn.cursor()

        # Get the connection/cursor ready
        self._cursor.execute('reset query cache')
        # self._cursor.execute('use db') # note we do this in _findCurrenState

        # Open connection
        self._tdSql = TDSql()
        self._tdSql.init(self._cursor)
        self.isOpen = True

    def resetDb(self): # reset the whole database, etc.
        if ( not self.isOpen ):
            raise RuntimeError("Cannot reset database until connection is open")
        # self._tdSql.prepare() # Recreate database, etc.

        self._cursor.execute('drop database if exists db')
        logger.debug("Resetting DB, dropped database")
        # self._cursor.execute('create database db')
        # self._cursor.execute('use db')

        # tdSql.execute('show databases')

    def close(self):
        if ( not self.isOpen ):
            raise RuntimeError("Cannot clean up database until connection is open")
        self._tdSql.close()
        self.isOpen = False

    def execute(self, sql): 
        if ( not self.isOpen ):
            raise RuntimeError("Cannot execute database commands until connection is open")
        return self._tdSql.execute(sql)

    def query(self, sql) :  # return rows affected
        if ( not self.isOpen ):
            raise RuntimeError("Cannot query database until connection is open")
        return self._tdSql.query(sql)
        # results are in: return self._tdSql.queryResult

    def _queryAny(self, sql) : # actual query result as an int
        if ( not self.isOpen ):
            raise RuntimeError("Cannot query database until connection is open")
        tSql = self._tdSql
        nRows = tSql.query(sql)
        if nRows != 1 :
            raise RuntimeError("Unexpected result for query: {}, rows = {}".format(sql, nRows))
        if tSql.queryRows != 1 or tSql.queryCols != 1:
            raise RuntimeError("Unexpected result set for query: {}".format(sql))
        return tSql.queryResult[0][0]

    def queryScalar(self, sql) -> int :
        return self._queryAny(sql)

    def queryString(self, sql) -> str :
        return self._queryAny(sql)
    
class AnyState:
    STATE_INVALID    = -1
    STATE_EMPTY      = 0  # nothing there, no even a DB
    STATE_DB_ONLY    = 1  # we have a DB, but nothing else
    STATE_TABLE_ONLY = 2  # we have a table, but totally empty
    STATE_HAS_DATA   = 3  # we have some data in the table
    _stateNames = ["Invalid", "Empty", "DB_Only", "Table_Only", "Has_Data"]

    STATE_VAL_IDX = 0
    CAN_CREATE_DB = 1
    CAN_DROP_DB = 2
    CAN_CREATE_FIXED_TABLE = 3
    CAN_DROP_FIXED_TABLE = 4
    CAN_ADD_DATA = 5
    CAN_READ_DATA = 6

    def __init__(self):
        self._info = self.getInfo()

    def __str__(self):
        return self._stateNames[self._info[self.STATE_VAL_IDX] - 1] # -1 hack to accomodate the STATE_INVALID case

    def getInfo(self):
        raise RuntimeError("Must be overriden by child classes")

    def verifyTasksToState(self, tasks, newState):
        raise RuntimeError("Must be overriden by child classes")

    def getValue(self):
        return self._info[self.STATE_VAL_IDX]
    def canCreateDb(self):
        return self._info[self.CAN_CREATE_DB]
    def canDropDb(self):
        return self._info[self.CAN_DROP_DB]
    def canCreateFixedTable(self):
        return self._info[self.CAN_CREATE_FIXED_TABLE]
    def canDropFixedTable(self):
        return self._info[self.CAN_DROP_FIXED_TABLE]
    def canAddData(self):
        return self._info[self.CAN_ADD_DATA]
    def canReadData(self):
        return self._info[self.CAN_READ_DATA]

    def assertAtMostOneSuccess(self, tasks, cls):
        sCnt = 0
        for task in tasks :
            if not isinstance(task, cls):
                continue
            if task.isSuccess():
                task.logDebug("Task success found")
                sCnt += 1
                if ( sCnt >= 2 ):
                    raise RuntimeError("Unexpected more than 1 success with task: {}".format(cls))

    def assertIfExistThenSuccess(self, tasks, cls):
        sCnt = 0
        exists = False
        for task in tasks :
            if not isinstance(task, cls):
                continue
            exists = True # we have a valid instance
            if task.isSuccess():
                sCnt += 1
        if ( exists and sCnt <= 0 ):
            raise RuntimeError("Unexpected zero success for task: {}".format(cls))

