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Thread.c
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2009-03-26
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code Thread
-- Harry Porter -- January 10, 2005
----------------------------- InitializeScheduler ---------------------------------
function InitializeScheduler ()
--
-- This routine assumes that we are in System mode. It sets up the
-- thread scheduler and turns the executing program into "main-thread".
-- After exit, we can execute "Yield", "Fork", etc. Upon return, the
-- main-thread will be executing with interrupts enabled.
--
Cleari ()
print ("Initializing Thread Scheduler...\n")
readyList = new List [Thread]
threadsToBeDestroyed = new List [Thread]
mainThread = new Thread
mainThread.Init ("main-thread")
mainThread.status = RUNNING
idleThread = new Thread
idleThread.Init ("idle-thread")
idleThread.Fork (IdleFunction, 0)
currentThread = & mainThread
currentInterruptStatus = ENABLED
Seti ()
endFunction
----------------------------- IdleFunction ---------------------------------
function IdleFunction (arg: int)
--
-- This is the "idle thread", a kernel thread which ensures that the ready
-- list is never empty. The idle thread constantly yields to other threads
-- in an infinite loop. However, before yielding, it first checks to see if
-- there are other threads. If there are no other threads, the idle thread
-- will execute the "wait" instruction. The "wait" instruction will enable
-- interrupts and halt CPU execution until the next interrupt arrives.
--
var junk: int
while true
junk = SetInterruptsTo (DISABLED)
if readyList.IsEmpty ()
Wait ()
else
currentThread.Yield ()
endIf
endWhile
endFunction
----------------------------- Run ---------------------------------
function Run (nextThread: ptr to Thread)
--
-- Begin executing the thread "nextThread", which has already
-- been removed from the readyList. The current thread will
-- be suspended; we assume that its status has already been
-- changed to READY or BLOCKED. We assume that interrupts are
-- DISABLED when called.
--
-- This routine is called only from "Thread.Yield" and "Thread.Sleep".
--
var prevThread, th: ptr to Thread
prevThread = currentThread
prevThread.CheckOverflow ()
currentThread = nextThread
nextThread.status = RUNNING
--print ("SWITCHING from ")
--print (prevThread.name)
--print (" to ")
--print (nextThread.name)
--print ("\n")
Switch (prevThread, nextThread)
--print ("After SWITCH, back in thread ")
--print (currentThread.name)
--print ("\n")
while ! threadsToBeDestroyed.IsEmpty ()
th = threadsToBeDestroyed.Remove()
th.status = UNUSED
endWhile
endFunction
----------------------------- PrintReadyList ---------------------------------
function PrintReadyList ()
--
-- This routine prints the readyList. It disables interrupts during the
-- printing to guarantee that the readyList won't change while it is
-- being printed, which could cause disaster in this routine!
--
var oldStatus: int
oldStatus = SetInterruptsTo (DISABLED)
print ("Here is the ready list:\n")
readyList.ApplyToEach (ThreadPrint)
oldStatus = SetInterruptsTo (oldStatus)
endFunction
----------------------------- ThreadStartMain ---------------------------------
function ThreadStartMain ()
--
-- This function is called from the assembly language routine "ThreadStart".
-- It is the first KPL code each thread will execute, and it will
-- invoke the thread's "main" function, with interrupts enabled. If the "main"
-- function ever returns, this function will terminate this thread. This
-- function will never return.
--
var
junk: int
mainFun: ptr to function (int)
-- print ("ThreadStartMain...\n")
junk = SetInterruptsTo (ENABLED)
mainFun = currentThread.initialFunction
mainFun (currentThread.initialArgument)
ThreadFinish ()
FatalError ("ThreadFinish should never return")
endFunction
----------------------------- ThreadFinish ---------------------------------
function ThreadFinish ()
--
-- As the last thing to do in this thread, we want to clean up
-- and reclaim the Thread object. This method is called as the
-- last thing the thread does; this is the normal way for a thread
-- to die. However, since the thread is still running in this,
-- we can't actually do the clean up. So we just make a note
-- that it is pending. After the next thread starts (in method "Run")
-- we'll finish the job.
