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Kernel.c
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code Kernel
-- <PUT YOUR NAME HERE>
----------------------------- 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
FatalError = FatalError_ThreadVersion -- Use a routine which prints threadname
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".
--
-- It is allowable for nextThread to be currentThread.
--
var prevThread, th: ptr to Thread
prevThread = currentThread
prevThread.CheckOverflow ()
-- If the previous thread was using the USER registers, save them.
if prevThread.isUserThread
SaveUserRegs (&prevThread.userRegs[0])
endIf
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()
threadManager.FreeThread (th)
endWhile
-- If the new thread uses the USER registers, restore them.
if currentThread.isUserThread
RestoreUserRegs (¤tThread.userRegs[0])
currentThread.myProcess.addrSpace.SetToThisPageTable ()
endIf
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 (ThreadPrintShort)
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
FatalError ("This thread will never run again")
endFunction
----------------------------- FatalError_ThreadVersion -----------------------
function FatalError_ThreadVersion (errorMessage: ptr to array of char)
--
-- This function will print out the name of the current thread and
-- the given error message. Then it will call "RuntimeExit" to
-- shutdown the system.
--
var
junk: int
junk = SetInterruptsTo (DISABLED)
print ("\nFATAL ERROR")
if currentThread -- In case errors occur before thread initialization
print (" in ")
print (currentThread.name)
endIf
print (": \"")
print (errorMessage)
print ("\" -- TERMINATING!\n\n")
print ("(To find out where execution was when the problem arose, type 'st' at the emulator prompt.)\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
----------------------------- Semaphore ---------------------------------
behavior Semaphore
-- This class provides the following methods:
-- Up() ...also known as "V" or "Signal"...
-- Increment the semaphore count. Wake up a thread if
-- there are any waiting. This operation always executes
-- quickly and will not suspend the thread.
-- Down() ...also known as "P" or "Wait"...
-- Decrement the semaphore count. If the count would go
-- negative, wait for some other thread to do an Up()
-- first. Conceptually, the count will never go negative.
-- Init(initialCount)
-- Each semaphore must be initialized. Normally, you should
-- invoke this method, providing an 'initialCount' of zero.
-- If the semaphore is initialized with 0, then a Down()
-- operation before any Up() will wait for the first
-- Up(). If initialized with i, then it is as if i Up()
-- operations have been performed already.
--
-- NOTE: The user should never look at a semaphore's count since the value
-- retrieved may be out-of-date, due to other threads performing Up() or
-- Down() operations since the retrieval of the count.
---------- Semaphore . Init ----------
method Init (initialCount: int)
if initialCount < 0
FatalError ("Semaphore created with initialCount < 0")
endIf
count = initialCount
waitingThreads = new List [Thread]
endMethod
---------- Semaphore . Up ----------
method Up ()
var
oldIntStat: int
t: ptr to Thread
oldIntStat = SetInterruptsTo (DISABLED)
if count == 0x7fffffff
FatalError ("Semaphore count overflowed during 'Up' operation")
endIf
count = count + 1
if count <= 0
t = waitingThreads.Remove ()
t.status = READY
readyList.AddToEnd (t)
endIf
oldIntStat = SetInterruptsTo (oldIntStat)
endMethod
---------- Semaphore . Down ----------
method Down ()
var
oldIntStat: int
oldIntStat = SetInterruptsTo (DISABLED)
if count == 0x80000000
FatalError ("Semaphore count underflowed during 'Down' operation")
endIf
count = count - 1
if count < 0
waitingThreads.AddToEnd (currentThread)
currentThread.Sleep ()
endIf
oldIntStat = SetInterruptsTo (oldIntStat)
endMethod
endBehavior
----------------------------- Mutex ---------------------------------
behavior Mutex
-- This class provides the following methods:
-- Lock()
-- Acquire the mutex if free, otherwise wait until the mutex is
-- free and then get it.
-- Unlock()
-- Release the mutex. If other threads are waiting, then
-- wake up the oldest one and give it the lock.
-- Init()
-- Each mutex must be initialized.
-- IsHeldByCurrentThread()
-- Return TRUE iff the current (invoking) thread holds a lock
-- on the mutex.