    def assertNoTask(self, tasks, cls):
        for task in tasks :
            if isinstance(task, cls):
                raise CrashGenError("This task: {}, is not expected to be present, given the success/failure of others".format(cls.__name__))

    def assertNoSuccess(self, tasks, cls):
        for task in tasks :
            if isinstance(task, cls):
                if task.isSuccess():
                    raise RuntimeError("Unexpected successful task: {}".format(cls))

    def hasSuccess(self, tasks, cls):
        for task in tasks :
            if not isinstance(task, cls):
                continue
            if task.isSuccess():
                return True
        return False

class StateInvalid(AnyState):
    def getInfo(self):
        return [
            self.STATE_INVALID,
            False, False, # can create/drop Db
            False, False, # can create/drop fixed table
            False, False, # can insert/read data with fixed table
        ]

    # def verifyTasksToState(self, tasks, newState):

class StateEmpty(AnyState):
    def getInfo(self):
        return [
            self.STATE_EMPTY,
            True, False, # can create/drop Db
            False, False, # can create/drop fixed table
            False, False, # can insert/read data with fixed table
        ]

    def verifyTasksToState(self, tasks, newState):
        if ( self.hasSuccess(tasks, CreateDbTask) ):
            self.assertAtMostOneSuccess(tasks, CreateDbTask) # not really valid for massively parrallel tasks

class StateDbOnly(AnyState):
    def getInfo(self):
        return [
            self.STATE_DB_ONLY,
            False, True,
            True, False,
            False, False,
        ]

    def verifyTasksToState(self, tasks, newState):
        self.assertAtMostOneSuccess(tasks, DropDbTask) # not true in massively parralel cases
        self.assertIfExistThenSuccess(tasks, DropDbTask)
        self.assertAtMostOneSuccess(tasks, CreateFixedTableTask) 
        # Nothing to be said about adding data task
        if ( self.hasSuccess(tasks, DropDbTask) ): # dropped the DB
            # self.assertHasTask(tasks, DropDbTask) # implied by hasSuccess
            self.assertAtMostOneSuccess(tasks, DropDbTask)
            # self._state = self.STATE_EMPTY
        elif ( self.hasSuccess(tasks, CreateFixedTableTask) ): # did not drop db, create table success
            # self.assertHasTask(tasks, CreateFixedTableTask) # tried to create table
            self.assertAtMostOneSuccess(tasks, CreateFixedTableTask) # at most 1 attempt is successful
            self.assertNoTask(tasks, DropDbTask) # should have have tried
            # if ( not self.hasSuccess(tasks, AddFixedDataTask) ): # just created table, no data yet
            #     # can't say there's add-data attempts, since they may all fail
            #     self._state = self.STATE_TABLE_ONLY
            # else:                    
            #     self._state = self.STATE_HAS_DATA
        # What about AddFixedData?
        # elif ( self.hasSuccess(tasks, AddFixedDataTask) ):
        #     self._state = self.STATE_HAS_DATA
        # else: # no success in dropping db tasks, no success in create fixed table? read data should also fail
        #     # raise RuntimeError("Unexpected no-success scenario")   # We might just landed all failure tasks, 
        #     self._state = self.STATE_DB_ONLY  # no change

class StateTableOnly(AnyState):
    def getInfo(self):
        return [
            self.STATE_TABLE_ONLY,
            False, True,
            False, True,
            True, True,
        ]

    def verifyTasksToState(self, tasks, newState):
        if ( self.hasSuccess(tasks, DropFixedTableTask) ): # we are able to drop the table
            self.assertAtMostOneSuccess(tasks, DropFixedTableTask)
            # self._state = self.STATE_DB_ONLY
        elif ( self.hasSuccess(tasks, AddFixedDataTask) ): # no success dropping the table, but added data
            self.assertNoTask(tasks, DropFixedTableTask)
            # self._state = self.STATE_HAS_DATA
        elif ( self.hasSuccess(tasks, ReadFixedDataTask) ): # no success in prev cases, but was able to read data
            self.assertNoTask(tasks, DropFixedTableTask)
            self.assertNoTask(tasks, AddFixedDataTask)
            # self._state = self.STATE_TABLE_ONLY # no change
        else: # did not drop table, did not insert data, did not read successfully, that is impossible
            raise RuntimeError("Unexpected no-success scenarios")

