WebSVN – HelenOS – Diff – /trunk/kernel/generic/src/ipc/ipcrsc.c



/** @file
 */
 
/* IPC resources management
 *
 * The goal of this source code is to properly manage IPC resources and allow
 * straight and clean clean-up procedure upon task termination.
 *
 * The pattern of usage of the resources is:
 * - allocate empty phone slot, connect | deallocate slot
 * - disconnect connected phone (some messages might be on the fly)
 * - find phone in slot and send a message using phone

 * - hangup phone (the caller has hung up)
 * - hangup phone (the answerbox is exiting)
 *
 * Locking strategy
 *
 * - To use a phone, disconnect a phone etc., the phone must be first locked and
 *   then checked that it is connected
 * - To connect an allocated phone it need not be locked (assigning pointer is
 *   atomic on all platforms)
 *
 * - To find an empty phone slot, the TASK must be locked
 * - To answer a message, the answerbox must be locked
 * - The locking of phone and answerbox is done at the ipc_ level.
 *   It is perfectly correct to pass unconnected phone to these functions and
 *   proper reply will be generated.
 *
 * Locking order
 *
 * - first phone, then answerbox
 *   + Easy locking on calls
 *   - Very hard traversing list of phones when disconnecting because the phones
 *     may disconnect during traversal of list of connected phones. The only
 *     possibility is try_lock with restart of list traversal.
 *
 * Destroying is less frequent, this approach is taken.
 *
 * Phone call
 *
 * *** Connect_me_to ***
 * The caller sends IPC_M_CONNECT_ME_TO to an answerbox. The server receives
 * 'phoneid' of the connecting phone as an ARG3. If it answers with RETVAL=0,
 * the phonecall is accepted, otherwise it is refused.
 *
 * *** Connect_to_me ***
 * The caller sends IPC_M_CONNECT_TO_ME.
 * The server receives an automatically opened phoneid. If it accepts
 * (RETVAL=0), it can use the phoneid immediately.
 
 * Possible race condition can arise, when the client receives messages from new
 * connection before getting response for connect_to_me message. Userspace
 * should implement handshake protocol that would control it.
 *
 * Phone hangup
 *
 * *** The caller hangs up (sys_ipc_hangup) ***
 * - The phone is disconnected (no more messages can be sent over this phone),
 *   all in-progress messages are correctly handled. The answerbox receives
 *   IPC_M_PHONE_HUNGUP call from the phone that hung up. When all async
 *   calls are answered, the phone is deallocated.
 *
 * *** The answerbox hangs up (ipc_answer(EHANGUP))
 * - The phone is disconnected. EHANGUP response code is sent

