Merge pull request #25 from vibe-d/channels

Implement typed cross-task channels
merged-on-behalf-of: Leonid Kramer <l-kramer@users.noreply.github.com>

source/vibe/core/channel.d

@@ -0,0 +1,236 @@
+/** Implements a thread-safe, typed producer-consumer queue.
+
+	Copyright: © 2017-2019 RejectedSoftware e.K.
+	Authors: Sönke Ludwig
+	License: Subject to the terms of the MIT license, as written in the included LICENSE.txt file.
+*/
+module vibe.core.channel;
+
+import vibe.core.sync : TaskCondition;
+import vibe.internal.array : FixedRingBuffer;
+
+import std.algorithm.mutation : move, swap;
+import std.exception : enforce;
+import core.sync.mutex;
+
+// multiple producers allowed, multiple consumers allowed - Q: should this be restricted to allow higher performance? maybe configurable?
+// currently always buffered - TODO: implement blocking non-buffered mode
+// TODO: implement a multi-channel wait, e.g.
+// TaggedAlgebraic!(...) consumeAny(ch1, ch2, ch3); - requires a waitOnMultipleConditions function
+
+
+/** Creates a new channel suitable for cross-task and cross-thread communication.
+*/
+Channel!(T, buffer_size) createChannel(T, size_t buffer_size = 100)()
+{
+	Channel!(T, buffer_size) ret;
+	ret.m_impl = new shared ChannelImpl!(T, buffer_size);
+	return ret;
+}
+
+
+/** Thread-safe typed data channel implementation.
+
+	The implementation supports multiple-reader-multiple-writer operation across
+	multiple tasks in multiple threads.
+*/
+struct Channel(T, size_t buffer_size) {
+	enum bufferSize = buffer_size;
+
+	private shared ChannelImpl!(T, buffer_size) m_impl;
+
+	/** Determines whether there is more data to read.
+
+		This property is empty $(I iff) no more elements are in the internal
+		buffer and `close()` has been called. Once the channel is empty,
+		subsequent calls to `consumeOne` or `consumeAll` will throw an
+		exception.
+
+		Note that relying on the return value to determine whether another
+		element can be read is only safe in a single-reader scenario. Use
+		`tryConsumeOne` in a multiple-reader scenario instead.
+	*/
+	@property bool empty() { return m_impl.empty; }
+
+	/** Closes the channel.
+
+		A closed channel does not accept any new items enqueued using `put` and
+		causes `empty` to return `fals` as soon as all preceeding elements have
+		been consumed.
+	*/
+	void close() { m_impl.close(); }
+
+	/** Consumes a single element off the queue.
+
+		This function will block if no elements are available. If the `empty`
+		property is `true`, an exception will be thrown.
+	*/
+	T consumeOne() { return m_impl.consumeOne(); }
+
+	/** Attempts to consume a single element.
+
+		If no more elements are available and the channel has been closed,
+		`false` is returned and `dst` is left untouched.
+	*/
+	bool tryConsumeOne(ref T dst) { return m_impl.tryConsumeOne(dst); }
+
+	/** Attempts to consume all elements currently in the queue.
+
+		This function will block if no elements are available. Once at least one
+		element is available, the contents of `dst` will be replaced with all
+		available elements.
+
+		If the `empty` property is or becomes `true` before data becomes
+		avaiable, `dst` will be left untouched and `false` is returned.
+	*/
+	bool consumeAll(ref FixedRingBuffer!(T, buffer_size) dst)
+	{ return m_impl.consumeAll(dst); }
+
+	/** Enqueues an element.
+
+		This function may block the the event that the internal buffer is full.
+	*/