--
var junk: int
junk = SetInterruptsTo (DISABLED)
-- print ("Finishing ")
-- print (currentThread.name)
-- print ("\n")
threadsToBeDestroyed.AddToEnd (currentThread)
currentThread.Sleep ()
-- Execution will never reach the next instruction
debug
endFunction
----------------------------- FatalError ---------------------------------
function FatalError (errorMessage: ptr to array of char)
--
-- Print out the name of the current thread and the given error message.
-- Then abort execution.
--
var
junk: int
junk = SetInterruptsTo (DISABLED)
print ("\nFATAL ERROR")
if currentThread -- If case errors occur before thread initialization
print (" in ")
print (currentThread.name)
endIf
print (": \"")
print (errorMessage)
print ("\" -- TERMINATING!\n")
RuntimeExit ()
endFunction
----------------------------- SetInterruptsTo ---------------------------------
function SetInterruptsTo (newStatus: int) returns int
--
-- This routine is passed a status (DISABLED or ENABLED). It
-- returns the previous interrupt status and sets the interrupt
-- status to "newStatus".
--
-- Since this routine reads and modifies a shared variable
-- (currentInterruptStatus), there is a danger of this routine
-- being re-entered. Therefore, it momentarily will disable
-- interrupts, to ensure a valid update to this variable.
--
var
oldStat: int
Cleari ()
oldStat = currentInterruptStatus
if newStatus == ENABLED
currentInterruptStatus = ENABLED
Seti ()
else
currentInterruptStatus = DISABLED
Cleari ()
endIf
return oldStat
endFunction
----------------------------- TimerInterruptHandler ---------------------------------
function TimerInterruptHandler ()
--
-- This routine is called when a timer interrupt occurs. Upon entry,
-- interrupts are DISABLED. Upon return, execution will return to
-- the interrupted process, which necessarily had interrupts ENABLED.
--
-- (If you wish to turn time-slicing off, simply disable the call
-- to "Yield" in the code below. Threads will then execute until they
-- call "Yield" explicitly, or until they call "Sleep".)
--
currentInterruptStatus = DISABLED
-- printChar ('_')
currentThread.Yield ()
currentInterruptStatus = ENABLED
endFunction
----------------------------- ThreadPrint ---------------------------------
function ThreadPrint (t: ptr to Thread)
--
-- This function prints a single line giving the name of thread "t",
-- its status, and the address of the Thread object itself (which may be
-- helpful in disnguishing Threads when the name is not helpful).
--
var
oldStatus: int = SetInterruptsTo (DISABLED)
print (" Thread \"")
print (t.name)
print ("\" status=")
switch t.status
case JUST_CREATED:
print ("JUST_CREATED")
break
case READY:
print ("READY")
break
case RUNNING:
print ("RUNNING")
break
case BLOCKED:
print ("BLOCKED")
break
case UNUSED:
print ("UNUSED")
break
default:
FatalError ("Bad status in Thread")
endSwitch
print (" (addr of Thread object: ")
printHex (t asInteger)
print (")")
nl ()
-- t.Print ()
oldStatus = SetInterruptsTo (oldStatus)
endFunction
----------------------------- Thread ---------------------------------
behavior Thread
---------- Thread . Init ----------
method Init (n: String)
--
-- Initialize this Thread object, but do not schedule it for
-- execution yet.
--
name = n
status = JUST_CREATED
-- The next line initializes the systemStack array, without filling it in.
*((& systemStack) asPtrTo int) = SYSTEM_STACK_SIZE
systemStack [0] = STACK_SENTINEL
systemStack [SYSTEM_STACK_SIZE-1] = STACK_SENTINEL
stackTop = & (systemStack[SYSTEM_STACK_SIZE-1])
regs = new array of int { 13 of 0 }
endMethod
---------- Thread . Fork ----------
method Fork (fun: ptr to function (int), arg: int)
--
-- This method will schedule this thread for execution; in other words
-- it will make it ready to run by adding it to the "ready queue." This
-- method is passed a function and a single integer argument. When the
-- thread runs, the thread will execute this function on that argument
-- and then termiante. This method will return after scheduling this
-- thread.