class StateHasData(AnyState):
    def getInfo(self):
        return [
            self.STATE_HAS_DATA,
            False, True,
            False, True,
            True, True,
        ]

    def verifyTasksToState(self, tasks, newState):
        if ( self.hasSuccess(tasks, DropFixedTableTask) ):
                self.assertAtMostOneSuccess(tasks, DropFixedTableTask)
                # self._state = self.STATE_DB_ONLY
        else: # no success dropping the table, table remains intact in this step
            self.assertNoTask(tasks, DropFixedTableTask) # we should not have had such a task

            if ( not self.hasSuccess(tasks, AddFixedDataTask) ): # added data
                # self._state = self.STATE_HAS_DATA
            # else:
                self.assertNoTask(tasks, AddFixedDataTask)
                if ( not self.hasSuccess(tasks, ReadFixedDataTask) ): # simple able to read some data
                    # which is ok, then no state change
                #     self._state = self.STATE_HAS_DATA # no change
                # else: # did not drop table, did not insert data, that is impossible? yeah, we might only had ReadData task
                    raise RuntimeError("Unexpected no-success scenarios")

# State of the database as we believe it to be
class DbState():
    
    def __init__(self):
        self.tableNumQueue = LinearQueue()
        self._lastTick = datetime.datetime(2019, 1, 1) # initial date time tick
        self._lastInt  = 0 # next one is initial integer 
        self._lock = threading.RLock()

        self._state = StateInvalid() # starting state
        self._stateWeights = [1,3,5,10]
        
        # self.openDbServerConnection()
        self._dbConn = DbConn()
        try:
            self._dbConn.open() # may throw taos.error.ProgrammingError: disconnected
        except taos.error.ProgrammingError as err:
            # print("Error type: {}, msg: {}, value: {}".format(type(err), err.msg, err))
            if ( err.msg == 'disconnected' ): # cannot open DB connection
                print("Cannot establish DB connection, please re-run script without parameter, and follow the instructions.")
                sys.exit()
            else:
                raise            
        except:
            print("[=]Unexpected exception")
            raise        
        self._dbConn.resetDb() # drop and recreate DB
        self._state = StateEmpty() # initial state, the result of above

    def getDbConn(self):
        return self._dbConn

    def pickAndAllocateTable(self): # pick any table, and "use" it
        return self.tableNumQueue.pickAndAllocate()

    def addTable(self):
        with self._lock:
            tIndex = self.tableNumQueue.push()
        return tIndex

    def getFixedTableName(self):
        return "fixed_table"

    def releaseTable(self, i): # return the table back, so others can use it
        self.tableNumQueue.release(i)

    def getNextTick(self):
        with self._lock: # prevent duplicate tick
            self._lastTick += datetime.timedelta(0, 1) # add one second to it
            return self._lastTick

    def getNextInt(self):
        with self._lock:
            self._lastInt += 1
            return self._lastInt
    
    def getTableNameToDelete(self):
        tblNum = self.tableNumQueue.pop() # TODO: race condition!
        if ( not tblNum ): # maybe false
            return False
        
        return "table_{}".format(tblNum)

    def cleanUp(self):
        self._dbConn.close()      

    def getTaskTypesAtState(self):
        allTaskClasses = StateTransitionTask.__subclasses__() # all state transition tasks
        taskTypes = []
        for tc in allTaskClasses:
            # t = tc(self) # create task object
            if tc.canBeginFrom(self._state):
                taskTypes.append(tc)
        if len(taskTypes) <= 0:
            raise RuntimeError("No suitable task types found for state: {}".format(self._state))
        return taskTypes

        # tasks.append(ReadFixedDataTask(self)) # always for everybody
        # if ( self._state == self.STATE_EMPTY ):
        #     tasks.append(CreateDbTask(self))
        #     tasks.append(CreateFixedTableTask(self))
        # elif ( self._state == self.STATE_DB_ONLY ):
        #     tasks.append(DropDbTask(self))
        #     tasks.append(CreateFixedTableTask(self))
        #     tasks.append(AddFixedDataTask(self))
        # elif ( self._state == self.STATE_TABLE_ONLY ):
        #     tasks.append(DropFixedTableTask(self))
        #     tasks.append(AddFixedDataTask(self))
        # elif ( self._state == self.STATE_HAS_DATA ) : # same as above. TODO: adjust
        #     tasks.append(DropFixedTableTask(self))
        #     tasks.append(AddFixedDataTask(self))
        # else:
        #     raise RuntimeError("Unexpected DbState state: {}".format(self._state))
        # return tasks