----------- Mutex . Init -----------
method Init ()
waitingThreads = new List [Thread]
endMethod
----------- Mutex . Lock -----------
method Lock ()
var
oldIntStat: int
if heldBy == currentThread
FatalError ("Attempt to lock a mutex by a thread already holding it")
endIf
oldIntStat = SetInterruptsTo (DISABLED)
if !heldBy
heldBy = currentThread
else
waitingThreads.AddToEnd (currentThread)
currentThread.Sleep ()
endIf
oldIntStat = SetInterruptsTo (oldIntStat)
endMethod
----------- Mutex . Unlock -----------
method Unlock ()
var
oldIntStat: int
t: ptr to Thread
if heldBy != currentThread
FatalError ("Attempt to unlock a mutex by a thread not holding it")
endIf
oldIntStat = SetInterruptsTo (DISABLED)
t = waitingThreads.Remove ()
if t
t.status = READY
readyList.AddToEnd (t)
heldBy = t
else
heldBy = null
endIf
oldIntStat = SetInterruptsTo (oldIntStat)
endMethod
----------- Mutex . IsHeldByCurrentThread -----------
method IsHeldByCurrentThread () returns bool
return heldBy == currentThread
endMethod
endBehavior
----------------------------- Condition ---------------------------------
behavior Condition
-- This class is used to implement monitors. Each monitor will have a
-- mutex lock and one or more condition variables. The lock ensures that
-- only one process at a time may execute code in the monitor. Within the
-- monitor code, a thread can execute Wait() and Signal() operations
-- on the condition variables to make sure certain condions are met.
--
-- The condition variables here implement "Mesa-style" semantics, which
-- means that in the time between a Signal() operation and the awakening
-- and execution of the corrsponding waiting thread, other threads may
-- have snuck in and run. The waiting thread should always re-check the
-- data to ensure that the condition which was signalled is still true.
--
-- This class provides the following methods:
-- Wait(mutex)
-- This method assumes the mutex has alreasy been locked.
-- It unlocks it, and goes to sleep waiting for a signal on
-- this condition. When the signal is received, this method
-- re-awakens, re-locks the mutex, and returns.
-- Signal(mutex)
-- If there are any threads waiting on this condition, this
-- method will wake up the oldest and schedule it to run.
-- However, since this thread holds the mutex and never unlocks
-- it, the newly awakened thread will be forced to wait before
-- it can re-acquire the mutex and resume execution.
-- Broadcast(mutex)
-- This method is like Signal() except that it wakes up all
-- threads waiting on this condition, not just the next one.
-- Init()
-- Each condition must be initialized.
---------- Condition . Init ----------
method Init ()
waitingThreads = new List [Thread]
endMethod
---------- Condition . Wait ----------
method Wait (mutex: ptr to Mutex)
var
oldIntStat: int
if ! mutex.IsHeldByCurrentThread ()
FatalError ("Attempt to wait on condition when mutex is not held")
endIf
oldIntStat = SetInterruptsTo (DISABLED)
mutex.Unlock ()
waitingThreads.AddToEnd (currentThread)
currentThread.Sleep ()
mutex.Lock ()
oldIntStat = SetInterruptsTo (oldIntStat)
endMethod
---------- Condition . Signal ----------
method Signal (mutex: ptr to Mutex)
var
oldIntStat: int
t: ptr to Thread
if ! mutex.IsHeldByCurrentThread ()
FatalError ("Attempt to signal a condition when mutex is not held")
endIf
oldIntStat = SetInterruptsTo (DISABLED)
t = waitingThreads.Remove ()
if t
t.status = READY
readyList.AddToEnd (t)
endIf
oldIntStat = SetInterruptsTo (oldIntStat)
endMethod
---------- Condition . Broadcast ----------
method Broadcast (mutex: ptr to Mutex)
var
oldIntStat: int
t: ptr to Thread
if ! mutex.IsHeldByCurrentThread ()
FatalError ("Attempt to broadcast a condition when lock is not held")
endIf
oldIntStat = SetInterruptsTo (DISABLED)
while true
t = waitingThreads.Remove ()
if t == null
break
endIf
t.status = READY
readyList.AddToEnd (t)
endWhile
oldIntStat = SetInterruptsTo (oldIntStat)
endMethod
endBehavior
----------------------------- 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 }
isUserThread = false
userRegs = new array of int { 15 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
print (" is user thread: ")
printBool (isUserThread)
nl ()
print (" user registers:\n")
for i = 0 to 14
print (" r")
printInt (i+1)
print (": ")
printHex (userRegs[i])
print (" ")
printInt (userRegs[i])
print ("\n")
endFor
oldStatus = SetInterruptsTo (oldStatus)
endMethod
endBehavior
----------------------------- ThreadPrintShort ---------------------------------
function ThreadPrintShort (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 distinguishing Threads when the name is not helpful).
--
var
oldStatus: int = SetInterruptsTo (DISABLED)
if !t
print ("NULL\n")
return
endIf
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
----------------------------- ThreadManager ---------------------------------
behavior ThreadManager
---------- ThreadManager . Init ----------
method Init ()
--
-- This method is called once at kernel startup time to initialize
-- the one and only "ThreadManager" object.
