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         // - OR, there's a writer waiting to write
  25         if( Lock->Owner || Lock->WriterWaiting )
  26         {
  27                 LOG("Waiting");
  28                 Threads_int_Sleep(THREAD_STAT_RWLOCKSLEEP, Lock, 0,
  29                         &Lock->ReaderWaiting, &Lock->ReaderWaitingLast,
  30                         &Lock->Protector);
  31         }
  32         // Ooh, no problems then!
  33         else
  34         {
  35                 Lock->Level++;
  36                 SHORTREL( & Lock->Protector );
  37         }
  38         LOG("Obtained");
  39
  40         return 0;
  41 }
  42
  43 int RWLock_AcquireWrite(tRWLock *Lock)
  44 {
  45         LOG("Acquire RWLock Write %p", Lock);
  46
  47         SHORTLOCK(&Lock->Protector);
  48         if( Lock->Owner || Lock->Level != 0 )
  49         {
  50                 LOG("Waiting");
  51                 Threads_int_Sleep(THREAD_STAT_RWLOCKSLEEP, Lock, 0,
  52                         &Lock->WriterWaiting, &Lock->WriterWaitingLast,
  53                         &Lock->Protector);
  54         }
  55         else
  56         {
  57                 // Nothing else is using the lock, nice :)
  58                 Lock->Owner = Proc_GetCurThread();
  59                 SHORTREL(&Lock->Protector);
  60         }
  61         LOG("Obtained");
  62         return 0;
  63 }
  64
  65 // Release a mutex
  66 void RWLock_Release(tRWLock *Lock)
  67 {
  68         LOG("Release RWLock %p", Lock);
  69         SHORTLOCK( &Lock->Protector );
  70
  71         if( Lock->Owner != Proc_GetCurThread() )
  72                 Lock->Level --;
  73
  74         // Writers first
  75         if( Lock->WriterWaiting )
  76         {
  77                 Lock->Owner = Lock->WriterWaiting;      // Set owner
  78                 Lock->WriterWaiting = Lock->WriterWaiting->Next;        // Next!
  79
  80                 // Wake new owner
  81                 if( Lock->Owner->Status != THREAD_STAT_ACTIVE )
  82                         Threads_AddActive(Lock->Owner);
  83         }
  84         else
  85         {
  86                 Lock->Owner = NULL;
  87
  88                 while( Lock->ReaderWaiting ) {
  89                         Lock->Level ++;
  90                         Threads_AddActive(Lock->ReaderWaiting);
  91                         Lock->ReaderWaiting = Lock->ReaderWaiting->Next;
  92                 }
  93         }
  94         SHORTREL( &Lock->Protector );
  95 }
  96
  97 // === EXPORTS ===
  98 EXPORT(RWLock_AcquireRead);
  99 EXPORT(RWLock_AcquireWrite);
 100 EXPORT(RWLock_Release);