    def pickTaskType(self):
        taskTypes = self.getTaskTypesAtState() # all the task types we can choose from at curent state
        weights = []
        for tt in taskTypes:
            endState = tt.getEndState()
            if endState != None :
                weights.append(self._stateWeights[endState]) # TODO: change to a method
            else:
                weights.append(10) # read data task, default to 10: TODO: change to a constant
        i = self._weighted_choice_sub(weights)
        # logger.debug(" (weighted random:{}/{}) ".format(i, len(taskTypes)))        
        return taskTypes[i]

    def _weighted_choice_sub(self, weights): # ref: https://eli.thegreenplace.net/2010/01/22/weighted-random-generation-in-python/
        rnd = random.random() * sum(weights) # TODO: use our dice to ensure it being determinstic?
        for i, w in enumerate(weights):
            rnd -= w
            if rnd < 0:
                return i

    def _findCurrentState(self):
        dbc = self._dbConn
        if dbc.query("show databases") == 0 : # no database?!
            return StateEmpty()
        dbc.execute("use db") # did not do this when openning connection
        if dbc.query("show tables") == 0 : # no tables
            return StateDbOnly()
        if dbc.query("SELECT * FROM {}".format(self.getFixedTableName()) ) == 0 : # no data
            return StateTableOnly()
        else:
            return StateHasData()
    
    def transition(self, tasks):
        if ( len(tasks) == 0 ): # before 1st step, or otherwise empty
            return # do nothing

        self._dbConn.execute("show dnodes") # this should show up in the server log, separating steps

        # Generic Checks, first based on the start state
        if self._state.canCreateDb():
            self._state.assertIfExistThenSuccess(tasks, CreateDbTask)
            # self.assertAtMostOneSuccess(tasks, CreateDbTask) # not really, in case of multiple creation and drops

        if self._state.canDropDb():
            self._state.assertIfExistThenSuccess(tasks, DropDbTask)
            # self.assertAtMostOneSuccess(tasks, DropDbTask) # not really in case of drop-create-drop

        # if self._state.canCreateFixedTable():
            # self.assertIfExistThenSuccess(tasks, CreateFixedTableTask) # Not true, DB may be dropped
            # self.assertAtMostOneSuccess(tasks, CreateFixedTableTask) # not really, in case of create-drop-create

        # if self._state.canDropFixedTable():
            # self.assertIfExistThenSuccess(tasks, DropFixedTableTask) # Not True, the whole DB may be dropped
            # self.assertAtMostOneSuccess(tasks, DropFixedTableTask) # not really in case of drop-create-drop

        # if self._state.canAddData():
        #     self.assertIfExistThenSuccess(tasks, AddFixedDataTask)  # not true actually

        # if self._state.canReadData():
            # Nothing for sure

        newState = self._findCurrentState()
        self._state.verifyTasksToState(tasks, newState) # can old state move to new state through the tasks?

        self._state = newState
        logger.debug("New DB state is: {}".format(self._state))

class TaskExecutor():
    def __init__(self, curStep):
        self._curStep = curStep

    def getCurStep(self):
        return self._curStep

    def execute(self, task: Task, wt: WorkerThread): # execute a task on a thread
        task.execute(wt)

    # def logInfo(self, msg):
    #     logger.info("    T[{}.x]: ".format(self._curStep) + msg)

    # def logDebug(self, msg):
    #     logger.debug("    T[{}.x]: ".format(self._curStep) + msg)

class Task():
    taskSn = 100

    @classmethod
    def allocTaskNum(cls):
        cls.taskSn += 1
        return cls.taskSn

    def __init__(self, dbState: DbState, execStats: ExecutionStats):
        self._dbState = dbState
        self._workerThread = None 
        self._err = None
        self._curStep = None
        self._numRows = None # Number of rows affected