--
print ("Initializing Thread Manager...\n")
-- NOT IMPLEMENTED
endMethod
---------- ThreadManager . Print ----------
method Print ()
--
-- Print each thread. Since we look at the freeList, this
-- routine disables interrupts so the printout will be a
-- consistent snapshot of things.
--
var i, oldStatus: int
oldStatus = SetInterruptsTo (DISABLED)
print ("Here is the thread table...\n")
for i = 0 to MAX_NUMBER_OF_PROCESSES-1
print (" ")
printInt (i)
print (":")
ThreadPrintShort (&threadTable[i])
endFor
print ("Here is the FREE list of Threads:\n ")
freeList.ApplyToEach (PrintObjectAddr)
nl ()
oldStatus = SetInterruptsTo (oldStatus)
endMethod
---------- ThreadManager . GetANewThread ----------
method GetANewThread () returns ptr to Thread
--
-- This method returns a new Thread; it will wait
-- until one is available.
--
-- NOT IMPLEMENTED
return null
endMethod
---------- ThreadManager . FreeThread ----------
method FreeThread (th: ptr to Thread)
--
-- This method is passed a ptr to a Thread; It moves it
-- to the FREE list.
--
-- NOT IMPLEMENTED
endMethod
endBehavior
-------------------------- ProcessControlBlock ------------------------------
behavior ProcessControlBlock
---------- ProcessControlBlock . Init ----------
--
-- This method is called once for every PCB at startup time.
--
method Init ()
pid = -1
status = FREE
addrSpace = new AddrSpace
addrSpace.Init ()
-- Uncomment this code later...
/*
fileDescriptor = new array of ptr to OpenFile
{ MAX_FILES_PER_PROCESS of null }
*/
endMethod
---------- ProcessControlBlock . Print ----------
method Print ()
--
-- Print this ProcessControlBlock using several lines.
--
-- var i: int
self.PrintShort ()
addrSpace.Print ()
print (" myThread = ")
ThreadPrintShort (myThread)
-- Uncomment this code later...
/*
print (" File Descriptors:\n")
for i = 0 to MAX_FILES_PER_PROCESS-1
if fileDescriptor[i]
fileDescriptor[i].Print ()
endIf
endFor
*/
nl ()
endMethod
---------- ProcessControlBlock . PrintShort ----------
method PrintShort ()
--
-- Print this ProcessControlBlock on one line.
--
print (" ProcessControlBlock (addr=")
printHex (self asInteger)
print (") pid=")
printInt (pid)
print (", status=")
if status == ACTIVE
print ("ACTIVE")
elseIf status == ZOMBIE
print ("ZOMBIE")
elseIf status == FREE
print ("FREE")
else
FatalError ("Bad status in ProcessControlBlock")
endIf
print (", parentsPid=")
printInt (parentsPid)
print (", exitStatus=")
printInt (exitStatus)
nl ()
endMethod
endBehavior
----------------------------- ProcessManager ---------------------------------
behavior ProcessManager
---------- ProcessManager . Init ----------
method Init ()
--
-- This method is called once at kernel startup time to initialize
-- the one and only "processManager" object.
--
-- NOT IMPLEMENTED
endMethod
---------- ProcessManager . Print ----------
method Print ()
--
-- Print all processes. Since we look at the freeList, this
-- routine disables interrupts so the printout will be a
-- consistent snapshot of things.
--
var i, oldStatus: int
oldStatus = SetInterruptsTo (DISABLED)
print ("Here is the process table...\n")
for i = 0 to MAX_NUMBER_OF_PROCESSES-1
print (" ")
printInt (i)
print (":")
processTable[i].Print ()
endFor
print ("Here is the FREE list of ProcessControlBlocks:\n ")
freeList.ApplyToEach (PrintObjectAddr)
nl ()
oldStatus = SetInterruptsTo (oldStatus)
endMethod
---------- ProcessManager . PrintShort ----------
method PrintShort ()
--
-- Print all processes. Since we look at the freeList, this
-- routine disables interrupts so the printout will be a
-- consistent snapshot of things.
--
var i, oldStatus: int
oldStatus = SetInterruptsTo (DISABLED)
print ("Here is the process table...\n")
for i = 0 to MAX_NUMBER_OF_PROCESSES-1
print (" ")
printInt (i)
processTable[i].PrintShort ()
endFor
print ("Here is the FREE list of ProcessControlBlocks:\n ")
freeList.ApplyToEach (PrintObjectAddr)
nl ()
oldStatus = SetInterruptsTo (oldStatus)
endMethod
---------- ProcessManager . GetANewProcess ----------
method GetANewProcess () returns ptr to ProcessControlBlock
--
-- This method returns a new ProcessControlBlock; it will wait
-- until one is available.
