318 lines
10 KiB
C#
318 lines
10 KiB
C#
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//////////////////////////////////////////////////////////////////////////////
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//
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// Microsoft Research Singularity
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//
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// Copyright (c) Microsoft Corporation. All rights reserved.
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//
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// File: HandleTable.cs - Shared region for process handles
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//
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using System;
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using System.Runtime.CompilerServices;
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using System.Runtime.InteropServices;
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using System.Threading;
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using System.GCs;
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using Microsoft.Bartok.Runtime;
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using Microsoft.Singularity;
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namespace Microsoft.Singularity.Memory
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{
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// <summary>
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// Reference-counted handles to object references that aren't garbage
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// collected so they can be handed out across GC domains. The receiving
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// process is handle an actual pointer into the handle table. We know
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// that the process can't forge a non-null pointer due to type safety.
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// Handle table pages for a process are not freed until the process
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// terminates because we hand out pointer within the page to the process.
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//
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// Each page of handles (and therefore each handle) is owned by one process.
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// The pages for a process may be quickly found and deleted upon
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// process death. "Normal" handles never move between processes.
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// Handles related to endpoints can move between processes, but
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// they are owned by the kernel and cleaned up with reference counting
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// since we know that points to handles in channels can never leak.
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//
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// </summary>
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[NoCCtor]
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[CLSCompliant(false)]
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internal class HandleTable {
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internal struct HandlePage
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{
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private UIntPtr table;
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internal unsafe HandlePage * next;
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[Inline]
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internal void SetTable(HandleTable ht)
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{
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table = Magic.addressOf(ht);
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}
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[Inline]
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internal HandleTable GetTable()
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{
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return (HandleTable)Magic.fromAddress(table);
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}
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}
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internal struct HandleEntry {
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internal UIntPtr item;
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internal unsafe HandleEntry * next; // next free node, null if last or in use.
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[Inline]
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internal void Set(Object o)
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{
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item = Magic.addressOf(o);
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}
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[Inline]
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internal Object Get()
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{
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return Magic.fromAddress(item);
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}
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[Inline]
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internal unsafe void Visit(NonNullReferenceVisitor visitor)
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{
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if (item != UIntPtr.Zero) {
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fixed (UIntPtr *loc = &item) {
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visitor.Visit(loc);
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}
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}
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}
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}
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// Per-class members
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private static int handlesPerPage;
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internal static unsafe void Initialize()
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{
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handlesPerPage = (int)((MemoryManager.PageSize / sizeof(HandleEntry)) - 1);
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}
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internal static void Finalize()
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{
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}
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internal static unsafe HandleTable FindOwner(HandleEntry *entry)
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{
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HandlePage * page = (HandlePage *)MemoryManager.PageAlign((UIntPtr)entry);
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return page->GetTable();
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}
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[Inline]
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internal static unsafe void SetHandle(UIntPtr handle, Object obj)
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{
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HandleEntry *entry = (HandleEntry *)handle;
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entry->Set(obj);
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}
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[Inline]
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internal static unsafe void ClrHandle(UIntPtr handle)
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{
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HandleEntry *entry = (HandleEntry *)handle;
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entry->Set(null);
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}
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[Inline]
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internal static unsafe Object GetHandle(UIntPtr handle)
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{
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HandleEntry *entry = (HandleEntry *)handle;
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return entry->Get();
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}
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// Per-instance members
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private Process process;
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private unsafe HandlePage * pages;
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private unsafe HandleEntry * freeList;
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private int pageCount;
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internal unsafe HandleTable(Process process)
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{
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pages = null;
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freeList = null;
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}
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internal unsafe void VisitSpecialData(NonNullReferenceVisitor visitor)
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{
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HandlePage *limit = null;
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HandlePage *began;
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do {
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// Repeat this loop as long as new pages appear.
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// I'm not sure this is needed, the write barrier might
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// take care of this for us.
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began = pages;
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for (HandlePage *page = began; page != limit; page = page->next) {
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// Get the bounds.
