[9c191ee] | 1 | /* |
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| 2 | * SuperCore RWLock Handler -- Release a RWLock |
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| 3 | * |
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| 4 | * COPYRIGHT (c) 1989-2006. |
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| 5 | * On-Line Applications Research Corporation (OAR). |
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| 6 | * |
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| 7 | * The license and distribution terms for this file may be |
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| 8 | * found in the file LICENSE in this distribution or at |
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| 9 | * http://www.rtems.com/license/LICENSE. |
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| 10 | * |
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| 11 | * $Id$ |
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| 12 | */ |
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| 13 | |
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| 14 | #if HAVE_CONFIG_H |
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| 15 | #include "config.h" |
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| 16 | #endif |
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| 17 | |
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| 18 | #include <rtems/system.h> |
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| 19 | #include <rtems/score/corerwlock.h> |
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| 20 | #include <rtems/score/states.h> |
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| 21 | #include <rtems/score/thread.h> |
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| 22 | #include <rtems/score/watchdog.h> |
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| 23 | |
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| 24 | /*PAGE |
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| 25 | * |
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| 26 | * _CORE_RWLock_Release |
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| 27 | * |
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| 28 | * This function releases the rwlock. |
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| 29 | * |
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| 30 | * Input parameters: |
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| 31 | * the_rwlock - the rwlock control block to initialize |
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| 32 | * |
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| 33 | * Output parameters: NONE |
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| 34 | */ |
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| 35 | |
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| 36 | CORE_RWLock_Status _CORE_RWLock_Release( |
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| 37 | CORE_RWLock_Control *the_rwlock |
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| 38 | ) |
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| 39 | { |
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| 40 | ISR_Level level; |
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| 41 | Thread_Control *executing = _Thread_Executing; |
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[6bc7a5e] | 42 | Thread_Control *next; |
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[9c191ee] | 43 | |
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| 44 | /* |
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| 45 | * If unlocked, then OK to read. |
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| 46 | * Otherwise, we have to block. |
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| 47 | * If locked for reading and no waiters, then OK to read. |
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| 48 | * If any thread is waiting, then we wait. |
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| 49 | */ |
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| 50 | |
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| 51 | _ISR_Disable( level ); |
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| 52 | switch ( the_rwlock->current_state ) { |
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| 53 | case CORE_RWLOCK_UNLOCKED: |
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| 54 | _ISR_Enable( level ); |
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| 55 | executing->Wait.return_code = CORE_RWLOCK_UNAVAILABLE; |
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| 56 | return CORE_RWLOCK_SUCCESSFUL; |
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| 57 | |
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| 58 | case CORE_RWLOCK_LOCKED_FOR_READING: |
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| 59 | the_rwlock->number_of_readers -= 1; |
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| 60 | if ( the_rwlock->number_of_readers != 0 ) { |
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| 61 | /* must be unlocked again */ |
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| 62 | _ISR_Enable( level ); |
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| 63 | return CORE_RWLOCK_SUCCESSFUL; |
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| 64 | } |
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| 65 | executing->Wait.return_code = CORE_RWLOCK_SUCCESSFUL; |
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| 66 | break; |
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| 67 | case CORE_RWLOCK_LOCKED_FOR_WRITING: |
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[6bc7a5e] | 68 | executing->Wait.return_code = CORE_RWLOCK_SUCCESSFUL; |
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[9c191ee] | 69 | break; |
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| 70 | } |
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| 71 | |
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| 72 | /* |
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| 73 | * Implicitly transition to "unlocked" and find another thread interested |
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| 74 | * in obtaining this rwlock. |
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| 75 | */ |
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[6bc7a5e] | 76 | the_rwlock->current_state = CORE_RWLOCK_UNLOCKED; |
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| 77 | _ISR_Enable( level ); |
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| 78 | |
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| 79 | next = _Thread_queue_Dequeue( &the_rwlock->Wait_queue ); |
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| 80 | |
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[e5200d5] | 81 | if ( next ) { |
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[1d56a7a] | 82 | if ( next->Wait.option == CORE_RWLOCK_THREAD_WAITING_FOR_WRITE ) { |
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| 83 | the_rwlock->current_state = CORE_RWLOCK_LOCKED_FOR_WRITING; |
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| 84 | return CORE_RWLOCK_SUCCESSFUL; |
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| 85 | } |
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[9c191ee] | 86 | |
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[1d56a7a] | 87 | /* |
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| 88 | * Must be CORE_RWLOCK_THREAD_WAITING_FOR_READING |
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| 89 | */ |
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| 90 | the_rwlock->number_of_readers += 1; |
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| 91 | the_rwlock->current_state = CORE_RWLOCK_LOCKED_FOR_READING; |
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[9c191ee] | 92 | |
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[1d56a7a] | 93 | /* |
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| 94 | * Now see if more readers can be let go. |
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| 95 | */ |
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| 96 | while ( 1 ) { |
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| 97 | next = _Thread_queue_First( &the_rwlock->Wait_queue ); |
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| 98 | if ( !next || |
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| 99 | next->Wait.option == CORE_RWLOCK_THREAD_WAITING_FOR_WRITE ) |
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| 100 | return CORE_RWLOCK_SUCCESSFUL; |
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| 101 | the_rwlock->number_of_readers += 1; |
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| 102 | _Thread_queue_Extract( &the_rwlock->Wait_queue, next ); |
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| 103 | } |
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| 104 | } |
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| 105 | /* indentation is to match _ISR_Disable at top */ |
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[e5200d5] | 106 | |
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[9c191ee] | 107 | return CORE_RWLOCK_SUCCESSFUL; |
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| 108 | } |
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