+	void put(T item) { m_impl.put(item.move); }
+}
+
+
+private final class ChannelImpl(T, size_t buffer_size) {
+	import vibe.core.concurrency : isWeaklyIsolated;
+	static assert(isWeaklyIsolated!T, "Channel data type "~T.stringof~" is not safe to pass between threads.");
+
+	private {
+		Mutex m_mutex;
+		TaskCondition m_condition;
+		FixedRingBuffer!(T, buffer_size) m_items;
+		bool m_closed = false;
+	}
+
+	this()
+	shared {
+		m_mutex = cast(shared)new Mutex;
+		m_condition = cast(shared)new TaskCondition(cast(Mutex)m_mutex);
+	}
+
+	@property bool empty()
+	shared {
+		synchronized (m_mutex) {
+			auto thisus = () @trusted { return cast(ChannelImpl)this; } ();
+			return thisus.m_closed && thisus.m_items.empty;
+		}
+	}
+
+	void close()
+	shared {
+		synchronized (m_mutex) {
+			auto thisus = () @trusted { return cast(ChannelImpl)this; } ();
+			thisus.m_closed = true;
+			thisus.m_condition.notifyAll();
+		}
+	}
+
+	bool tryConsumeOne(ref T dst)
+	shared {
+		auto thisus = () @trusted { return cast(ChannelImpl)this; } ();
+		bool was_full = false;
+
+		synchronized (m_mutex) {
+			while (thisus.m_items.empty) {
+				if (m_closed) return false;
+				thisus.m_condition.wait();
+			}
+			was_full = thisus.m_items.full;
+			move(thisus.m_items.front, dst);
+			thisus.m_items.popFront();
+		}
+
+		if (was_full) thisus.m_condition.notifyAll();
+
+		return true;
+	}
+
+	T consumeOne()
+	shared {
+		auto thisus = () @trusted { return cast(ChannelImpl)this; } ();
+		T ret;
+		bool was_full = false;
+
+		synchronized (m_mutex) {
+			while (thisus.m_items.empty) {
+				if (m_closed) throw new Exception("Attempt to consume from an empty channel.");
+				thisus.m_condition.wait();
+			}
+			was_full = thisus.m_items.full;
+			move(thisus.m_items.front, ret);
+			thisus.m_items.popFront();
+		}
+
+		if (was_full) thisus.m_condition.notifyAll();
+
+		return ret.move;
+	}
+
+	bool consumeAll(ref FixedRingBuffer!(T, buffer_size) dst)
+	shared {
+		auto thisus = () @trusted { return cast(ChannelImpl)this; } ();
+		bool was_full = false;
+
+		synchronized (m_mutex) {
+			while (thisus.m_items.empty) {
+				if (m_closed) return false;
+				thisus.m_condition.wait();
+			}
+
+			was_full = thisus.m_items.full;
+			swap(thisus.m_items, dst);
+		}
+
+		if (was_full) thisus.m_condition.notifyAll();
+
+		return true;
+	}
+
+	void put(T item)
+	shared {
+		auto thisus = () @trusted { return cast(ChannelImpl)this; } ();
+		bool need_notify = false;
+
+		synchronized (m_mutex) {
+			enforce(!m_closed, "Sending on closed channel.");
+			while (thisus.m_items.full)
+				thisus.m_condition.wait();
+			need_notify = thisus.m_items.empty;
+			thisus.m_items.put(item.move);
+		}
+
+		if (need_notify) thisus.m_condition.notifyAll();
+	}
+}
+
+unittest { // test basic operation and non-copyable struct compatiblity
+	static struct S {
+		int i;
+		@disable this(this);
+	}
+
+	auto ch = createChannel!S;
+	ch.put(S(1));
+	assert(ch.consumeOne().i == 1);
+	ch.put(S(4));
+	ch.put(S(5));
+	{
+		FixedRingBuffer!(S, 100) buf;
+		ch.consumeAll(buf);
+		assert(buf.length == 2);
+		assert(buf[0].i == 4);
+		assert(buf[1].i == 5);
+	}
+	ch.put(S(2));
+	assert(!ch.empty);
+	ch.close();
+	assert(!ch.empty);
+	S v;
+	assert(ch.tryConsumeOne(v));
+	assert(v.i == 2);
+	assert(ch.empty);
+	assert(!ch.tryConsumeOne(v));
+}

source/vibe/internal/array.d

@@ -361,7 +361,7 @@ struct FixedRingBuffer(T, size_t N = 0, bool INITIALIZE = true) {
 		m_start = 0;
 	}
 