--
-- NOT IMPLEMENTED
return null
endMethod
---------- ProcessManager . FreeProcess ----------
method FreeProcess (p: ptr to ProcessControlBlock)
--
-- This method is passed a ptr to a Process; It moves it
-- to the FREE list.
--
-- NOT IMPLEMENTED
endMethod
endBehavior
----------------------------- PrintObjectAddr ---------------------------------
function PrintObjectAddr (p: ptr to Object)
--
-- Print the address of the given object.
--
printHex (p asInteger)
printChar (' ')
endFunction
----------------------------- ProcessFinish --------------------------
function ProcessFinish (exitStatus: int)
--
-- This routine is called when a process is to be terminated. It will
-- free the resources held by this process and will terminate the
-- current thread.
--
FatalError ("ProcessFinish is not implemented")
endFunction
----------------------------- FrameManager ---------------------------------
behavior FrameManager
---------- FrameManager . Init ----------
method Init ()
--
-- This method is called once at kernel startup time to initialize
-- the one and only "frameManager" object.
--
var i: int
print ("Initializing Frame Manager...\n")
framesInUse = new BitMap
framesInUse.Init (NUMBER_OF_PHYSICAL_PAGE_FRAMES)
numberFreeFrames = NUMBER_OF_PHYSICAL_PAGE_FRAMES
frameManagerLock = new Mutex
frameManagerLock.Init ()
newFramesAvailable = new Condition
newFramesAvailable.Init ()
-- Check that the area to be used for paging contains zeros.
-- The BLITZ emulator will initialize physical memory to zero, so
-- if by chance the size of the kernel has gotten so large that
-- it runs into the area reserved for pages, we will detect it.
-- Note: this test is not 100%, but is included nonetheless.
for i = PHYSICAL_ADDRESS_OF_FIRST_PAGE_FRAME
to PHYSICAL_ADDRESS_OF_FIRST_PAGE_FRAME+300
by 4
if 0 != *(i asPtrTo int)
FatalError ("Kernel code size appears to have grown too large and is overflowing into the frame region")
endIf
endFor
endMethod
---------- FrameManager . Print ----------
method Print ()
--
-- Print which frames are allocated and how many are free.
--
frameManagerLock.Lock ()
print ("FRAME MANAGER:\n")
printIntVar (" numberFreeFrames", numberFreeFrames)
print (" Here are the frames in use: \n ")
framesInUse.Print ()
frameManagerLock.Unlock ()
endMethod
---------- FrameManager . GetAFrame ----------
method GetAFrame () returns int
--
-- Allocate a single frame and return its physical address. If no frames
-- are currently available, wait until the request can be completed.
--
var f, frameAddr: int
-- Acquire exclusive access to the frameManager data structure...
frameManagerLock.Lock ()
-- Wait until we have enough free frames to entirely satisfy the request...
while numberFreeFrames < 1
newFramesAvailable.Wait (&frameManagerLock)
endWhile
-- Find a free frame and allocate it...
f = framesInUse.FindZeroAndSet ()
numberFreeFrames = numberFreeFrames - 1
-- Unlock...
frameManagerLock.Unlock ()
-- Compute and return the physical address of the frame...
frameAddr = PHYSICAL_ADDRESS_OF_FIRST_PAGE_FRAME + (f * PAGE_SIZE)
-- printHexVar ("GetAFrame returning frameAddr", frameAddr)
return frameAddr
endMethod
---------- FrameManager . GetNewFrames ----------
method GetNewFrames (aPageTable: ptr to AddrSpace, numFramesNeeded: int)
-- NOT IMPLEMENTED
endMethod
---------- FrameManager . ReturnAllFrames ----------
method ReturnAllFrames (aPageTable: ptr to AddrSpace)
-- NOT IMPLEMENTED
endMethod
endBehavior
----------------------------- AddrSpace ---------------------------------
behavior AddrSpace
---------- AddrSpace . Init ----------
method Init ()
--
-- Initialize this object.
--
numberOfPages = 0
pageTable = new array of int { MAX_PAGES_PER_VIRT_SPACE of 0x00000003 }
endMethod
---------- AddrSpace . Print ----------
method Print ()
--
-- Print this object.
