--- /dev/null
+/*
+ * Kernel threads
+ * Copyright (c) 2001,2003 David H. Hovemeyer <daveho@cs.umd.edu>
+ * $Revision: 1.4 $
+ *
+ * This is free software. You are permitted to use,
+ * redistribute, and modify it as specified in the file "COPYING".
+ */
+
+#include <geekos/kassert.h>
+#include <geekos/defs.h>
+#include <geekos/screen.h>
+#include <geekos/int.h>
+#include <geekos/mem.h>
+#include <geekos/symbol.h>
+#include <geekos/string.h>
+#include <geekos/kthread.h>
+#include <geekos/malloc.h>
+#include <geekos/serial.h>
+#include <geekos/debug.h>
+
+/* ----------------------------------------------------------------------
+ * Private data
+ * ---------------------------------------------------------------------- */
+
+/*
+ * List of all threads in the system.
+ */
+static struct All_Thread_List s_allThreadList;
+
+/*
+ * Queue of runnable threads.
+ */
+static struct Thread_Queue s_runQueue;
+
+/*
+ * Current thread.
+ */
+struct Kernel_Thread* g_currentThread;
+
+/*
+ * Boolean flag indicating that we need to choose a new runnable thread.
+ * It is checked by the interrupt return code (Handle_Interrupt,
+ * in lowlevel.asm) before returning from an interrupt.
+ */
+int g_needReschedule;
+
+/*
+ * Boolean flag indicating that preemption is disabled.
+ * When set, external interrupts (such as the timer tick)
+ * will not cause a new thread to be selected.
+ */
+volatile int g_preemptionDisabled;
+
+/*
+ * Queue of finished threads needing disposal,
+ * and a wait queue used for communication between exited threads
+ * and the reaper thread.
+ */
+static struct Thread_Queue s_graveyardQueue;
+static struct Thread_Queue s_reaperWaitQueue;
+
+/*
+ * Counter for keys that access thread-local data, and an array
+ * of destructors for freeing that data when the thread dies. This is
+ * based on POSIX threads' thread-specific data functionality.
+ */
+static unsigned int s_tlocalKeyCounter = 0;
+static tlocal_destructor_t s_tlocalDestructors[MAX_TLOCAL_KEYS];
+
+/* ----------------------------------------------------------------------
+ * Private functions
+ * ---------------------------------------------------------------------- */
+
+/*
+ * Initialize a new Kernel_Thread.
+ */
+static void Init_Thread(struct Kernel_Thread* kthread, void* stackPage,
+ int priority, bool detached)
+{
+ static int nextFreePid = 1;
+
+ struct Kernel_Thread* owner = detached ? (struct Kernel_Thread*)0 : g_currentThread;
+
+ memset(kthread, '\0', sizeof(*kthread));
+ kthread->stackPage = stackPage;
+ kthread->esp = ((ulong_t) kthread->stackPage) + PAGE_SIZE;
+ kthread->numTicks = 0;
+ kthread->priority = priority;
+ kthread->userContext = 0;
+ kthread->owner = owner;
+
+ /*
+ * The thread has an implicit self-reference.
+ * If the thread is not detached, then its owner
+ * also has a reference to it.
+ */
+ kthread->refCount = detached ? 1 : 2;
+
+ kthread->alive = true;
+ Clear_Thread_Queue(&kthread->joinQueue);
+ kthread->pid = nextFreePid++;
+
+}
+
+/*
+ * Create a new raw thread object.
+ * Returns a null pointer if there isn't enough memory.
+ */
+static struct Kernel_Thread* Create_Thread(int priority, bool detached)
+{
+ struct Kernel_Thread* kthread;
+ void* stackPage = 0;
+
+ /*
+ * For now, just allocate one page each for the thread context
+ * object and the thread's stack.
+ */
+ kthread = Alloc_Page();
+ if (kthread != 0)
+ stackPage = Alloc_Page();
+
+ /* Make sure that the memory allocations succeeded. */
+ if (kthread == 0)
+ return 0;
+ if (stackPage == 0) {
+ Free_Page(kthread);
+ return 0;
+ }
+
+ /*Print("New thread @ %x, stack @ %x\n", kthread, stackPage); */
+
+ /*
+ * Initialize the stack pointer of the new thread
+ * and accounting info
+ */
+ Init_Thread(kthread, stackPage, priority, detached);
+
+ /* Add to the list of all threads in the system. */
+ Add_To_Back_Of_All_Thread_List(&s_allThreadList, kthread);
+
+ return kthread;
+}
+
+/*
+ * Push a dword value on the stack of given thread.