        # Assign an incremental task serial number        
        self._taskNum = self.allocTaskNum()

        self._execStats = execStats

    def isSuccess(self):
        return self._err == None

    def clone(self): # TODO: why do we need this again?
        newTask = self.__class__(self._dbState, self._execStats)
        return newTask

    def logDebug(self, msg):
        self._workerThread.logDebug("s[{}.{}] {}".format(self._curStep, self._taskNum, msg))

    def logInfo(self, msg):
        self._workerThread.logInfo("s[{}.{}] {}".format(self._curStep, self._taskNum, msg))

    def _executeInternal(self, te: TaskExecutor, wt: WorkerThread):
        raise RuntimeError("To be implemeted by child classes, class name: {}".format(self.__class__.__name__))

    def execute(self, wt: WorkerThread):
        wt.verifyThreadSelf()
        self._workerThread = wt # type: ignore

        te = wt.getTaskExecutor()
        self._curStep = te.getCurStep()
        self.logDebug("[-] executing task {}...".format(self.__class__.__name__))

        self._err = None
        self._execStats.beginTaskType(self.__class__.__name__) # mark beginning
        try:
            self._executeInternal(te, wt) # TODO: no return value?
        except taos.error.ProgrammingError as err:
            self.logDebug("[=]Taos Execution exception: {0}".format(err))
            self._err = err
        except:
            self.logDebug("[=]Unexpected exception")
            raise
        self._execStats.endTaskType(self.__class__.__name__, self.isSuccess())
        
        self.logDebug("[X] task execution completed, {}, status: {}".format(self.__class__.__name__, "Success" if self.isSuccess() else "Failure"))        
        self._execStats.incExecCount(self.__class__.__name__, self.isSuccess()) # TODO: merge with above.

    def execSql(self, sql):
        return self._dbState.execute(sql)

                  
class ExecutionStats:    
    def __init__(self):
        self._execTimes: Dict[str, [int, int]] = {} # total/success times for a task
        self._tasksInProgress = 0
        self._lock = threading.Lock()
        self._firstTaskStartTime = None
        self._execStartTime = None
        self._elapsedTime = 0.0 # total elapsed time
        self._accRunTime = 0.0 # accumulated run time

        self._failed = False
        self._failureReason = None

    def startExec(self):
        self._execStartTime = time.time()

    def endExec(self):
        self._elapsedTime = time.time() - self._execStartTime

    def incExecCount(self, klassName, isSuccess): # TODO: add a lock here
        if klassName not in self._execTimes:
            self._execTimes[klassName] = [0, 0]
        t = self._execTimes[klassName] # tuple for the data
        t[0] += 1 # index 0 has the "total" execution times
        if isSuccess:
            t[1] += 1 # index 1 has the "success" execution times

    def beginTaskType(self, klassName):
        with self._lock:
            if self._tasksInProgress == 0 : # starting a new round
                self._firstTaskStartTime = time.time() # I am now the first task
            self._tasksInProgress += 1

    def endTaskType(self, klassName, isSuccess):
        with self._lock:
            self._tasksInProgress -= 1
            if self._tasksInProgress == 0 : # all tasks have stopped
                self._accRunTime += (time.time() - self._firstTaskStartTime)
                self._firstTaskStartTime = None

    def registerFailure(self, reason):
        self._failed = True
        self._failureReason = reason

    def logStats(self):
        logger.info("----------------------------------------------------------------------")
        logger.info("| Crash_Gen test {}, with the following stats:".
            format("FAILED (reason: {})".format(self._failureReason) if self._failed else "SUCCEEDED"))
        logger.info("| Task Execution Times (success/total):")
        execTimesAny = 0
        for k, n in self._execTimes.items():            
            execTimesAny += n[1]
            logger.info("|    {0:<24}: {1}/{2}".format(k,n[1],n[0]))
                
        logger.info("| Total Tasks Executed (success or not): {} ".format(execTimesAny))
        logger.info("| Total Tasks In Progress at End: {}".format(self._tasksInProgress))
        logger.info("| Total Task Busy Time (elapsed time when any task is in progress): {:.3f} seconds".format(self._accRunTime))
        logger.info("| Average Per-Task Execution Time: {:.3f} seconds".format(self._accRunTime/execTimesAny))
        logger.info("| Total Elapsed Time (from wall clock): {:.3f} seconds".format(self._elapsedTime))
        logger.info("----------------------------------------------------------------------")
        


class StateTransitionTask(Task):
    # @classmethod
    # def getAllTaskClasses(cls): # static
    #     return cls.__subclasses__()
    @classmethod
    def getInfo(cls): # each sub class should supply their own information
        raise RuntimeError("Overriding method expected")

    # @classmethod
    # def getBeginStates(cls):
    #     return cls.getInfo()[0]

    @classmethod
    def getEndState(cls):
        return cls.getInfo()[0]