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HandleEntry *entry = ((HandleEntry *)(page + 1));
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HandleEntry *elimit = entry + handlesPerPage;
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for (; entry < elimit; entry++) {
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entry->Visit(visitor);
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}
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}
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limit = pages;
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} while (pages != began);
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}
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internal unsafe UIntPtr FreeAllPages()
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{
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// We assume that external code has insured thread safety.
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freeList = null;
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for (HandlePage *next; pages != null; pages = next) {
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next = pages->next;
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MemoryManager.KernelFree((UIntPtr)pages, 1, process);
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}
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return (UIntPtr)pageCount * MemoryManager.PageSize;
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}
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internal unsafe void FreeHandle(UIntPtr handle)
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{
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if (handle != UIntPtr.Zero) {
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FreeEntry((HandleEntry *)handle);
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}
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}
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internal unsafe void FreeEntry(HandleEntry *entry)
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{
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entry->Set(null);
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HandleEntry *next;
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do {
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next = freeList;
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entry->next = next;
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// Interlocked.CompareExchange only updates freeList if it hasn't
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// changed within this loop.
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} while (next != Interlocked.CompareExchange(ref freeList, entry, next));
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}
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internal unsafe UIntPtr AllocateHandle()
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{
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return (UIntPtr)AllocateEntry();
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}
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internal unsafe HandleEntry * AllocateEntry()
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{
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HandleEntry * entry = AllocateExisting();
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if (entry != null) {
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return entry;
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}
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#if SINGULARITY_KERNEL
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Kernel.Waypoint(830);
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#endif // SINGULARITY_KERNEL
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// Need to allocate a new page.
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HandlePage *page
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= (HandlePage*)MemoryManager.KernelAllocate(
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1, process, 0, PageType.Shared);
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#if SINGULARITY_KERNEL
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Kernel.Waypoint(831);
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#endif // SINGULARITY_KERNEL
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if (page == null) {
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return null;
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}
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// Get the bounds.
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HandleEntry *beg = ((HandleEntry *)(page + 1));
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HandleEntry *end = beg + handlesPerPage - 1;
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// Save off the first entry to return.
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entry = beg++;
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entry->Set(null);
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entry->next = null;
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// Initialize the free list in the rest of the entries.
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for (HandleEntry *step = beg; step < end; step++) {
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step->Set(null);
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step->next = step + 1;
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}
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end->Set(null);
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end->next = null;
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// Initialize the page header and insert into the page list.
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page->SetTable(this);
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page->next = null;
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HandlePage *last;
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do {
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last = pages;
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page->next = last;
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// Interlocked.CompareExchange only updates pages if it hasn't
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// changed within this loop.
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} while (last != Interlocked.CompareExchange(ref pages, page, last));
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// Then insert into the free list.
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HandleEntry *next;
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do {
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next = freeList;
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end->next = next;
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// Interlocked.CompareExchange only updates freeList if it hasn't
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// changed with this loop.
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} while (next != Interlocked.CompareExchange(ref freeList, beg, next));
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Interlocked.Increment(ref pageCount);
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return entry;
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}
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internal unsafe HandleEntry * AllocateExisting()
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{
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HandleEntry * first;
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HandleEntry * second;
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do {
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//
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// Cache the contents of head pointer location (i.e. the
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// address of the first element on the list).
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//
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first = freeList;
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if (first == null) {
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//
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// No first element. List is empty.
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//
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return null;
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}
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//
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// The first element contains the address of the second.
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//
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second = first->next;
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//
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// Called this way, Interlocked.CompareExchange will only
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// replace the contents of the head pointer location with
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// the address of the second element if the contents of the
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// the head pointer location (i.e. the first element's address)
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// hasn't changed since we cached it. If the contents of
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// the head pointer have changed in the meantime, it means
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// some other thread has popped that element off the stack.
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// So we loop back and try it all over again.
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//
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} while (first != Interlocked.CompareExchange(ref freeList, second, first));
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first->Set(null);
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first->next = null;
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return first;
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}
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[NoHeapAllocation]
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internal int GetPageCount()
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{
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return pageCount;
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}
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}
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}
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