+ * We use this to set up some context for the thread before
+ * we make it runnable.
+ */
+static __inline__ void Push(struct Kernel_Thread* kthread, ulong_t value)
+{
+ kthread->esp -= 4;
+ *((ulong_t *) kthread->esp) = value;
+}
+
+/*
+ * Destroy given thread.
+ * This function should perform all cleanup needed to
+ * reclaim the resources used by a thread.
+ * Called with interrupts enabled.
+ */
+static void Destroy_Thread(struct Kernel_Thread* kthread)
+{
+
+ /* Dispose of the thread's memory. */
+ Disable_Interrupts();
+ Free_Page(kthread->stackPage);
+ Free_Page(kthread);
+
+ /* Remove from list of all threads */
+ Remove_From_All_Thread_List(&s_allThreadList, kthread);
+
+ Enable_Interrupts();
+
+}
+
+/*
+ * Hand given thread to the reaper for destruction.
+ * Must be called with interrupts disabled!
+ */
+static void Reap_Thread(struct Kernel_Thread* kthread)
+{
+ KASSERT(!Interrupts_Enabled());
+ Enqueue_Thread(&s_graveyardQueue, kthread);
+ Wake_Up(&s_reaperWaitQueue);
+}
+
+/*
+ * Called when a reference to the thread is broken.
+ */
+static void Detach_Thread(struct Kernel_Thread* kthread)
+{
+ KASSERT(!Interrupts_Enabled());
+ KASSERT(kthread->refCount > 0);
+
+ --kthread->refCount;
+ if (kthread->refCount == 0) {
+ Reap_Thread(kthread);
+ }
+}
+
+/*
+ * This function performs any needed initialization before
+ * a thread start function is executed. Currently we just use
+ * it to enable interrupts (since Schedule() always activates
+ * a thread with interrupts disabled).
+ */
+static void Launch_Thread(void)
+{
+ Enable_Interrupts();
+}
+
+/*
+ * Push initial values for general purpose registers.
+ */
+static void Push_General_Registers(struct Kernel_Thread* kthread)
+{
+ /*
+ * Push initial values for saved general-purpose registers.
+ * (The actual values are not important.)
+ */
+ Push(kthread, 0); /* eax */
+ Push(kthread, 0); /* ebx */
+ Push(kthread, 0); /* edx */
+ Push(kthread, 0); /* edx */
+ Push(kthread, 0); /* esi */
+ Push(kthread, 0); /* edi */
+ Push(kthread, 0); /* ebp */
+}
+
+/*
+ * Shutdown a kernel thread.
+ * This is called if a kernel thread exits by falling off
+ * the end of its start function.
+ */
+static void Shutdown_Thread(void)
+{
+ Exit(0);
+}
+
+/*
+ * Set up the initial context for a kernel-mode-only thread.
+ */
+static void Setup_Kernel_Thread(
+ struct Kernel_Thread* kthread,
+ Thread_Start_Func startFunc,
+ ulong_t arg)
+{
+ /*
+ * Push the argument to the thread start function, and the
+ * return address (the Shutdown_Thread function, so the thread will
+ * go away cleanly when the start function returns).
+ */
+ Push(kthread, arg);
+ Push(kthread, (ulong_t) &Shutdown_Thread);
+
+ /* Push the address of the start function. */
+ Push(kthread, (ulong_t) startFunc);
+
+ /*
+ * To make the thread schedulable, we need to make it look
+ * like it was suspended by an interrupt. This means pushing
+ * an "eflags, cs, eip" sequence onto the stack,
+ * as well as int num, error code, saved registers, etc.
+ */
+
+ /*
+ * The EFLAGS register will have all bits clear.
+ * The important constraint is that we want to have the IF
+ * bit clear, so that interrupts are disabled when the
+ * thread starts.
+ */
+ Push(kthread, 0UL); /* EFLAGS */
+
+ /*
+ * As the "return address" specifying where the new thread will
+ * start executing, use the Launch_Thread() function.