--
var
oldIntStat, junk: int
oldIntStat = SetInterruptsTo (DISABLED)
-- print ("Forking thread...\n")
initialFunction = fun
initialArgument = arg
stackTop = stackTop - 4
*(stackTop asPtrTo int) = ThreadStartUp asInteger
status = READY
readyList.AddToEnd (self)
junk = SetInterruptsTo (oldIntStat)
endMethod
---------- Thread . Yield ----------
method Yield ()
--
-- This method should only be invoked on the current thread. The
-- current thread may yield the processor to other threads by
-- executing:
-- currentThread.Yield ()
-- This method may be invoked with or without interrupts enabled.
-- Upon return, the interrupts will be in the same state; however
-- since other threads are given a chance to run and they may allow
-- interrupts, interrupts handlers may have been invoked before
-- this method returns.
--
var
nextTh: ptr to Thread
oldIntStat, junk: int
-- ASSERT:
if self != currentThread
FatalError ("In Yield, self != currentThread")
endIf
oldIntStat = SetInterruptsTo (DISABLED)
-- print ("Yielding ")
-- print (name)
-- print ("\n")
nextTh = readyList.Remove ()
if nextTh
-- print ("About to run ")
-- print (nextTh.name)
-- print ("\n")
if status == BLOCKED
FatalError ("Status of current thread should be READY or RUNNING")
endIf
status = READY
readyList.AddToEnd (self)
Run (nextTh)
endIf
junk = SetInterruptsTo (oldIntStat)
endMethod
---------- Thread . Sleep ----------
method Sleep ()
--
-- This method should only be invoked on the current thread. It
-- will set the status of the current thread to BLCOKED and will
-- will switch to executing another thread. It is assumed that
-- (1) Interrupts are disabled before calling this routine, and
-- (2) The current thread has been placed on some other wait
-- list (e.g., for a Semaphore) or else the thread will
-- never get scheduled again.
--
var nextTh: ptr to Thread
-- ASSERT:
if currentInterruptStatus != DISABLED
FatalError ("In Sleep, currentInterruptStatus != DISABLED")
endIf
-- ASSERT:
if self != currentThread
FatalError ("In Sleep, self != currentThread")
endIf
-- print ("Sleeping ")
-- print (name)
-- print ("\n")
status = BLOCKED
nextTh = readyList.Remove ()
if nextTh == null
FatalError ("Ready list should always contain the idle thread")
endIf
Run (nextTh)
endMethod
---------- Thread . CheckOverflow ----------
method CheckOverflow ()
--
-- This method checks to see if this thread has overflowed its
-- pre-alloted stack space. WARNING: the approach taken here is only
-- guaranteed to work "with high probability".
--
if systemStack[0] != STACK_SENTINEL
FatalError ("System stack overflow detected!")
elseIf systemStack[SYSTEM_STACK_SIZE-1] != STACK_SENTINEL
FatalError ("System stack underflow detected!")
endIf
endMethod
---------- Thread . Print ----------
method Print ()
--
-- Print this object.
--
var i: int
oldStatus: int
oldStatus = SetInterruptsTo (DISABLED)
print (" Thread \"")
print (name)
print ("\" (addr of Thread object: ")
printHex (self asInteger)
print (")\n")
print (" machine state:\n")
for i = 0 to 12
print (" r")
printInt (i+2)
print (": ")
printHex (regs[i])
print (" ")
printInt (regs[i])
print ("\n")
endFor
printHexVar (" stackTop", stackTop asInteger)
printHexVar (" stack starting addr", (& systemStack[0]) asInteger)
switch status
case JUST_CREATED:
print (" status = JUST_CREATED\n")
break
case READY:
print (" status = READY\n")
break
case RUNNING:
print (" status = RUNNING\n")
break
case BLOCKED:
print (" status = BLOCKED\n")
break
case UNUSED:
print (" status = UNUSED\n")
break
default:
FatalError ("Bad status in Thread")
endSwitch
oldStatus = SetInterruptsTo (oldStatus)
endMethod
endBehavior
endCode