[kernel] Add channel objects

Add the channel object for sending messages between threads. Currently
no good of passing channels to other threads, but global variables in a
single process work. Currently channels are slow and do double copies,
need to refine more.

Tags: ipc

src/kernel/objects/channel.cpp

@@ -0,0 +1,70 @@
+#include "kutil/assert.h"
+
+#include "objects/channel.h"
+
+channel::channel() :
+	m_len(0),
+	m_capacity(0),
+	m_data(nullptr),
+	kobject(kobject::type::channel, j6_signal_channel_can_send)
+{
+}
+
+channel::~channel()
+{
+	kutil::kfree(m_data);
+}
+
+j6_status_t
+channel::enqueue(size_t len, void *data)
+{
+	// TODO: Make this thread safe!
+	if (closed())
+		return j6_status_closed;
+
+	if (!can_send())
+		return j6_err_not_ready;
+
+	if (m_capacity < len) {
+		kutil::kfree(m_data);
+		m_data = kutil::kalloc(len);
+		m_capacity = len;
+		kassert(m_data, "Failed to allocate memory to copy channel message");
+	}
+
+	m_len = len;
+	kutil::memcpy(m_data, data, len);
+	assert_signal(j6_signal_channel_can_recv);
+
+	return j6_status_ok;
+}
+
+j6_status_t
+channel::dequeue(size_t *len, void *data)
+{
+	// TODO: Make this thread safe!
+	if (closed())
+		return j6_status_closed;
+
+	if (!can_receive())
+		return j6_err_not_ready;
+
+	if (!len)
+		return j6_err_invalid_arg;
+
+	if (*len < m_len)
+		return j6_err_insufficient;
+
+	kutil::memcpy(data, m_data, m_len);
+	*len = m_len;
+	assert_signal(j6_signal_channel_can_send);
+
+	return j6_status_ok;
+}
+
+void
+channel::on_no_handles()
+{
+	kobject::on_no_handles();
+	delete this;
+}

src/kernel/objects/channel.h

@@ -0,0 +1,49 @@
+#pragma once
+/// \file channel.h
+/// Definition of channel objects and related functions
+
+#include "j6/signals.h"
+#include "objects/kobject.h"
+
+/// Channels are bi-directional means of sending messages
+class channel :
+	public kobject
+{
+public:
+	channel();
+	virtual ~channel();
+
+	/// Check if the channel has space for a message to be sent
+	inline bool can_send() const { return check_signal(j6_signal_channel_can_send); }
+
+	/// Check if the channel has a message wiating already
+	inline bool can_receive() const { return check_signal(j6_signal_channel_can_recv); }
+
+	/// Put a message into the channel
+	/// \arg len  Length of data, in bytes
+	/// \arg data Pointer to the message data
+	/// \returns  j6_status_ok on success
+	j6_status_t enqueue(size_t len, void *data);
+
+	/// Get a message from the channel, copied into a provided buffer
+	/// \arg len  On input, the size of the provided buffer. On output,
+	///           the size of the message copied into the buffer.
+	/// \arg data Pointer to the buffer
+	/// \returns  j6_status_ok on success
+	j6_status_t dequeue(size_t *len, void *data);
+
+	/// Mark this channel as closed, all future calls to enqueue or
+	/// dequeue messages will fail with j6_status_closed.
+	inline void close() { assert_signal(j6_signal_channel_closed); }
+
+	/// Check if this channel has been closed
+	inline bool closed() { return check_signal(j6_signal_channel_closed); }
+
+protected:
+	virtual void on_no_handles() override;
+
+private:
+	size_t m_len;
+	size_t m_capacity;
+	void *m_data;
+};

src/kernel/objects/kobject.h

@@ -19,6 +19,7 @@ public:
 
 		event,
 		eventpair,
+		channel,
 
 		vms,
 		vmo,
@@ -55,6 +56,10 @@ public:
 	/// \arg s  The set of signals to deassert
 	void deassert_signal(j6_signal_t s);
 
+	/// Check if the given signals are set on this object
+	/// \arg s  The set of signals to check
+	inline bool check_signal(j6_signal_t s) const { return (m_signals & s) == s; }
+
 	/// Increment the handle refcount
 	inline void handle_retain() { ++m_handle_count; }