+ */
+ Push(kthread, KERNEL_CS);
+ Push(kthread, (ulong_t) &Launch_Thread);
+
+ /* Push fake error code and interrupt number. */
+ Push(kthread, 0);
+ Push(kthread, 0);
+
+ /* Push initial values for general-purpose registers. */
+ Push_General_Registers(kthread);
+
+ /*
+ * Push values for saved segment registers.
+ * Only the ds and es registers will contain valid selectors.
+ * The fs and gs registers are not used by any instruction
+ * generated by gcc.
+ */
+ Push(kthread, KERNEL_DS); /* ds */
+ Push(kthread, KERNEL_DS); /* es */
+ Push(kthread, 0); /* fs */
+ Push(kthread, 0); /* gs */
+}
+
+
+
+/*
+ * This is the body of the idle thread. Its job is to preserve
+ * the invariant that a runnable thread always exists,
+ * i.e., the run queue is never empty.
+ */
+static void Idle(ulong_t arg)
+{
+ while (true)
+ Yield();
+}
+
+/*
+ * The reaper thread. Its job is to de-allocate memory
+ * used by threads which have finished.
+ */
+static void Reaper(ulong_t arg)
+{
+ struct Kernel_Thread *kthread;
+
+ Disable_Interrupts();
+
+ while (true) {
+ /* See if there are any threads needing disposal. */
+ if ((kthread = s_graveyardQueue.head) == 0) {
+ /* Graveyard is empty, so wait for a thread to die. */
+ Wait(&s_reaperWaitQueue);
+ }
+ else {
+ /* Make the graveyard queue empty. */
+ Clear_Thread_Queue(&s_graveyardQueue);
+
+ /*
+ * Now we can re-enable interrupts, since we
+ * have removed all the threads needing disposal.
+ */
+ Enable_Interrupts();
+ Yield(); /* allow other threads to run? */
+
+ /* Dispose of the dead threads. */
+ while (kthread != 0) {
+ struct Kernel_Thread* next = Get_Next_In_Thread_Queue(kthread);
+#if 0
+ Print("Reaper: disposing of thread @ %x, stack @ %x\n",
+ kthread, kthread->stackPage);
+#endif
+ Destroy_Thread(kthread);
+ kthread = next;
+ }
+
+ /*
+ * Disable interrupts again, since we're going to
+ * do another iteration.
+ */
+ Disable_Interrupts();
+ }
+ }
+}
+
+/*
+ * Find the best (highest priority) thread in given
+ * thread queue. Returns null if queue is empty.
+ */
+static __inline__ struct Kernel_Thread* Find_Best(struct Thread_Queue* queue)
+{
+ /* Pick the highest priority thread */
+ struct Kernel_Thread *kthread = queue->head, *best = 0;
+ while (kthread != 0) {
+ if (best == 0 || kthread->priority > best->priority)
+ best = kthread;
+ kthread = Get_Next_In_Thread_Queue(kthread);
+ }
+ return best;
+}
+
+/*
+ * Acquires pointer to thread-local data from the current thread
+ * indexed by the given key. Assumes interrupts are off.
+ */
+static __inline__ const void** Get_Tlocal_Pointer(tlocal_key_t k)
+{
+ struct Kernel_Thread* current = g_currentThread;
+
+ KASSERT(k < MAX_TLOCAL_KEYS);
+
+ return ¤t->tlocalData[k];
+}
+
+/*
+ * Clean up any thread-local data upon thread exit. Assumes
+ * this is called with interrupts disabled. We follow the POSIX style
+ * of possibly invoking a destructor more than once, because a
+ * destructor to some thread-local data might cause other thread-local
+ * data to become alive once again. If everything is NULL by the end
+ * of an iteration, we are done.
