ghc/rts/Capability.c

   1 /* ---------------------------------------------------------------------------
   2  *
   3  * (c) The GHC Team, 2001
   4  *
   5  * Capabilities
   6  *
   7  * The notion of a capability is used when operating in multi-threaded
   8  * environments (which the SMP and Threads builds of the RTS do), to
   9  * hold all the state an OS thread/task needs to run Haskell code:
  10  * its STG registers, a pointer to its  TSO, a nursery etc. During
  11  * STG execution, a pointer to the capabilitity is kept in a
  12  * register (BaseReg).
  13  *
  14  * Only in an SMP build will there be multiple capabilities, the threaded
  15  * RTS and other non-threaded builds, there is one global capability,
  16  * namely MainRegTable.
  17  *
  18  *
  19  * --------------------------------------------------------------------------*/
  20 #include "PosixSource.h"
  21 #include "Rts.h"
  22 #include "RtsUtils.h"
  23 #include "Capability.h"
  24
  25
  26 static
  27 void
  28 initCapability( Capability *cap )
  29 {
  30     cap->f.stgChk0         = (F_)__stg_chk_0;
  31     cap->f.stgChk1         = (F_)__stg_chk_1;
  32     cap->f.stgGCEnter1     = (F_)__stg_gc_enter_1;
  33     cap->f.stgUpdatePAP    = (F_)__stg_update_PAP;
  34 }
  35
  36 #ifdef SMP
  37 static void initCapabilities_(nat n);
  38 #endif
  39
  40 /*
  41  */
  42 void
  43 initCapabilities()
  44 {
  45 #if defined(SMP)
  46   initCapabilities_(RtsFlags.ParFlags.nNodes);
  47 #else
  48   initCapability(&MainCapability);
  49 #endif
  50
  51   return;
  52 }
  53
  54 /* Free capability list.
  55  * Locks required: sched_mutex.
  56  */
  57 #if defined(SMP)
  58 static Capability *free_capabilities; /* Available capabilities for running threads */
  59 #endif
  60
  61 void grabCapability(Capability** cap)
  62 {
  63 #if !defined(SMP)
  64   *cap = &MainCapability;
  65 #else
  66   *cap = free_capabilities;
  67   free_capabilities = (*cap)->link;
  68   rts_n_free_capabilities--;
  69 #endif
  70 }
  71
  72 void releaseCapability(Capability** cap)
  73 {
  74 #if defined(SMP)
  75   (*cap)->link = free_capabilities;
  76   free_capabilities = *cap;
  77   rts_n_free_capabilities++;
  78 #endif
  79   return;
  80 }
  81
  82 #if defined(SMP)
  83 /* Allocate 'n' capabilities */
  84 static void
  85 initCapabilities_(nat n)
  86 {
  87   nat i;
  88   Capability *cap, *prev;
  89   cap  = NULL;
  90   prev = NULL;
  91   for (i = 0; i < n; i++) {
  92     cap = stgMallocBytes(sizeof(Capability), "initCapabilities");
  93     initCapability(cap);
  94     cap->link = prev;
  95     prev = cap;
  96   }
  97   free_capabilities = cap;
  98   rts_n_free_capabilities = n;
  99   IF_DEBUG(scheduler,fprintf(stderr,"scheduler: Allocated %d capabilities\n", n_free_capabilities););
 100 }
 101 #endif /* SMP */
 102