--
var i: int
print (" addr entry Logical Physical Undefined Bits Dirty Referenced Writeable Valid\n")
print (" ========== ========== ========== ========== ============== ===== ========== ========= =====\n")
for i = 0 to numberOfPages-1
print (" ")
printHex ((&pageTable[i]) asInteger)
print (": ")
printHex (pageTable[i])
print (" ")
printHex (i * PAGE_SIZE) -- Logical address
print (" ")
printHex (self.ExtractFrameAddr (i)) -- Physical address
print (" ")
if self.ExtractUndefinedBits (i) != 0
printHex (self.ExtractUndefinedBits (i))
else
print (" ")
endIf
print (" ")
if self.IsDirty (i)
print ("YES")
else
print (" ")
endIf
print (" ")
if self.IsReferenced (i)
print ("YES")
else
print (" ")
endIf
print (" ")
if self.IsWritable (i)
print ("YES")
else
print (" ")
endIf
print (" ")
if self.IsValid (i)
print ("YES")
else
print (" ")
endIf
nl ()
endFor
endMethod
---------- AddrSpace . ExtractFrameAddr ----------
method ExtractFrameAddr (entry: int) returns int
--
-- Return the physical address of the frame in the selected page
-- table entry.
--
return (pageTable[entry] & 0xffffe000)
endMethod
---------- AddrSpace . ExtractUndefinedBits ----------
method ExtractUndefinedBits (entry: int) returns int
--
-- Return the undefined bits in the selected page table entry.
--
return (pageTable[entry] & 0x00001ff0)
endMethod
---------- AddrSpace . SetFrameAddr ----------
method SetFrameAddr (entry: int, frameAddr: int)
--
-- Set the physical address of the frame in the selected page
-- table entry to the value of the argument "frameAddr".
--
pageTable[entry] = (pageTable[entry] & 0x00001fff) | frameAddr
endMethod
---------- AddrSpace . IsDirty ----------
method IsDirty (entry: int) returns bool
--
-- Return true if the selected page table entry is marked "dirty".
--
return (pageTable[entry] & 0x00000008) != 0
endMethod
---------- AddrSpace . IsReferenced ----------
method IsReferenced (entry: int) returns bool
--
-- Return true if the selected page table entry is marked "referenced".
--
return (pageTable[entry] & 0x00000004) != 0
endMethod
---------- AddrSpace . IsWritable ----------
method IsWritable (entry: int) returns bool
--
-- Return true if the selected page table entry is marked "writable".
--
return (pageTable[entry] & 0x00000002) != 0
endMethod
---------- AddrSpace . IsValid ----------
method IsValid (entry: int) returns bool
--
-- Return true if the selected page table entry is marked "valid".
--
return (pageTable[entry] & 0x00000001) != 0
endMethod
---------- AddrSpace . SetDirty ----------
method SetDirty (entry: int)
--
-- Set the selected page table entry's "dirty" bit to 1.
--
pageTable[entry] = pageTable[entry] | 0x00000008
endMethod
---------- AddrSpace . SetReferenced ----------
method SetReferenced (entry: int)
--
-- Set the selected page table entry's "referenced" bit to 1.
--
pageTable[entry] = pageTable[entry] | 0x00000004
endMethod
---------- AddrSpace . SetWritable ----------
method SetWritable (entry: int)
--
-- Set the selected page table entry's "writable" bit to 1.
--
pageTable[entry] = pageTable[entry] | 0x00000002
endMethod
---------- AddrSpace . SetValid ----------
method SetValid (entry: int)
--
-- Set the selected page table entry's "valid" bit to 1.
--
pageTable[entry] = pageTable[entry] | 0x00000001
endMethod
---------- AddrSpace . ClearDirty ----------
method ClearDirty (entry: int)
--
-- Clear the selected page table entry's "dirty" bit.
--
pageTable[entry] = pageTable[entry] & ! 0x00000008
endMethod
---------- AddrSpace . ClearReferenced ----------
method ClearReferenced (entry: int)
--
-- Clear the selected page table entry's "referenced" bit.
--
pageTable[entry] = pageTable[entry] & ! 0x00000004
endMethod
---------- AddrSpace . ClearWritable ----------
method ClearWritable (entry: int)
--
-- Clear the selected page table entry's "writable" bit.
--
pageTable[entry] = pageTable[entry] & ! 0x00000002
endMethod
---------- AddrSpace . ClearValid ----------
method ClearValid (entry: int)
--
-- Clear the selected page table entry's "valid" bit.
--
pageTable[entry] = pageTable[entry] & ! 0x00000001
endMethod
---------- AddrSpace . SetToThisPageTable ----------
method SetToThisPageTable ()
--
-- This method sets the page table registers in the CPU to
-- point to this page table. Later, when paging is enabled,
-- this will become the active virtual address space.
