Subversion Repositories HelenOS

Rev

Rev 2071 | Rev 2637 | Go to most recent revision | Show entire file | Ignore whitespace | Details | Blame | Last modification | View Log | RSS feed

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