    @classmethod
    def canBeginFrom(cls, state: AnyState):
        # return state.getValue() in cls.getBeginStates()
        raise RuntimeError("must be overriden")

    def execute(self, wt: WorkerThread):
        super().execute(wt)
        


class CreateDbTask(StateTransitionTask):
    @classmethod
    def getInfo(cls):
        return [
            # [AnyState.STATE_EMPTY], # can begin from
            AnyState.STATE_DB_ONLY # end state
        ]

    @classmethod
    def canBeginFrom(cls, state: AnyState):
        return state.canCreateDb()

    def _executeInternal(self, te: TaskExecutor, wt: WorkerThread):
        wt.execSql("create database db")

class DropDbTask(StateTransitionTask):
    @classmethod
    def getInfo(cls):
        return [
            # [AnyState.STATE_DB_ONLY, AnyState.STATE_TABLE_ONLY, AnyState.STATE_HAS_DATA],
            AnyState.STATE_EMPTY
        ]

    @classmethod
    def canBeginFrom(cls, state: AnyState):
        return state.canDropDb()

    def _executeInternal(self, te: TaskExecutor, wt: WorkerThread):
        wt.execSql("drop database db")

class CreateFixedTableTask(StateTransitionTask):
    @classmethod
    def getInfo(cls):
        return [
            # [AnyState.STATE_DB_ONLY],
            AnyState.STATE_TABLE_ONLY
        ]

    @classmethod
    def canBeginFrom(cls, state: AnyState):
        return state.canCreateFixedTable()

    def _executeInternal(self, te: TaskExecutor, wt: WorkerThread):
        tblName = self._dbState.getFixedTableName()        
        wt.execSql("create table db.{} (ts timestamp, speed int)".format(tblName))

class ReadFixedDataTask(StateTransitionTask):
    @classmethod
    def getInfo(cls):
        return [
            # [AnyState.STATE_TABLE_ONLY, AnyState.STATE_HAS_DATA],
            None # meaning doesn't affect state
        ]

    @classmethod
    def canBeginFrom(cls, state: AnyState):
        return state.canReadData()

    def _executeInternal(self, te: TaskExecutor, wt: WorkerThread):
        tblName = self._dbState.getFixedTableName()        
        wt.execSql("select * from db.{}".format(tblName)) # TODO: analyze result set later
        # tdSql.query(" cars where tbname in ('carzero', 'carone')")

class DropFixedTableTask(StateTransitionTask):
    @classmethod
    def getInfo(cls):
        return [
            # [AnyState.STATE_TABLE_ONLY, AnyState.STATE_HAS_DATA],
            AnyState.STATE_DB_ONLY # meaning doesn't affect state
        ]

    @classmethod
    def canBeginFrom(cls, state: AnyState):
        return state.canDropFixedTable()

    def _executeInternal(self, te: TaskExecutor, wt: WorkerThread):
        tblName = self._dbState.getFixedTableName()        
        wt.execSql("drop table db.{}".format(tblName))

class AddFixedDataTask(StateTransitionTask):
    @classmethod
    def getInfo(cls):
        return [
            # [AnyState.STATE_TABLE_ONLY, AnyState.STATE_HAS_DATA],
            AnyState.STATE_HAS_DATA
        ]

    @classmethod
    def canBeginFrom(cls, state: AnyState):
        return state.canAddData()
        
    def _executeInternal(self, te: TaskExecutor, wt: WorkerThread):
        ds = self._dbState
        sql = "insert into db.{} values ('{}', {});".format(ds.getFixedTableName(), ds.getNextTick(), ds.getNextInt())
        wt.execSql(sql) 


#---------- Non State-Transition Related Tasks ----------#

class CreateTableTask(Task):    
    def _executeInternal(self, te: TaskExecutor, wt: WorkerThread):
        tIndex = self._dbState.addTable()
        self.logDebug("Creating a table {} ...".format(tIndex))
        wt.execSql("create table db.table_{} (ts timestamp, speed int)".format(tIndex))
        self.logDebug("Table {} created.".format(tIndex))
        self._dbState.releaseTable(tIndex)

class DropTableTask(Task):
    def _executeInternal(self, te: TaskExecutor, wt: WorkerThread):
        tableName = self._dbState.getTableNameToDelete()
        if ( not tableName ): # May be "False"
            self.logInfo("Cannot generate a table to delete, skipping...")
            return
        self.logInfo("Dropping a table db.{} ...".format(tableName))
        wt.execSql("drop table db.{}".format(tableName))
        


