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 #if !defined(SMP)
  26 Capability MainCapability;     /* for non-SMP, we have one global capability */
  27 #endif
  28
  29 static
  30 void
  31 initCapability( Capability *cap )
  32 {
  33     cap->f.stgChk0         = (F_)__stg_chk_0;
  34     cap->f.stgChk1         = (F_)__stg_chk_1;
  35     cap->f.stgGCEnter1     = (F_)__stg_gc_enter_1;
  36     cap->f.stgUpdatePAP    = (F_)__stg_update_PAP;
  37 }
  38
  39 #ifdef SMP
  40 static void initCapabilities_(nat n);
  41 #endif
  42
  43 /*
  44  */
  45 void
  46 initCapabilities()
  47 {
  48 #if defined(SMP)
  49   initCapabilities_(RtsFlags.ParFlags.nNodes);
  50 #else
  51   initCapability(&MainCapability);
  52 #endif
  53
  54   return;
  55 }
  56
  57 /* Free capability list.
  58  * Locks required: sched_mutex.
  59  */
  60 #if defined(SMP)
  61 static Capability *free_capabilities; /* Available capabilities for running threads */
  62 #endif
  63
  64 void grabCapability(Capability** cap)
  65 {
  66 #if !defined(SMP)
  67   *cap = &MainCapability;
  68 #else
  69   *cap = free_capabilities;
  70   free_capabilities = (*cap)->link;
  71   rts_n_free_capabilities--;
  72 #endif
  73 }
  74
  75 void releaseCapability(Capability* cap)
  76 {
  77 #if defined(SMP)
  78   cap->link = free_capabilities;
  79   free_capabilities = cap;
  80   rts_n_free_capabilities++;
  81 #endif
  82   return;
  83 }
  84
  85 #if defined(SMP)
  86 /* Allocate 'n' capabilities */
  87 static void
  88 initCapabilities_(nat n)
  89 {
  90   nat i;
  91   Capability *cap, *prev;
  92   cap  = NULL;
  93   prev = NULL;
  94   for (i = 0; i < n; i++) {
  95     cap = stgMallocBytes(sizeof(Capability), "initCapabilities");
  96     initCapability(cap);
  97     cap->link = prev;
  98     prev = cap;
  99   }
 100   free_capabilities = cap;
 101   rts_n_free_capabilities = n;
 102   IF_DEBUG(scheduler,fprintf(stderr,"scheduler: Allocated %d capabilities\n", n_free_capabilities););
 103 }
 104 #endif /* SMP */
 105