--
LoadPageTableRegs ((& pageTable[0]) asInteger, numberOfPages*4)
endMethod
---------- AddrSpace . CopyBytesFromVirtual ----------
method CopyBytesFromVirtual (kernelAddr, virtAddr, numBytes: int)
returns int
--
-- This method copies data from a user's virtual address space
-- to somewhere in the kernel space. We assume that the
-- pages of the virtual address space are resident in
-- physical page frames. This routine returns the number of bytes
-- that were copied; if there was any problem with the virtual
-- addressed data, it returns -1.
--
var copiedSoFar, virtPage, offset, fromAddr: int
-- print ("CopyBytesFromVirtual called...\n")
-- printHexVar (" kernelAddr", kernelAddr)
-- printHexVar (" virtAddr", virtAddr)
-- printIntVar (" numBytes", numBytes)
if numBytes == 0
return 0
elseIf numBytes < 0
return -1
endIf
virtPage = virtAddr / PAGE_SIZE
offset = virtAddr % PAGE_SIZE
-- printHexVar (" virtPage", virtPage)
-- printHexVar (" offset", offset)
while true
if virtPage >= numberOfPages
print (" Virtual page number is too large!!!\n")
return -1
endIf
if ! self.IsValid (virtPage)
print (" Virtual page is not marked VALID!!!\n")
return -1
endIf
fromAddr = self.ExtractFrameAddr (virtPage) + offset
-- printHexVar (" Copying bytes from physcial addr", fromAddr)
while offset < PAGE_SIZE
-- printHexVar (" Copying a byte to physcial addr", kernelAddr)
-- printChar (* (fromAddr asPtrTo char))
* (kernelAddr asPtrTo char) = * (fromAddr asPtrTo char)
offset = offset + 1
kernelAddr = kernelAddr + 1
fromAddr = fromAddr + 1
copiedSoFar = copiedSoFar + 1
if copiedSoFar == numBytes
return copiedSoFar
endIf
endWhile
virtPage = virtPage + 1
offset = 0
endWhile
endMethod
---------- AddrSpace . CopyBytesToVirtual ----------
method CopyBytesToVirtual (virtAddr, kernelAddr, numBytes: int)
returns int
--
-- This method copies data from the kernel's address space to
-- somewhere in the virtual address space. We assume that the
-- pages of the virtual address space are resident in physical
-- page frames. This routine returns the number of bytes
-- that were copied; if there was any problem with the virtual
-- addressed data, it returns -1.
--
var copiedSoFar, virtPage, offset, destAddr: int
if numBytes == 0
return 0
elseIf numBytes < 0
return -1
endIf
virtPage = virtAddr / PAGE_SIZE
offset = virtAddr % PAGE_SIZE
while true
if (virtPage >= numberOfPages) ||
(! self.IsValid (virtPage)) ||
(! self.IsWritable (virtPage))
return -1
endIf
destAddr = self.ExtractFrameAddr (virtPage) + offset
while offset < PAGE_SIZE
* (destAddr asPtrTo char) = * (kernelAddr asPtrTo char)
offset = offset + 1
kernelAddr = kernelAddr + 1
destAddr = destAddr + 1
copiedSoFar = copiedSoFar + 1
if copiedSoFar == numBytes
return copiedSoFar
endIf
endWhile
virtPage = virtPage + 1
offset = 0
endWhile
endMethod
---------- AddrSpace . GetStringFromVirtual ----------
method GetStringFromVirtual (kernelAddr: String, virtAddr, maxSize: int) returns int
--
-- This method is used to copy a String from virtual space into
-- a given physical address in the kernel. The "kernelAddr" should be
-- a pointer to an "array of char" in the kernel's code. This method
-- copies up to "maxSize" characters from approriate page frame to this
-- to the target array in the kernel.
--
-- Note: This method resets the "arraySize" word in the target. It is
-- assumed that the target array has enough space; no checking is done.
-- The caller should supply a "maxSize" telling how many characters may
-- be safely copied.
--
-- If there are problems, then -1 is returned. Possible problems:
-- The source array has more than "maxSize" elements
-- The source page is invalid or out of range
-- If all okay, then the number of characters copied is returned.
