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make the queue fully nogc and optimize it with a freelist (#161)

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make the queue fully nogc and optimize it with a freelist
merged-on-behalf-of: BBasile <BBasile@users.noreply.github.com>
This commit is contained in:
BBasile 2018-06-13 11:20:31 +02:00 committed by The Dlang Bot
parent 7a2018538c
commit 894982e32d
1 changed files with 192 additions and 127 deletions
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171
source/dyaml/queue.d
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@ -7,13 +7,7 @@
module dyaml.queue;
/// Queue collection.
import core.stdc.stdlib;
import core.memory;
import std.container;
import std.traits;
import std.traits : hasMember, hasIndirections;
package:
@ -22,71 +16,128 @@ package:
/// Needed in some D:YAML code that needs a queue-like structure without too much
/// reallocation that goes with an array.
///
/// This should be replaced once Phobos has a decent queue/linked list.
///
/// Uses manual allocation through malloc/free.
///
/// Also has some features uncommon for a queue, e.g. iteration. Couldn't bother with
/// implementing a range, as this is used only as a placeholder until Phobos gets a
/// decent replacement.
/// Allocations are non-GC and are damped by a free-list based on the nodes
/// that are removed. Note that elements lifetime must be managed
/// outside.
struct Queue(T)
if(!hasMember!(T, "__dtor"))
if (!hasMember!(T, "__xdtor"))
{
private:
/// Linked list node containing one element and pointer to the next node.
private:
// Linked list node containing one element and pointer to the next node.
struct Node
{
T payload_;
Node* next_ = null;
Node* next_;
}
/// Start of the linked list - first element added in time (end of the queue).
Node* first_ = null;
/// Last element of the linked list - last element added in time (start of the queue).
Node* last_ = null;
/// Cursor pointing to the current node in iteration.
Node* cursor_ = null;
// Start of the linked list - first element added in time (end of the queue).
Node* first_;
// Last element of the linked list - last element added in time (start of the queue).
Node* last_;
// Cursor pointing to the current node in iteration.
Node* cursor_;
// free-list
Node* stock;
/// Length of the queue.
size_t length_ = 0;
// Length of the queue.
size_t length_;
// allocate a new node or recycle one from the stock.
Node* makeNewNode(T thePayload, Node* theNext = null) @trusted nothrow @nogc
{
import std.experimental.allocator : make;
import std.experimental.allocator.mallocator : Mallocator;
Node* result;
if (stock !is null)
{
result = stock;
stock = result.next_;
result.payload_ = thePayload;
result.next_ = theNext;
}
else
{
result = Mallocator.instance.make!(Node)(thePayload, theNext);
// GC can dispose T managed member if it thinks they are no used...
static if (hasIndirections!T)
{
import core.memory : GC;
GC.addRange(result, Node.sizeof);
}
}
return result;
}
// free the stock of available free nodes.
void freeStock() @trusted @nogc nothrow
{
import std.experimental.allocator.mallocator : Mallocator;
while (stock !is null)
{
Node* toFree = stock;
stock = stock.next_;
static if (hasIndirections!T)
{
import core.memory : GC;
GC.removeRange(toFree);
}
Mallocator.instance.deallocate((cast(ubyte*) toFree)[0 .. Node.sizeof]);
}
}
public:
public:
@disable void opAssign(ref Queue);
@disable bool opEquals(ref Queue);
@disable int opCmp(ref Queue);
@disable this(this);
~this() @safe nothrow @nogc
{
freeStock();
stock = first_;
freeStock();
}
/// Start iterating over the queue.
void startIteration() @safe pure nothrow @nogc
{
cursor_ = first_;
}
/// Get next element in the queue.
/// Returns: The next element in the queue.
ref const(T) next() @safe pure nothrow @nogc
in
{
assert(!empty);
assert(cursor_ !is null);
}
body
do
{
const previous = cursor_;
cursor_ = cursor_.next_;
return previous.payload_;
}
/// Are we done iterating?
/// Returns: true if itrating is not possible anymore, false otherwise.
bool iterationOver() @safe pure nothrow const @nogc
{
return cursor_ is null;
}
/// Push new item to the queue.
void push(T item) @safe nothrow
/// Push a new item to the queue.
void push(T item) @nogc @safe nothrow
{
Node* newLast = new Node(item, null);
if(last_ !is null) { last_.next_ = newLast; }
if(first_ is null) { first_ = newLast; }
Node* newLast = makeNewNode(item);
if (last_ !is null)
last_.next_ = newLast;
if (first_ is null)
first_ = newLast;
last_ = newLast;
++length_;
}
@ -97,40 +148,54 @@ struct Queue(T)
{
assert(idx <= length_);
}
body
do
{
if(idx == 0)
if (idx == 0)
{
first_ = new Node(item, first_);
first_ = makeNewNode(item, first_);
++length_;
}
// Adding before last added element, so we can just push.
else if(idx == length_) { push(item); }
else if (idx == length_)
{
push(item);
}
else
{
// Get the element before one we're inserting.
Node* current = first_;
foreach(i; 1 .. idx) { current = current.next_; }
foreach (i; 1 .. idx)
current = current.next_;
assert(current);
// Insert a new node after current, and put current.next_ behind it.
current.next_ = new Node(item, current.next_);
current.next_ = makeNewNode(item, current.next_);
++length_;
}
}
/// Return the next element in the queue and remove it.
/// Returns: The next element in the queue and remove it.
T pop() @safe nothrow
in
{
assert(!empty, "Trying to pop an element from an empty queue");
}
body
do
{
T result = peek();
Node* popped = first_;
Node* oldStock = stock;
Node* old = first_;
first_ = first_.next_;
if(--length_ == 0)
// start the stock from the popped element
stock = old;
old.next_ = null;
// add the existing "old" stock to the new first stock element
if (oldStock !is null)
stock.next_ = oldStock;
if (--length_ == 0)
{
assert(first_ is null);
last_ = null;
@ -139,35 +204,35 @@ struct Queue(T)
return result;
}
/// Return the next element in the queue.
/// Returns: The next element in the queue.
ref inout(T) peek() @safe pure nothrow inout @nogc
in
{
assert(!empty, "Trying to peek at an element in an empty queue");
}
body
do
{
return first_.payload_;
}
/// Is the queue empty?
/// Returns: true of the queue empty, false otherwise.
bool empty() @safe pure nothrow const @nogc
{
return first_ is null;
}
/// Return number of elements in the queue.
/// Returns: The number of elements in the queue.
size_t length() @safe pure nothrow const @nogc
{
return length_;
}
}
@safe unittest
@safe nothrow unittest
{
auto queue = Queue!int();
assert(queue.empty);
foreach(i; 0 .. 65)
foreach (i; 0 .. 65)
{
queue.push(5);
assert(queue.pop() == 5);
@ -176,7 +241,7 @@ struct Queue(T)
}
int[] array = [1, -1, 2, -2, 3, -3, 4, -4, 5, -5];
foreach(i; array)
foreach (i; array)
{
queue.push(i);
}
@ -187,7 +252,7 @@ struct Queue(T)
queue.insert(42, queue.length);
int[] array2;
while(!queue.empty)
while (!queue.empty)
{
array2 ~= queue.pop();
}