GC.h

/* -----------------------------------------------------------------------------
 *
 * (c) The GHC Team, 1998-2004
 *
 * External Storage Manger Interface
 *
 * ---------------------------------------------------------------------------*/

#ifndef RTS_STORAGE_GC_H
#define RTS_STORAGE_GC_H

#include <stddef.h>
#include "rts/OSThreads.h"

/* -----------------------------------------------------------------------------
 * Generational GC
 *
 * We support an arbitrary number of generations, with an arbitrary number
 * of steps per generation.  Notes (in no particular order):
 *
 *       - all generations except the oldest should have the same
 *         number of steps.  Multiple steps gives objects a decent
 *         chance to age before being promoted, and helps ensure that
 *         we don't end up with too many thunks being updated in older
 *         generations.
 *
 *       - the oldest generation has one step.  There's no point in aging
 *         objects in the oldest generation.
 *
 *       - generation 0, step 0 (G0S0) is the allocation area.  It is given
 *         a fixed set of blocks during initialisation, and these blocks
 *         normally stay in G0S0.  In parallel execution, each
 *         Capability has its own nursery.
 *
 *       - during garbage collection, each step which is an evacuation
 *         destination (i.e. all steps except G0S0) is allocated a to-space.
 *         evacuated objects are allocated into the step's to-space until
 *         GC is finished, when the original step's contents may be freed
 *         and replaced by the to-space.
 *
 *       - the mutable-list is per-generation (not per-step).  G0 doesn't 
 *         have one (since every garbage collection collects at least G0).
 * 
 *       - block descriptors contain pointers to both the step and the
 *         generation that the block belongs to, for convenience.
 *
 *       - static objects are stored in per-generation lists.  See GC.c for
 *         details of how we collect CAFs in the generational scheme.
 *
 *       - large objects are per-step, and are promoted in the same way
 *         as small objects, except that we may allocate large objects into
 *         generation 1 initially.
 *
 * ------------------------------------------------------------------------- */

typedef struct nursery_ {
    bdescr *       blocks;
    unsigned int   n_blocks;
} nursery;

typedef struct generation_ {
    unsigned int   no;			// generation number

    bdescr *       blocks;	        // blocks in this gen
    unsigned int   n_blocks;	        // number of blocks
    unsigned int   n_words;             // number of words

    bdescr *       large_objects;	// large objects (doubly linked)
    unsigned int   n_large_blocks;      // no. of blocks used by large objs
    unsigned int   n_new_large_blocks;  // count freshly allocated large objects

    unsigned int   max_blocks;		// max blocks
    bdescr        *mut_list;      	// mut objects in this gen (not G0)

    StgTSO *       threads;             // threads in this gen
                                        // linked via global_link
    struct generation_ *to;		// destination gen for live objects

    // stats information
    unsigned int collections;
    unsigned int par_collections;
    unsigned int failed_promotions;

    // ------------------------------------
    // Fields below are used during GC only

#if defined(THREADED_RTS)
    char pad[128];                      // make sure the following is
                                        // on a separate cache line.
    SpinLock     sync_large_objects;    // lock for large_objects
                                        //    and scavenged_large_objects
#endif

    int          mark;			// mark (not copy)? (old gen only)
    int          compact;		// compact (not sweep)? (old gen only)

    // During GC, if we are collecting this gen, blocks and n_blocks
    // are copied into the following two fields.  After GC, these blocks
    // are freed.
    bdescr *     old_blocks;	        // bdescr of first from-space block
    unsigned int n_old_blocks;		// number of blocks in from-space
    unsigned int live_estimate;         // for sweeping: estimate of live data
    
    bdescr *     saved_mut_list;

    bdescr *     part_blocks;           // partially-full scanned blocks
    unsigned int n_part_blocks;         // count of above

    bdescr *     scavenged_large_objects;  // live large objs after GC (d-link)
    unsigned int n_scavenged_large_blocks; // size (not count) of above

    bdescr *     bitmap;  		// bitmap for compacting collection

    StgTSO *     old_threads;
} generation;

extern generation * generations;
extern generation * g0;
extern generation * oldest_gen;

/* -----------------------------------------------------------------------------
   Generic allocation

   StgPtr allocate(Capability *cap, nat n)
                                Allocates memory from the nursery in
				the current Capability.  This can be
				done without taking a global lock,
                                unlike allocate().

   StgPtr allocatePinned(Capability *cap, nat n) 
                                Allocates a chunk of contiguous store
   				n words long, which is at a fixed
				address (won't be moved by GC).  
				Returns a pointer to the first word.
				Always succeeds.
				
				NOTE: the GC can't in general handle
				pinned objects, so allocatePinned()
				can only be used for ByteArrays at the
				moment.

				Don't forget to TICK_ALLOC_XXX(...)
				after calling allocate or
				allocatePinned, for the
				benefit of the ticky-ticky profiler.

   -------------------------------------------------------------------------- */

StgPtr  allocate        ( Capability *cap, lnat n );
StgPtr  allocatePinned  ( Capability *cap, lnat n );

/* memory allocator for executable memory */
void * allocateExec(unsigned int len, void **exec_addr);
void   freeExec (void *p);

// Used by GC checks in external .cmm code:
extern nat alloc_blocks_lim;

/* -----------------------------------------------------------------------------
   Performing Garbage Collection
   -------------------------------------------------------------------------- */

void performGC(void);
void performMajorGC(void);

/* -----------------------------------------------------------------------------
   The CAF table - used to let us revert CAFs in GHCi
   -------------------------------------------------------------------------- */

void newCAF     (StgRegTable *reg, StgClosure *);
void newDynCAF  (StgRegTable *reg, StgClosure *);
void revertCAFs (void);

/* -----------------------------------------------------------------------------
   This is the write barrier for MUT_VARs, a.k.a. IORefs.  A
   MUT_VAR_CLEAN object is not on the mutable list; a MUT_VAR_DIRTY
   is.  When written to, a MUT_VAR_CLEAN turns into a MUT_VAR_DIRTY
   and is put on the mutable list.
   -------------------------------------------------------------------------- */

void dirty_MUT_VAR(StgRegTable *reg, StgClosure *p);

/* set to disable CAF garbage collection in GHCi. */
/* (needed when dynamic libraries are used). */
extern rtsBool keepCAFs;

INLINE_HEADER void initBdescr(bdescr *bd, generation *gen, generation *dest)
{
    bd->gen    = gen;
    bd->gen_no = gen->no;
    bd->dest   = dest;
}

#endif /* RTS_STORAGE_GC_H */