+ */
+static void Tlocal_Exit(struct Kernel_Thread* curr) {
+ int i, j, called = 0;
+
+ KASSERT(!Interrupts_Enabled());
+
+ for (j = 0; j<MIN_DESTRUCTOR_ITERATIONS; j++) {
+
+ for (i = 0; i<MAX_TLOCAL_KEYS; i++) {
+
+ void *x = (void *)curr->tlocalData[i];
+ if (x != NULL && s_tlocalDestructors[i] != NULL) {
+
+ curr->tlocalData[i] = NULL;
+ called = 1;
+
+ Enable_Interrupts();
+ s_tlocalDestructors[i](x);
+ Disable_Interrupts();
+ }
+ }
+ if (!called) break;
+ }
+}
+
+
+/* ----------------------------------------------------------------------
+ * Public functions
+ * ---------------------------------------------------------------------- */
+
+void Init_Scheduler(void)
+{
+ struct Kernel_Thread* mainThread = (struct Kernel_Thread *) KERNEL_THREAD_OBJECT;
+
+ PrintBoth("Initializing Scheduler\n");
+
+ /*
+ * Create initial kernel thread context object and stack,
+ * and make them current.
+ */
+ Init_Thread(mainThread, (void *) KERNEL_STACK, PRIORITY_NORMAL, true);
+ g_currentThread = mainThread;
+ Add_To_Back_Of_All_Thread_List(&s_allThreadList, mainThread);
+
+ /*
+ * Create the idle thread.
+ */
+ /*Print("starting idle thread\n");*/
+ Start_Kernel_Thread(Idle, 0, PRIORITY_IDLE, true);
+
+ /*
+ * Create the reaper thread.
+ */
+ /*Print("starting reaper thread\n");*/
+ Start_Kernel_Thread(Reaper, 0, PRIORITY_NORMAL, true);
+}
+
+/*
+ * Start a kernel-mode-only thread, using given function as its body
+ * and passing given argument as its parameter. Returns pointer
+ * to the new thread if successful, null otherwise.
+ *
+ * startFunc - is the function to be called by the new thread
+ * arg - is a paramter to pass to the new function
+ * priority - the priority of this thread (use PRIORITY_NORMAL) for
+ * most things
+ * detached - use false for kernel threads
+ */
+struct Kernel_Thread* Start_Kernel_Thread(
+ Thread_Start_Func startFunc,
+ ulong_t arg,
+ int priority,
+ bool detached
+)
+{
+ struct Kernel_Thread* kthread = Create_Thread(priority, detached);
+ if (kthread != 0) {
+ /*
+ * Create the initial context for the thread to make
+ * it schedulable.
+ */
+ Setup_Kernel_Thread(kthread, startFunc, arg);
+
+
+ /* Atomically put the thread on the run queue. */
+ Make_Runnable_Atomic(kthread);
+ }
+
+ return kthread;
+}
+
+/*
+ * Add given thread to the run queue, so that it
+ * may be scheduled. Must be called with interrupts disabled!
+ */
+void Make_Runnable(struct Kernel_Thread* kthread)
+{
+ KASSERT(!Interrupts_Enabled());
+
+ Enqueue_Thread(&s_runQueue, kthread);
+}
+
+/*
+ * Atomically make a thread runnable.
+ * Assumes interrupts are currently enabled.
+ */
+void Make_Runnable_Atomic(struct Kernel_Thread* kthread)
+{
+ Disable_Interrupts();
+ Make_Runnable(kthread);
+ Enable_Interrupts();
+}
+
+/*
+ * Get the thread that currently has the CPU.
+ */
+struct Kernel_Thread* Get_Current(void)
+{
+ return g_currentThread;
+}
+
+/*
+ * Get the next runnable thread from the run queue.
+ * This is the scheduler.
+ */
+struct Kernel_Thread* Get_Next_Runnable(void)
+{
+ struct Kernel_Thread* best = 0;
+
+ best = Find_Best(&s_runQueue);
+ KASSERT(best != 0);
+ Remove_Thread(&s_runQueue, best);
+
+/*
+ * Print("Scheduling %x\n", best);
+ */
+ return best;
+}
+
+/*
+ * Schedule a thread that is waiting to run.
+ * Must be called with interrupts off!
+ * The current thread should already have been placed
+ * on whatever queue is appropriate (i.e., either the
+ * run queue if it is still runnable, or a wait queue
+ * if it is waiting for an event to occur).