class AddDataTask(Task):
    def _executeInternal(self, te: TaskExecutor, wt: WorkerThread):
        ds = self._dbState
        self.logInfo("Adding some data... numQueue={}".format(ds.tableNumQueue.toText()))
        tIndex = ds.pickAndAllocateTable()
        if ( tIndex == None ):
            self.logInfo("No table found to add data, skipping...")
            return
        sql = "insert into db.table_{} values ('{}', {});".format(tIndex, ds.getNextTick(), ds.getNextInt())
        self.logDebug("Executing SQL: {}".format(sql))
        wt.execSql(sql) 
        ds.releaseTable(tIndex)
        self.logDebug("Finished adding data")


# Deterministic random number generator
class Dice():
    seeded = False # static, uninitialized

    @classmethod
    def seed(cls, s): # static
        if (cls.seeded):
            raise RuntimeError("Cannot seed the random generator more than once")
        cls.verifyRNG()
        random.seed(s)
        cls.seeded = True  # TODO: protect against multi-threading

    @classmethod
    def verifyRNG(cls): # Verify that the RNG is determinstic
        random.seed(0)
        x1 = random.randrange(0, 1000)
        x2 = random.randrange(0, 1000)
        x3 = random.randrange(0, 1000)
        if ( x1 != 864 or x2!=394 or x3!=776 ):
            raise RuntimeError("System RNG is not deterministic")

    @classmethod
    def throw(cls, stop): # get 0 to stop-1
        return cls.throwRange(0, stop)

    @classmethod
    def throwRange(cls, start, stop): # up to stop-1
        if ( not cls.seeded ):
            raise RuntimeError("Cannot throw dice before seeding it")
        return random.randrange(start, stop)


# Anyone needing to carry out work should simply come here
# class WorkDispatcher():
#     def __init__(self, dbState):
#         # self.totalNumMethods = 2
#         self.tasks = [
#             # CreateTableTask(dbState), # Obsolete
#             # DropTableTask(dbState),
#             # AddDataTask(dbState),
#         ]

#     def throwDice(self):
#         max = len(self.tasks) - 1 
#         dRes = random.randint(0, max)
#         # logger.debug("Threw the dice in range [{},{}], and got: {}".format(0,max,dRes))
#         return dRes

#     def pickTask(self):
#         dice = self.throwDice()
#         return self.tasks[dice]

#     def doWork(self, workerThread):
#         task = self.pickTask()
#         task.execute(workerThread)

def main():
    # Super cool Python argument library: https://docs.python.org/3/library/argparse.html
    parser = argparse.ArgumentParser(
        formatter_class=argparse.RawDescriptionHelpFormatter,
        description=textwrap.dedent('''\
            TDengine Auto Crash Generator (PLEASE NOTICE the Prerequisites Below)
            ---------------------------------------------------------------------
            1. You build TDengine in the top level ./build directory, as described in offical docs
            2. You run the server there before this script: ./build/bin/taosd -c test/cfg

            '''))
    parser.add_argument('-p', '--per-thread-db-connection', action='store_true',                        
                        help='Use a single shared db connection (default: false)')
    parser.add_argument('-d', '--debug', action='store_true',                        
                        help='Turn on DEBUG mode for more logging (default: false)')
    parser.add_argument('-s', '--max-steps', action='store', default=100, type=int,
                        help='Maximum number of steps to run (default: 100)')
    parser.add_argument('-t', '--num-threads', action='store', default=10, type=int,
                        help='Number of threads to run (default: 10)')

    global gConfig
    gConfig = parser.parse_args()
    if len(sys.argv) == 1:
        parser.print_help()
        sys.exit()

    global logger
    logger = logging.getLogger('CrashGen')
    if ( gConfig.debug ):
        logger.setLevel(logging.DEBUG) # default seems to be INFO        
    ch = logging.StreamHandler()
    logger.addHandler(ch)

    dbState = DbState()
    Dice.seed(0) # initial seeding of dice
    tc = ThreadCoordinator(
        ThreadPool(dbState, gConfig.num_threads, gConfig.max_steps, 0), 
        # WorkDispatcher(dbState), # Obsolete?
        dbState
        )
    
    tc.run()
    tc.logStats()
    dbState.cleanUp()    
    
    logger.info("Finished running thread pool")

if __name__ == "__main__":
    main()