diff --git a/native/fd.c b/native/fd.c
index 45b7cbd5c6..3e2da54873 100644
--- a/native/fd.c
+++ b/native/fd.c
@@ -14,7 +14,7 @@ int read_step(PORT* port)
 {
 	FIXNUM amount = -1;
 
-	add_read_io_task(port,F);
+	add_io_task(IO_TASK_READ_LINE,port,F);
 
 	for(;;)
 	{
@@ -26,7 +26,7 @@ int read_step(PORT* port)
 		{
 			if(errno != EAGAIN)
 			{
-				remove_read_io_task(port);
+				remove_io_task(IO_TASK_READ_LINE,port);
 				return -1;
 			}
 		}
@@ -36,7 +36,7 @@ int read_step(PORT* port)
 		iomux();
 	}
 
-	remove_read_io_task(port);
+	remove_io_task(IO_TASK_READ_LINE,port);
 
 	port->buf_fill = (amount < 0 ? 0 : amount);
 	port->buf_pos = 0;
@@ -111,39 +111,29 @@ void primitive_read_line_fd_8(void)
 	}
 }
 
-void write_step(PORT* port)
+/* Return true if write was done */
+bool write_step(PORT* port)
 {
 	char* chars = (char*)port->buffer + sizeof(STRING);
 
-	FIXNUM amount;
+	FIXNUM amount = write(port->fd,chars + port->buf_pos,
+		port->buf_fill - port->buf_pos);
 
-	add_write_io_task(port,F);
-
-	for(;;)
+	if(amount == -1)
 	{
-		amount = write(port->fd,chars + port->buf_pos,
-			port->buf_fill - port->buf_pos);
-
-		if(amount == -1)
-		{
-			if(errno != EAGAIN)
-			{
-				remove_write_io_task(port);
-				return;
-			}
-		}
+		if(errno == EAGAIN)
+			return false;
 		else
-			break;
-
-		iomux();
+		{
+			io_error(__FUNCTION__);
+			return false;
+		}
+	}
+	else
+	{
+		port->buf_pos += amount;
+		return true;
 	}
-
-	remove_write_io_task(port);
-
-	if(amount < 0)
-		io_error(__FUNCTION__);
-
-	port->buf_pos += amount;
 }
 
 /* keep writing to the stream until everything is written */
@@ -152,14 +142,19 @@ void flush_buffer(PORT* port)
 	if(port->buf_mode != B_WRITE || port->buf_fill == 0)
 		return;
 
+	add_io_task(IO_TASK_WRITE,port,F);
+
 	for(;;)
 	{
 		if(port->buf_fill == port->buf_pos)
 			break;
 
-		write_step(port);
+		if(!write_step(port))
+			iomux();
 	}
 
+	remove_io_task(IO_TASK_WRITE,port);
+
 	port->buf_pos = 0;
 	port->buf_fill = 0;
 }
diff --git a/native/fd.h b/native/fd.h
index 71f91f3091..a396f0fa5f 100644
--- a/native/fd.h
+++ b/native/fd.h
@@ -7,6 +7,7 @@ int read_step(PORT* port);
 typedef enum { READLINE_AGAIN, READLINE_EOL, READLINE_EOF } READLINE_STAT;
 
 READLINE_STAT read_line_step(PORT* port);
+bool write_step(PORT* port);
 void flush_buffer(PORT* port);
 void init_io(void);
 void primitive_read_line_fd_8(void);
diff --git a/native/gc.c b/native/gc.c
index ea652a4377..5c9a5b5a79 100644
--- a/native/gc.c
+++ b/native/gc.c
@@ -111,7 +111,7 @@ void collect_next(void)
 	}
 }
 
-void copy_roots(void)
+void collect_roots(void)
 {
 	int i;
 
@@ -140,7 +140,8 @@ void primitive_gc(void)
 {
 	flip_zones();
 	scan = active->here = active->base;
-	copy_roots();
+	collect_roots();
+	collect_io_tasks();
 	while(scan < active->here)
 	{
 		gc_debug("scan loop",scan);
diff --git a/native/iomux.c b/native/iomux.c
index 5d42a31ace..4d1a3634d8 100644
--- a/native/iomux.c
+++ b/native/iomux.c
@@ -7,7 +7,7 @@ void init_io_tasks(fd_set* fdset, IO_TASK* io_tasks)
 	FD_ZERO(fdset);
 	for(i = 0; i < FD_SETSIZE; i++)
 	{
-		read_io_tasks[i].port = NULL;
+		read_io_tasks[i].port = F;
 		read_io_tasks[i].callback = F;
 	}
 }
@@ -21,7 +21,8 @@ void init_iomux(void)
 	init_io_tasks(&write_fd_set,write_io_tasks);
 }
 
-void add_io_task(
+void add_io_task_impl(
+	IO_TASK_TYPE type,
 	PORT* port,
 	CELL callback,
 	fd_set* fdset,
@@ -34,10 +35,11 @@ void add_io_task(
 	int i;
 	for(i = 0; i < fds; i++)
 	{
-		if(io_tasks[i].port == NULL)
+		if(io_tasks[i].port == F)
 		{
 			FD_SET(port->fd,fdset);
-			io_tasks[i].port = port;
+			io_tasks[i].type = type;
+			io_tasks[i].port = tag_object(port);
 			io_tasks[i].callback = callback;
 			return;
 		}
@@ -48,26 +50,32 @@ void add_io_task(
 		critical_error("Too many I/O tasks",*fd_count);
 