--
var sourceSize: int
-- print ("GetStringFromVirtual called...\n")
-- printHexVar (" kernelAddr", kernelAddr asInteger)
-- printHexVar (" virtAddr", virtAddr)
-- printIntVar (" maxSize", maxSize)
-- Begin by fetching the source size
if self.CopyBytesFromVirtual ((&sourceSize) asInteger,
virtAddr,
4) < 4
return -1
endIf
-- printIntVar (" sourceSize", sourceSize)
-- Make sure the source size is okay
if sourceSize > maxSize
return -1
endIf
-- Change the size of the destination array
* (kernelAddr asPtrTo int) = sourceSize
-- Next, get the characters
return self.CopyBytesFromVirtual (kernelAddr asInteger + 4,
virtAddr + 4,
sourceSize)
endMethod
endBehavior
----------------------------- 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
----------------------------- DiskInterruptHandler --------------------------
function DiskInterruptHandler ()
--
-- This routine is called when a disk interrupt occurs. It will
-- signal the "semToSignalOnCompletion" Semaphore and return to
-- the interrupted thread.
--
-- This is an interrupt handler. As such, interrupts will be DISABLED
-- for the duration of its execution.
--
-- Uncomment this code later...
FatalError ("DISK INTERRUPTS NOT EXPECTED IN PROJECT 4")
/*
currentInterruptStatus = DISABLED
-- print ("DiskInterruptHandler invoked!\n")
if diskDriver.semToSignalOnCompletion
diskDriver.semToSignalOnCompletion.Up()
endIf
*/
endFunction
----------------------------- SerialInterruptHandler --------------------------
function SerialInterruptHandler ()
--
-- This routine is called when a serial interrupt occurs. It will
-- signal the "semToSignalOnCompletion" Semaphore and return to
-- the interrupted thread.
--
-- This is an interrupt handler. As such, interrupts will be DISABLED
-- for the duration of its execution.
--
currentInterruptStatus = DISABLED
-- NOT IMPLEMENTED
endFunction
----------------------------- IllegalInstructionHandler --------------------------
function IllegalInstructionHandler ()
--
-- This routine is called when an IllegalInstruction exception occurs. Upon entry,
-- interrupts are DISABLED. We should not return to the code that had
-- the exception.
--
currentInterruptStatus = DISABLED
ErrorInUserProcess ("An IllegalInstruction exception has occured while in user mode")
endFunction
----------------------------- ArithmeticExceptionHandler --------------------------
function ArithmeticExceptionHandler ()
--
-- This routine is called when an ArithmeticException occurs. Upon entry,
-- interrupts are DISABLED. We should not return to the code that had
-- the exception.
--
currentInterruptStatus = DISABLED
ErrorInUserProcess ("An ArithmeticException exception has occured while in user mode")
endFunction
----------------------------- AddressExceptionHandler --------------------------
function AddressExceptionHandler ()
--
-- This routine is called when an AddressException occurs. Upon entry,
-- interrupts are DISABLED. We should not return to the code that had
-- the exception.
--
currentInterruptStatus = DISABLED
ErrorInUserProcess ("An AddressException exception has occured while in user mode")
endFunction
----------------------------- PageInvalidExceptionHandler --------------------------
function PageInvalidExceptionHandler ()
--
-- This routine is called when a PageInvalidException occurs. Upon entry,
-- interrupts are DISABLED. For now, we simply print a message and abort
-- the thread.
--
currentInterruptStatus = DISABLED
ErrorInUserProcess ("A PageInvalidException exception has occured while in user mode")
endFunction
----------------------------- PageReadonlyExceptionHandler --------------------------
function PageReadonlyExceptionHandler ()
--
-- This routine is called when a PageReadonlyException occurs. Upon entry,
-- interrupts are DISABLED. For now, we simply print a message and abort
-- the thread.
--
currentInterruptStatus = DISABLED
ErrorInUserProcess ("A PageReadonlyException exception has occured while in user mode")
endFunction
----------------------------- PrivilegedInstructionHandler --------------------------
function PrivilegedInstructionHandler ()
--
-- This routine is called when a PrivilegedInstruction exception occurs. Upon entry,
-- interrupts are DISABLED. We should not return to the code that had
-- the exception.
--
currentInterruptStatus = DISABLED
ErrorInUserProcess ("A PrivilegedInstruction exception has occured while in user mode")
endFunction
----------------------------- AlignmentExceptionHandler --------------------------
function AlignmentExceptionHandler ()
--
-- This routine is called when an AlignmentException occurs. Upon entry,
-- interrupts are DISABLED. We should not return to the code that had
-- the exception.
--
currentInterruptStatus = DISABLED
ErrorInUserProcess ("An AlignmentException exception has occured while in user mode")
endFunction
----------------------------- ErrorInUserProcess --------------------------
function ErrorInUserProcess (errorMessage: String)
--
-- This routine is called when an error has occurred in a user-level
-- process. It prints the error message and terminates the process.