+ */
+void Schedule(void)
+{
+ struct Kernel_Thread* runnable;
+
+ /* Make sure interrupts really are disabled */
+ KASSERT(!Interrupts_Enabled());
+
+ /* Preemption should not be disabled. */
+ KASSERT(!g_preemptionDisabled);
+
+ /* Get next thread to run from the run queue */
+ runnable = Get_Next_Runnable();
+
+ /*
+ * Activate the new thread, saving the context of the current thread.
+ * Eventually, this thread will get re-activated and Switch_To_Thread()
+ * will "return", and then Schedule() will return to wherever
+ * it was called from.
+ */
+
+ //SerialPrint("Switch_To_Thread() in Schedule()\n");
+ Switch_To_Thread(runnable);
+}
+
+/*
+ * Voluntarily give up the CPU to another thread.
+ * Does nothing if no other threads are ready to run.
+ */
+void Yield(void)
+{
+ Disable_Interrupts();
+ Make_Runnable(g_currentThread);
+ Schedule();
+ Enable_Interrupts();
+}
+
+/*
+ * Exit the current thread.
+ * Calling this function initiates a context switch.
+ */
+void Exit(int exitCode)
+{
+ struct Kernel_Thread* current = g_currentThread;
+
+ if (Interrupts_Enabled())
+ Disable_Interrupts();
+
+ /* Thread is dead */
+ current->exitCode = exitCode;
+ current->alive = false;
+
+ /* Clean up any thread-local memory */
+ Tlocal_Exit(g_currentThread);
+
+ /* Notify the thread's owner, if any */
+ Wake_Up(¤t->joinQueue);
+
+ /* Remove the thread's implicit reference to itself. */
+ Detach_Thread(g_currentThread);
+
+ /*
+ * Schedule a new thread.
+ * Since the old thread wasn't placed on any
+ * thread queue, it won't get scheduled again.
+ */
+ Schedule();
+
+ /* Shouldn't get here */
+ KASSERT(false);
+ // the build dies on a warning for a 'noreturn' violation
+ // This ensures that this function never returns
+ while(1);
+}
+
+/*
+ * Wait for given thread to die.
+ * Interrupts must be enabled.
+ * Returns the thread exit code.
+ */
+int Join(struct Kernel_Thread* kthread)
+{
+ int exitCode;
+
+ KASSERT(Interrupts_Enabled());
+
+ /* It is only legal for the owner to join */
+ KASSERT(kthread->owner == g_currentThread);
+
+ Disable_Interrupts();
+
+ /* Wait for it to die */
+ while (kthread->alive) {
+ Wait(&kthread->joinQueue);
+ }
+
+ /* Get thread exit code. */
+ exitCode = kthread->exitCode;
+
+ /* Release our reference to the thread */
+ Detach_Thread(kthread);
+
+ Enable_Interrupts();
+
+ return exitCode;
+}
+
+/*
+ * Look up a thread by its process id.
+ * The caller must be the thread's owner.
+ */
+struct Kernel_Thread* Lookup_Thread(int pid)
+{
+ struct Kernel_Thread *result = 0;
+
+ bool iflag = Begin_Int_Atomic();
+
+ /*
+ * TODO: we could remove the requirement that the caller
+ * needs to be the thread's owner by specifying that another
+ * reference is added to the thread before it is returned.
+ */
+
+ result = Get_Front_Of_All_Thread_List(&s_allThreadList);
+ while (result != 0) {
+ if (result->pid == pid) {
+ if (g_currentThread != result->owner)
+ result = 0;
+ break;
+ }
+ result = Get_Next_In_All_Thread_List(result);
+ }
+
+ End_Int_Atomic(iflag);
+
+ return result;
+}
+
+
+/*
+ * Wait on given wait queue.
+ * Must be called with interrupts disabled!
+ * Note that the function will return with interrupts
+ * disabled. This is desirable, because it allows us to
+ * atomically test a condition that can be affected by an interrupt
+ * and wait for it to be satisfied (if necessary).
+ * See the Wait_For_Key() function in keyboard.c
+ * for an example.
+ */
+void Wait(struct Thread_Queue* waitQueue)
+{
+ struct Kernel_Thread* current = g_currentThread;
+
+ KASSERT(!Interrupts_Enabled());
+
+ /* Add the thread to the wait queue. */
+ Enqueue_Thread(waitQueue, current);
+
+ /* Find another thread to run. */
+ Schedule();
+}
+
+/*
+ * Wake up all threads waiting on given wait queue.