 	FD_SET(port->fd,fdset);
-	io_tasks[fds].port = port;
+	io_tasks[fds].type = type;
+	io_tasks[fds].port = tag_object(port);
 	io_tasks[fds].callback = callback;
 	*fd_count = fds + 1;
 }
 
-void add_read_io_task(PORT* port, CELL callback)
+void add_io_task(IO_TASK_TYPE type, PORT* port, CELL callback)
 {
-	add_io_task(port,callback,
-		&read_fd_set,read_io_tasks,
-		&read_fd_count);
+	switch(type)
+	{
+	case IO_TASK_READ_LINE:
+	case IO_TASK_READ_COUNT:
+		add_io_task_impl(type,port,callback,
+			&read_fd_set,read_io_tasks,
+			&read_fd_count);
+		break;
+	case IO_TASK_WRITE:
+		add_io_task_impl(type,port,callback,
+			&write_fd_set,write_io_tasks,
+			&write_fd_count);
+		break;
+	}
 }
 
-void add_write_io_task(PORT* port, CELL callback)
-{
-	add_io_task(port,callback,
-		&write_fd_set,write_io_tasks,
-		&write_fd_count);
-}
-
-void remove_io_task(
+void remove_io_task_impl(
+	IO_TASK_TYPE type,
 	PORT* port,
 	fd_set* fdset,
 	IO_TASK* io_tasks,
@@ -78,10 +86,10 @@ void remove_io_task(
 
 	for(i = 0; i < fds; i++)
 	{
-		if(io_tasks[i].port == port)
+		if(untag_port(io_tasks[i].port) == port)
 		{
 			FD_CLR(port->fd,fdset);
-			io_tasks[i].port = NULL;
+			io_tasks[i].port = F;
 			io_tasks[i].callback = F;
 			if(i == fds - 1)
 				*fd_count = fds - 1;
@@ -90,14 +98,40 @@ void remove_io_task(
 	}
 }
 
-void remove_read_io_task(PORT* port)
+void remove_io_task(IO_TASK_TYPE type, PORT* port)
 {
-	remove_io_task(port,&read_fd_set,read_io_tasks,&read_fd_count);
+	switch(type)
+	{
+	case IO_TASK_READ_LINE:
+	case IO_TASK_READ_COUNT:
+		remove_io_task_impl(type,port,
+			&read_fd_set,read_io_tasks,
+			&read_fd_count);
+		break;
+	case IO_TASK_WRITE:
+		remove_io_task_impl(type,port,
+			&write_fd_set,write_io_tasks,
+			&write_fd_count);
+	}
 }
 
-void remove_write_io_task(PORT* port)
+void perform_iotask(IO_TASK* task)
 {
-	remove_io_task(port,&write_fd_set,write_io_tasks,&write_fd_count);
+	if(task->port == F)
+		return;
+
+	switch(task->type)
+	{
+	case IO_TASK_READ_LINE:
+		
+		break;
+	case IO_TASK_WRITE:
+		write_step(untag_port(task->port));
+		break;
+	default:
+		critical_error("Bad I/O task",task->type);
+		break;
+	}
 }
 
 /* Wait for I/O and return a callback. */
@@ -107,5 +141,30 @@ CELL iomux(void)
 		? read_fd_count : write_fd_count,
 		&read_fd_set,&write_fd_set,NULL,NULL);
 
+	/* int i;
+
+	for(i = 0; i < read_fd_count; i++)
+		perform_iotask(&read_io_tasks[i]);
+
+	for(i = 0; i < write_fd_count; i++)
+		perform_iotask(&write_io_tasks[i]); */
+
 	return F;
 }
+
+void collect_io_tasks(void)
+{
+	int i;
+
+	for(i = 0; i < FD_SETSIZE; i++)
+	{
+		copy_object(&read_io_tasks[i].port);
+		copy_object(&read_io_tasks[i].callback);
+	}
+
+	for(i = 0; i < FD_SETSIZE; i++)
+	{
+		copy_object(&write_io_tasks[i].port);
+		copy_object(&write_io_tasks[i].callback);
+	}
+}
diff --git a/native/iomux.h b/native/iomux.h
index 2018dcda76..411eb2b6bf 100644
--- a/native/iomux.h
+++ b/native/iomux.h
@@ -1,5 +1,12 @@
+typedef enum {
+	IO_TASK_READ_LINE,
+	IO_TASK_READ_COUNT,
+	IO_TASK_WRITE
+} IO_TASK_TYPE;
+
 typedef struct {
-	PORT* port;
+	IO_TASK_TYPE type;
+	CELL port;
 	CELL callback;
 } IO_TASK;
 
@@ -13,19 +20,20 @@ int write_fd_count;
 
 void init_io_tasks(fd_set* fd_set, IO_TASK* io_tasks);
 void init_iomux(void);
-void add_io_task(
+void add_io_task_impl(
+	IO_TASK_TYPE type,
 	PORT* port,
 	CELL callback,
-	fd_set* fd_set,
+	fd_set* fdset,
 	IO_TASK* io_tasks,
 	int* fd_count);
-void add_read_io_task(PORT* port, CELL callback);
-void add_write_io_task(PORT* port, CELL callback);
-void remove_io_task(
+void add_io_task(IO_TASK_TYPE type, PORT* port, CELL callback);
+void remove_io_task_impl(
+	IO_TASK_TYPE type,
 	PORT* port,
 	fd_set* fdset,
 	IO_TASK* io_tasks,
 	int* fd_count);
-void remove_read_io_task(PORT* port);
-void remove_write_io_task(PORT* port);
+void remove_io_task(IO_TASK_TYPE type, PORT* port);
 CELL iomux(void);
+void collect_io_tasks(void);