kernel: Add event queue implementation to wait for objects efficiently.

Based on hamishm's original patch from 2015, but heavily modified,
refactored, and reworked.

From the original commit message:

> When an object is deleted, a B_EVENT_INVALID event is delivered,
> and the object is unregistered from the queue.
>
> The special event flag B_EVENT_ONE_SHOT can be passed in when adding
> an object so that the object is automatically unregistered when an
> event is delivered.

Modifications to the original change include:

 * Removed the public interface (syscalls remain private for the moment)

 * Event list queueing/dequeueing almost entirely rewritten, including:
  - Clear events field when dequeueing.

  - Have B_EVENT_QUEUED actually indicate whether the event has been
    appended to the linked list (or not), based around lock state.
    The previous logic was prone to races and double-insertions.

  - "Modify" is now just "Deselect + Select" performed at once;
    previously it could cause use-after-frees.

  - Unlock for deselect only once at the end of dequeue.

  - Handle INVALID events still in the queue upon destruction,
    fixing memory leaks.

 * Deduplified code with wait_for_objects.

 * Use of C++ virtual dispatch instead of C-style enum + function calls,
   and BReferenceable plus destructors for teardown.

 * Removed select/modify/delete flags. Select/Modify are now the same
   operation on the syscall interface, and "Delete" is done when 0
   is passed for "events". Additionally, the events selected can be fetched
   by passing -1 for "events".

 * Implemented level-triggered mode.

 * Use of BStackOrHeapArray and other convenience routines in syscalls.

Change-Id: I1d2f094fd981c95215a59adbc087523c7bbbe40b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6745
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: Jérôme Duval <[email protected]>

headers/os/kernel/OS.h

@@ -636,7 +636,7 @@ enum {
 
 	B_EVENT_ACQUIRE_SEMAPHORE	= 0x0001,	/* semaphore can be acquired */
 
-	B_EVENT_INVALID				= 0x1000	/* FD/port/sem/thread ID not or
+	B_EVENT_INVALID				= 0x1000,	/* FD/port/sem/thread ID not or
 											   no longer valid (e.g. has been
 											   close/deleted) */
 };

headers/private/kernel/event_queue.h

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2015, Hamish Morrison, [email protected].
+ * All rights reserved. Distributed under the terms of the MIT License.
+ */
+
+#ifndef _KERNEL_EVENT_QUEUE_H
+#define _KERNEL_EVENT_QUEUE_H
+
+#include <OS.h>
+#include <event_queue_defs.h>
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+extern int		_user_event_queue_create(int openFlags);
+extern status_t	_user_event_queue_select(int queue,	event_wait_info* userInfos,
+					int numInfos);
+extern ssize_t	_user_event_queue_wait(int queue, event_wait_info* infos,
+					int numInfos, uint32 flags, bigtime_t timeout);
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

headers/private/kernel/fs/fd.h

@@ -15,6 +15,7 @@
 extern "C" {
 #endif
 
+struct event_queue;
 struct file_descriptor;
 struct io_context;
 struct net_socket;
@@ -54,6 +55,7 @@ struct file_descriptor {
 		struct vnode *vnode;
 		struct fs_mount *mount;
 		struct net_socket *socket;
+		struct event_queue *queue;
 	} u;
 	void	*cookie;
 	int32	open_mode;
@@ -71,7 +73,8 @@ enum fd_types {
 	FDTYPE_INDEX,
 	FDTYPE_INDEX_DIR,
 	FDTYPE_QUERY,
-	FDTYPE_SOCKET
+	FDTYPE_SOCKET,
+	FDTYPE_EVENT_QUEUE
 };
 
 // additional open mode - kernel special

headers/private/kernel/wait_for_objects.h

@@ -15,18 +15,12 @@ struct select_sync;
 
 
 typedef struct select_info {
-	struct select_info*	next;				// next in the object's list
-	struct select_sync*	sync;
-	int32				events;
-	uint16				selected_events;
+	struct select_info*			next;
+	struct select_sync*			sync;
+	int32						events;
+	uint16						selected_events;
 } select_info;
 
-typedef struct select_sync {
-	int32				ref_count;
-	sem_id				sem;
-	uint32				count;
-	struct select_info*	set;
-} select_sync;
 
 #define SELECT_FLAG(type) (1L << (type - 1))
 
@@ -39,9 +33,10 @@ typedef struct select_sync {
 
 #ifdef __cplusplus
 extern "C" {
-#endif 
+#endif
 
 
+extern void		acquire_select_sync(select_sync* sync);
 extern void		put_select_sync(select_sync* sync);
 extern status_t	notify_select_events(select_info* info, uint16 events);
 extern void		notify_select_events_list(select_info* list, uint16 events);

headers/private/system/event_queue_defs.h

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2023, Haiku, Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _SYSTEM_EVENT_QUEUE_DEFS_H
+#define _SYSTEM_EVENT_QUEUE_DEFS_H
+
+
+// extends B_EVENT_* constants defined in OS.h
+enum {
+	B_EVENT_LEVEL_TRIGGERED		= (1 << 26),	/* Event is level-triggered, not edge-triggered */
+	B_EVENT_ONE_SHOT			= (1 << 27),	/* Delete event after delivery */
+
+	/* bits 28 through 30 are reserved for the kernel */
+};
+
+
+typedef struct event_wait_info {
+	int32		object;
+	uint16		type;
+	int32		events;		/* select(): > 0 to select, -1 to get selection, 0 to deselect */
+	void*		user_data;
+} event_wait_info;
+
+
+#endif	/* _SYSTEM_EVENT_QUEUE_DEFS_H */

headers/private/system/syscalls.h

@@ -23,6 +23,7 @@ extern "C" {
 
 struct attr_info;
 struct dirent;
+struct event_wait_info;
 struct fd_info;
 struct fd_set;
 struct fs_info;
@@ -74,6 +75,12 @@ extern status_t		_kern_get_safemode_option(const char *parameter,
 extern ssize_t		_kern_wait_for_objects(object_wait_info* infos, int numInfos,
 						uint32 flags, bigtime_t timeout);
 
+extern int			_kern_event_queue_create(int openFlags);
+extern status_t		_kern_event_queue_select(int queue,
+						struct event_wait_info* userInfos, int numInfos);
+extern ssize_t		_kern_event_queue_wait(int queue, struct event_wait_info* infos,
+						int numInfos, uint32 flags, bigtime_t timeout);
+
 /* user mutex functions */
 extern status_t		_kern_mutex_lock(int32* mutex, const char* name,
 						uint32 flags, bigtime_t timeout);