+ * Must be called with interrupts disabled!
+ * See Keyboard_Interrupt_Handler() function in keyboard.c
+ * for an example.
+ */
+void Wake_Up(struct Thread_Queue* waitQueue)
+{
+ struct Kernel_Thread *kthread = waitQueue->head, *next;
+
+ KASSERT(!Interrupts_Enabled());
+
+ /*
+ * Walk throught the list of threads in the wait queue,
+ * transferring each one to the run queue.
+ */
+ while (kthread != 0) {
+ next = Get_Next_In_Thread_Queue(kthread);
+ Make_Runnable(kthread);
+ kthread = next;
+ }
+
+ /* The wait queue is now empty. */
+ Clear_Thread_Queue(waitQueue);
+}
+
+/*
+ * Wake up a single thread waiting on given wait queue
+ * (if there are any threads waiting). Chooses the highest priority thread.
+ * Interrupts must be disabled!
+ */
+void Wake_Up_One(struct Thread_Queue* waitQueue)
+{
+ struct Kernel_Thread* best;
+
+ KASSERT(!Interrupts_Enabled());
+
+ best = Find_Best(waitQueue);
+
+ if (best != 0) {
+ Remove_Thread(waitQueue, best);
+ Make_Runnable(best);
+ /*Print("Wake_Up_One: waking up %x from %x\n", best, g_currentThread); */
+ }
+}
+
+
+
+/*
+ * Wake up a single thread waiting on given wait queue
+ * (if there are any threads waiting). Chooses the highest priority thread.
+ * Interrupts must be disabled!
+ */
+void Wake_Up_Thread(struct Thread_Queue* waitQueue, int pid)
+{
+ struct Kernel_Thread* thread = Lookup_Thread(pid);;
+
+ KASSERT(!Interrupts_Enabled());
+
+
+ if (thread != 0) {
+ Remove_Thread(waitQueue, thread);
+ Make_Runnable(thread);
+ /*Print("Wake_Up_One: waking up %x from %x\n", best, g_currentThread); */
+ }
+}
+
+
+
+
+/*
+ * Allocate a key for accessing thread-local data.
+ */
+int Tlocal_Create(tlocal_key_t *key, tlocal_destructor_t destructor)
+{
+ KASSERT(key);
+
+ bool iflag = Begin_Int_Atomic();
+
+ if (s_tlocalKeyCounter == MAX_TLOCAL_KEYS) return -1;
+ s_tlocalDestructors[s_tlocalKeyCounter] = destructor;
+ *key = s_tlocalKeyCounter++;
+
+ End_Int_Atomic(iflag);
+
+ return 0;
+}
+
+/*
+ * Store a value for a thread-local item
+ */
+void Tlocal_Put(tlocal_key_t k, const void *v)
+{
+ const void **pv;
+
+ KASSERT(k < s_tlocalKeyCounter);
+
+ pv = Get_Tlocal_Pointer(k);
+ *pv = v;
+}
+
+/*
+ * Acquire a thread-local value
+ */
+void *Tlocal_Get(tlocal_key_t k)
+{
+ const void **pv;
+
+ KASSERT(k < s_tlocalKeyCounter);
+
+ pv = Get_Tlocal_Pointer(k);
+ return (void *)*pv;
+}
+
+/*
+ * Print list of all threads in system.
+ * For debugging.
+ */
+void Dump_All_Thread_List(void)
+{
+ struct Kernel_Thread *kthread;
+ int count = 0;
+ bool iflag = Begin_Int_Atomic();
+
+ kthread = Get_Front_Of_All_Thread_List(&s_allThreadList);
+
+ Print("[");
+ while (kthread != 0) {
+ ++count;
+ Print("<%lx,%lx,%lx>",
+ (ulong_t) Get_Prev_In_All_Thread_List(kthread),
+ (ulong_t) kthread,
+ (ulong_t) Get_Next_In_All_Thread_List(kthread));
+ KASSERT(kthread != Get_Next_In_All_Thread_List(kthread));
+ kthread = Get_Next_In_All_Thread_List(kthread);
+ }
+ Print("]\n");
+ Print("%d threads are running\n", count);
+
+ End_Int_Atomic(iflag);
+}