--
print ("\n********** ")
print (errorMessage)
print (" **********\n\n")
-- Print some information about the offending process...
if currentThread.myProcess
currentThread.myProcess.Print ()
else
print (" ERROR: currentThread.myProcess is null\n\n")
endIf
currentThread.Print ()
-- Uncomment the following for even more information...
-- threadManager.Print ()
-- processManager.Print ()
ProcessFinish (-1)
endFunction
----------------------------- SyscallTrapHandler --------------------------
function SyscallTrapHandler (syscallCodeNum, arg1, arg2, arg3, arg4: int) returns int
--
-- This routine is called when a syscall trap occurs. Upon entry, interrupts
-- will be DISABLED, paging is disabled, and we will be running in System mode.
-- Upon return, execution will return to the user mode portion of this
-- thread, which will have had interrupts ENABLED.
--
currentInterruptStatus = DISABLED
/*****
print ("Within SyscallTrapHandler: syscallCodeNum=")
printInt (syscallCodeNum)
print (", arg1=")
printInt (arg1)
print (", arg2=")
printInt (arg2)
print (", arg3=")
printInt (arg3)
print (", arg4=")
printInt (arg4)
nl ()
*****/
switch syscallCodeNum
case SYSCALL_FORK:
return Handle_Sys_Fork ()
case SYSCALL_YIELD:
Handle_Sys_Yield ()
return 0
case SYSCALL_EXEC:
return Handle_Sys_Exec (arg1 asPtrTo array of char)
case SYSCALL_JOIN:
return Handle_Sys_Join (arg1)
case SYSCALL_EXIT:
Handle_Sys_Exit (arg1)
return 0
case SYSCALL_CREATE:
return Handle_Sys_Create (arg1 asPtrTo array of char)
case SYSCALL_OPEN:
return Handle_Sys_Open (arg1 asPtrTo array of char)
case SYSCALL_READ:
return Handle_Sys_Read (arg1, arg2 asPtrTo char, arg3)
case SYSCALL_WRITE:
return Handle_Sys_Write (arg1, arg2 asPtrTo char, arg3)
case SYSCALL_SEEK:
return Handle_Sys_Seek (arg1, arg2)
case SYSCALL_CLOSE:
Handle_Sys_Close (arg1)
return 0
case SYSCALL_SHUTDOWN:
Handle_Sys_Shutdown ()
return 0
default:
print ("Syscall code = ")
printInt (syscallCodeNum)
nl ()
FatalError ("Unknown syscall code from user thread")
endSwitch
return 0
endFunction
----------------------------- Handle_Sys_Exit ---------------------------------
function Handle_Sys_Exit (returnStatus: int)
-- NOT IMPLEMENTED
endFunction
----------------------------- Handle_Sys_Shutdown ---------------------------------
function Handle_Sys_Shutdown ()
-- NOT IMPLEMENTED
endFunction
----------------------------- Handle_Sys_Yield ---------------------------------
function Handle_Sys_Yield ()
-- NOT IMPLEMENTED
endFunction
----------------------------- Handle_Sys_Fork ---------------------------------
function Handle_Sys_Fork () returns int
-- NOT IMPLEMENTED
return 0
endFunction
----------------------------- Handle_Sys_Join ---------------------------------
function Handle_Sys_Join (processID: int) returns int
-- NOT IMPLEMENTED
return 0
endFunction
----------------------------- Handle_Sys_Exec ---------------------------------
function Handle_Sys_Exec (filename: ptr to array of char) returns int
-- NOT IMPLEMENTED
return 0
endFunction
----------------------------- Handle_Sys_Create ---------------------------------
function Handle_Sys_Create (filename: ptr to array of char) returns int
-- NOT IMPLEMENTED
return 0
endFunction
----------------------------- Handle_Sys_Open ---------------------------------
function Handle_Sys_Open (filename: ptr to array of char) returns int
-- NOT IMPLEMENTED
return 0
endFunction
----------------------------- Handle_Sys_Read ---------------------------------
function Handle_Sys_Read (fileDesc: int, buffer: ptr to char, sizeInBytes: int) returns int
-- NOT IMPLEMENTED
return 0
endFunction
----------------------------- Handle_Sys_Write ---------------------------------
function Handle_Sys_Write (fileDesc: int, buffer: ptr to char, sizeInBytes: int) returns int
-- NOT IMPLEMENTED
return 0
endFunction
----------------------------- Handle_Sys_Seek ---------------------------------
function Handle_Sys_Seek (fileDesc: int, newCurrentPos: int) returns int
-- NOT IMPLEMENTED
return 0
endFunction
----------------------------- Handle_Sys_Close ---------------------------------
function Handle_Sys_Close (fileDesc: int)
-- NOT IMPLEMENTED
endFunction
endCode