Subversion Repositories HelenOS

(root)/trunk/kernel/generic/src/ipc/ipcrsc.c @ 2471 – Rev 2071 → 2359

Rev 2071		Rev 2359
Line 32...		Line 32...
32	/** @file	32	/** @file
33	*/	33	*/
34		34
35	/* IPC resources management	35	/* IPC resources management
36	*	36	*
37	* The goal of this source code is to properly manage IPC resources	37	* The goal of this source code is to properly manage IPC resources and allow
38	* and allow straight and clean clean-up procedure upon task termination.	38	* straight and clean clean-up procedure upon task termination.
39	*	39	*
40	* The pattern of usage of the resources is:	40	* The pattern of usage of the resources is:
41	* - allocate empty phone slot, connect \| deallocate slot	41	* - allocate empty phone slot, connect \| deallocate slot
42	* - disconnect connected phone (some messages might be on the fly)	42	* - disconnect connected phone (some messages might be on the fly)
43	* - find phone in slot and send a message using phone	43	* - find phone in slot and send a message using phone
Line 45...		Line 45...
45	* - hangup phone (the caller has hung up)	45	* - hangup phone (the caller has hung up)
46	* - hangup phone (the answerbox is exiting)	46	* - hangup phone (the answerbox is exiting)
47	*	47	*
48	* Locking strategy	48	* Locking strategy
49	*	49	*
50	* - To use a phone, disconnect a phone etc., the phone must be	50	* - To use a phone, disconnect a phone etc., the phone must be first locked and
51	* first locked and then checked that it is connected	51	* then checked that it is connected
52	* - To connect an allocated phone it need not be locked (assigning	52	* - To connect an allocated phone it need not be locked (assigning pointer is
53	* pointer is atomic on all platforms)	53	* atomic on all platforms)
54	*	54	*
55	* - To find an empty phone slot, the TASK must be locked	55	* - To find an empty phone slot, the TASK must be locked
56	* - To answer a message, the answerbox must be locked	56	* - To answer a message, the answerbox must be locked
57	* - The locking of phone and answerbox is done at the ipc_ level.	57	* - The locking of phone and answerbox is done at the ipc_ level.
58	* It is perfectly correct to pass unconnected phone to these functions	58	* It is perfectly correct to pass unconnected phone to these functions and
59	* and proper reply will be generated.	59	* proper reply will be generated.
60	*	60	*
61	* Locking order	61	* Locking order
62	*	62	*
63	* - first phone, then answerbox	63	* - first phone, then answerbox
64	* + Easy locking on calls	64	* + Easy locking on calls
65	* - Very hard traversing list of phones when disconnecting because	65	* - Very hard traversing list of phones when disconnecting because the phones
66	* the phones may disconnect during traversal of list of connected phones.	66	* may disconnect during traversal of list of connected phones. The only
67	* The only possibility is try_lock with restart of list traversal.	67	* possibility is try_lock with restart of list traversal.
68	*	68	*
69	* Destroying is less frequent, this approach is taken.	69	* Destroying is less frequent, this approach is taken.
70	*	70	*
71	* Phone call	71	* Phone call
72	*	72	*
73	* * Connect_me_to *	73	* * Connect_me_to *
74	* The caller sends IPC_M_CONNECT_ME_TO to an answerbox. The server	74	* The caller sends IPC_M_CONNECT_ME_TO to an answerbox. The server receives
75	* receives 'phoneid' of the connecting phone as an ARG3. If it answers	75	* 'phoneid' of the connecting phone as an ARG3. If it answers with RETVAL=0,
76	* with RETVAL=0, the phonecall is accepted, otherwise it is refused.	76	* the phonecall is accepted, otherwise it is refused.
77	*	77	*
78	* * Connect_to_me *	78	* * Connect_to_me *
79	* The caller sends IPC_M_CONNECT_TO_ME, with special	79	* The caller sends IPC_M_CONNECT_TO_ME.
80	* The server receives an automatically	80	* The server receives an automatically opened phoneid. If it accepts
81	* opened phoneid. If it accepts (RETVAL=0), it can use the phoneid	81	* (RETVAL=0), it can use the phoneid immediately.
82	* immediately.	-
83	* Possible race condition can arise, when the client receives messages	82	* Possible race condition can arise, when the client receives messages from new
84	* from new connection before getting response for connect_to_me message.	83	* connection before getting response for connect_to_me message. Userspace
85	* Userspace should implement handshake protocol that would control it.	84	* should implement handshake protocol that would control it.
86	*	85	*
87	* Phone hangup	86	* Phone hangup
88	*	87	*
89	* * The caller hangs up (sys_ipc_hangup) *	88	* * The caller hangs up (sys_ipc_hangup) *
90	* - The phone is disconnected (no more messages can be sent over this phone),	89	* - The phone is disconnected (no more messages can be sent over this phone),
91	* all in-progress messages are correctly handled. The anwerbox receives	90	* all in-progress messages are correctly handled. The answerbox receives
92	* IPC_M_PHONE_HUNGUP call from the phone that hung up. When all async	91	* IPC_M_PHONE_HUNGUP call from the phone that hung up. When all async
93	* calls are answered, the phone is deallocated.	92	* calls are answered, the phone is deallocated.
94	*	93	*
95	* *** The answerbox hangs up (ipc_answer(EHANGUP))	94	* *** The answerbox hangs up (ipc_answer(EHANGUP))
96	* - The phone is disconnected. EHANGUP response code is sent	95	* - The phone is disconnected. EHANGUP response code is sent