KernelLand/Kernel/rwlock.c

   1 /*
   2  * Acess2 Kernel
   3  * - By John Hodge (thePowersGang)
   4  *
   5  * rwlock.c
   6  * - Reader-Writer Lockes
   7  */
   8 #define DEBUG   0
   9 #include <acess.h>
  10 #include <threads_int.h>
  11 #include <rwlock.h>
  12
  13 // === PROTOTYPES ===
  14 //
  15 // Acquire as a reader (see rwlock.h for documentation)
  16 //
  17 int RWLock_AcquireRead(tRWLock *Lock)
  18 {
  19         LOG("Acquire RWLock Read %p", Lock);
  20         // Get protector
  21         SHORTLOCK( &Lock->Protector );
  22
  23         // Check if the lock is already held by a writer
  24         if( Lock->Owner )
  25         {
  26                 LOG("Waiting");
  27                 Threads_int_Sleep(THREAD_STAT_RWLOCKSLEEP, Lock, 0,
  28                         &Lock->ReaderWaiting, &Lock->ReaderWaitingLast,
  29                         &Lock->Protector);
  30         }
  31         // Ooh, no problems then!
  32         else
  33         {
  34                 Lock->Level++;
  35                 SHORTREL( & Lock->Protector );
  36         }
  37         LOG("Obtained");
  38
  39         return 0;
  40 }
  41
  42 int RWLock_AcquireWrite(tRWLock *Lock)
  43 {
  44         LOG("Acquire RWLock Write %p", Lock);
  45
  46         SHORTLOCK(&Lock->Protector);
  47         if( Lock->Owner || Lock->Level != 0 )
  48         {
  49                 LOG("Waiting");
  50                 Threads_int_Sleep(THREAD_STAT_RWLOCKSLEEP, Lock, 0,
  51                         &Lock->WriterWaiting, &Lock->WriterWaitingLast,
  52                         &Lock->Protector);
  53         }
  54         else
  55         {
  56                 // Nothing else is using the lock, nice :)
  57                 Lock->Owner = Proc_GetCurThread();
  58                 SHORTREL(&Lock->Protector);
  59         }
  60         LOG("Obtained");
  61         return 0;
  62 }
  63
  64 // Release a mutex
  65 void RWLock_Release(tRWLock *Lock)
  66 {
  67         LOG("Release RWLock %p", Lock);
  68         SHORTLOCK( &Lock->Protector );
  69
  70         if( Lock->Owner != Proc_GetCurThread() )
  71                 Lock->Level --;
  72
  73         // Writers first
  74         if( Lock->WriterWaiting )
  75         {
  76                 Lock->Owner = Lock->WriterWaiting;      // Set owner
  77                 Lock->WriterWaiting = Lock->WriterWaiting->Next;        // Next!
  78
  79                 // Wake new owner
  80                 if( Lock->Owner->Status != THREAD_STAT_ACTIVE )
  81                         Threads_AddActive(Lock->Owner);
  82         }
  83         else
  84         {
  85                 Lock->Owner = NULL;
  86
  87                 while( Lock->ReaderWaiting ) {
  88                         Lock->Level ++;
  89                         Threads_AddActive(Lock->ReaderWaiting);
  90                         Lock->ReaderWaiting = Lock->ReaderWaiting->Next;
  91                 }
  92         }
  93         SHORTREL( &Lock->Protector );
  94 }
  95
  96 // === EXPORTS ===
  97 EXPORT(RWLock_AcquireRead);
  98 EXPORT(RWLock_AcquireWrite);
  99 EXPORT(RWLock_Release);