-	void put()(T itm) { assert(m_fill < m_buffer.length); m_buffer[mod(m_start + m_fill++)] = itm; }
+	void put()(T itm) { assert(m_fill < m_buffer.length); move(itm, m_buffer[mod(m_start + m_fill++)]); }
 	void put(TC : T)(scope TC[] itms)
 	{
 		if( !itms.length ) return;
@@ -391,18 +391,18 @@ struct FixedRingBuffer(T, size_t N = 0, bool INITIALIZE = true) {
 			assert(r.m_start >= m_start && r.m_start < m_buffer.length || r.m_start < mod(m_start+m_fill));
 			if( r.m_start > m_start ){
 				foreach(i; r.m_start .. m_buffer.length-1)
-					m_buffer[i] = m_buffer[i+1];
-				m_buffer[$-1] = m_buffer[0];
+					move(m_buffer[i+1], m_buffer[i]);
+				move(m_buffer[0], m_buffer[$-1]);
 				foreach(i; 0 .. mod(m_start + m_fill - 1))
-					m_buffer[i] = m_buffer[i+1];
+					move(m_buffer[i+1], m_buffer[i]);
 			} else {
 				foreach(i; r.m_start .. mod(m_start + m_fill - 1))
-					m_buffer[i] = m_buffer[i+1];
+					move(m_buffer[i+1], m_buffer[i]);
 			}
 		} else {
 			assert(r.m_start >= m_start && r.m_start < m_start+m_fill);
 			foreach(i; r.m_start .. m_start+m_fill-1)
-				m_buffer[i] = m_buffer[i+1];
+				move(m_buffer[i+1], m_buffer[i]);
 		}
 		m_fill--;
 		destroy(m_buffer[mod(m_start+m_fill)]); // TODO: only call destroy for non-POD T
@@ -422,10 +422,20 @@ struct FixedRingBuffer(T, size_t N = 0, bool INITIALIZE = true) {
 		if( mod(m_start) >= mod(m_start+dst.length) ){
 			size_t chunk1 = m_buffer.length - m_start;
 			size_t chunk2 = dst.length - chunk1;
-			dst[0 .. chunk1] = m_buffer[m_start .. $];
-			dst[chunk1 .. $] = m_buffer[0 .. chunk2];
+			static if (isCopyable!T) {
+				dst[0 .. chunk1] = m_buffer[m_start .. $];
+				dst[chunk1 .. $] = m_buffer[0 .. chunk2];
+			} else {
+				foreach (i; 0 .. chunk1) move(m_buffer[m_start+i], dst[i]);
+				foreach (i; chunk1 .. this.length) move(m_buffer[i-chunk1], dst[i]);
+			}
 		} else {
-			dst[] = m_buffer[m_start .. m_start+dst.length];
+			static if (isCopyable!T) {
+				dst[] = m_buffer[m_start .. m_start+dst.length];
+			} else {
+				foreach (i; 0 .. dst.length)
+					move(m_buffer[m_start + i], dst[i]);
+			}
 		}
 		popFrontN(dst.length);
 	}
@@ -507,7 +517,7 @@ struct FixedRingBuffer(T, size_t N = 0, bool INITIALIZE = true) {
 
 		@property bool empty() const { return m_length == 0; }
 
-		@property inout(T) front() inout { assert(!empty); return m_buffer[m_start]; }
+		@property ref inout(T) front() inout { assert(!empty); return m_buffer[m_start]; }
 
 		void popFront()
 		{