guile/bdw.c

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "gc-api.h"
#include "gc-ephemeron.h"

#define GC_IMPL 1
#include "gc-internal.h"

#include "bdw-attrs.h"

#if GC_PRECISE_ROOTS
#error bdw-gc is a conservative collector
#endif

#if !GC_CONSERVATIVE_ROOTS
#error bdw-gc is a conservative collector
#endif

#if !GC_CONSERVATIVE_TRACE
#error bdw-gc is a conservative collector
#endif

// When pthreads are used, let `libgc' know about it and redirect
// allocation calls such as `GC_MALLOC ()' to (contention-free, faster)
// thread-local allocation.

#define GC_THREADS 1
#define GC_REDIRECT_TO_LOCAL 1

// Don't #define pthread routines to their GC_pthread counterparts.
// Instead we will be careful inside the benchmarks to use API to
// register threads with libgc.
#define GC_NO_THREAD_REDIRECTS 1

#include <gc/gc.h>
#include <gc/gc_inline.h> /* GC_generic_malloc_many */
#include <gc/gc_mark.h> /* GC_generic_malloc */

#define GC_INLINE_GRANULE_WORDS 2
#define GC_INLINE_GRANULE_BYTES (sizeof(void *) * GC_INLINE_GRANULE_WORDS)

/* A freelist set contains GC_INLINE_FREELIST_COUNT pointers to singly
   linked lists of objects of different sizes, the ith one containing
   objects i + 1 granules in size.  This setting of
   GC_INLINE_FREELIST_COUNT will hold freelists for allocations of
   up to 256 bytes.  */
#define GC_INLINE_FREELIST_COUNT (256U / GC_INLINE_GRANULE_BYTES)

struct gc_heap {
  pthread_mutex_t lock;
  int multithreaded;
};

struct gc_mutator {
  void *freelists[GC_INLINE_FREELIST_COUNT];
  struct gc_heap *heap;
};

static inline size_t gc_inline_bytes_to_freelist_index(size_t bytes) {
  return (bytes - 1U) / GC_INLINE_GRANULE_BYTES;
}
static inline size_t gc_inline_freelist_object_size(size_t idx) {
  return (idx + 1U) * GC_INLINE_GRANULE_BYTES;
}

// The values of these must match the internal POINTERLESS and NORMAL
// definitions in libgc, for which unfortunately there are no external
// definitions.  Alack.
enum gc_inline_kind {
  GC_INLINE_KIND_POINTERLESS,
  GC_INLINE_KIND_NORMAL
};

static inline void *
allocate_small(void **freelist, size_t idx, enum gc_inline_kind kind) {
  void *head = *freelist;

  if (!head) {
    size_t bytes = gc_inline_freelist_object_size(idx);
    GC_generic_malloc_many(bytes, kind, freelist);
    head = *freelist;
    if (GC_UNLIKELY (!head)) {
      fprintf(stderr, "ran out of space, heap size %zu\n",
              GC_get_heap_size());
      GC_CRASH();
    }
  }

  *freelist = *(void **)(head);
  return head;
}

void* gc_allocate_slow(struct gc_mutator *mut, size_t size) {
  GC_ASSERT(size != 0);
  if (size <= gc_allocator_large_threshold()) {
    size_t idx = gc_inline_bytes_to_freelist_index(size);
    return allocate_small(&mut->freelists[idx], idx, GC_INLINE_KIND_NORMAL);
  } else {
    return GC_malloc(size);
  }
}

void* gc_allocate_pointerless(struct gc_mutator *mut,
                                            size_t size) {
  // Because the BDW API requires us to implement a custom marker so
  // that the pointerless freelist gets traced, even though it's in a
  // pointerless region, we punt on thread-local pointerless freelists.
  return GC_malloc_atomic(size);
}

void gc_collect(struct gc_mutator *mut) {
  GC_gcollect();
}

void gc_write_barrier_extern(struct gc_ref obj, size_t obj_size,
                             struct gc_edge edge, struct gc_ref new_val) {
}

// In BDW-GC, we can't hook into the mark phase to call
// gc_trace_ephemerons_for_object, so the advertised ephemeron strategy
// doesn't really work.  The primitives that we have are mark functions,
// which run during GC and can't allocate; finalizers, which run after
// GC and can allocate but can't add to the connectivity graph; and
// disappearing links, which are cleared at the end of marking, in the
// stop-the-world phase.  It does not appear to be possible to implement
// ephemerons using these primitives.  Instead fall back to weak-key
// tables.

static int ephemeron_gc_kind;

struct gc_ref gc_allocate_ephemeron(struct gc_mutator *mut) {
  void *ret = GC_generic_malloc(gc_ephemeron_size(), ephemeron_gc_kind);
  return gc_ref_from_heap_object(ret);
}

unsigned gc_heap_ephemeron_trace_epoch(struct gc_heap *heap) {
  return 0;
}

void gc_ephemeron_init(struct gc_mutator *mut, struct gc_ephemeron *ephemeron,
                       struct gc_ref key, struct gc_ref value) {
  gc_ephemeron_init_internal(mut->heap, ephemeron, key, value);
  if (GC_base((void*)gc_ref_value(key))) {
    struct gc_ref *loc = gc_edge_loc(gc_ephemeron_key_edge(ephemeron));
    GC_register_disappearing_link((void**)loc);
  }
}

struct ephemeron_mark_state {
  struct GC_ms_entry *mark_stack_ptr;
  struct GC_ms_entry *mark_stack_limit;
};

int gc_visit_ephemeron_key(struct gc_edge edge, struct gc_heap *heap) {
  // Pretend the key is traced, to avoid adding this ephemeron to the
  // global table.
  return 1;
}
static void trace_ephemeron_edge(struct gc_edge edge, struct gc_heap *heap,
                                 void *visit_data) {
  struct ephemeron_mark_state *state = visit_data;
  uintptr_t addr = gc_ref_value(gc_edge_ref(edge));
  state->mark_stack_ptr = GC_MARK_AND_PUSH ((void *) addr,
                                            state->mark_stack_ptr,
                                            state->mark_stack_limit,
                                            NULL);
}

static struct GC_ms_entry *
mark_ephemeron(GC_word *addr, struct GC_ms_entry *mark_stack_ptr,
               struct GC_ms_entry *mark_stack_limit, GC_word env) {

  struct ephemeron_mark_state state = {
    mark_stack_ptr,
    mark_stack_limit,
  };
  
  struct gc_ephemeron *ephemeron = (struct gc_ephemeron*) addr;

  // If this ephemeron is on a freelist, its first word will be a
  // freelist link and everything else will be NULL.
  if (!gc_ref_value(gc_edge_ref(gc_ephemeron_value_edge(ephemeron)))) {
    trace_ephemeron_edge(gc_edge(addr), NULL, &state);
    return state.mark_stack_ptr;
  }

  if (!gc_ref_value(gc_edge_ref(gc_ephemeron_key_edge(ephemeron)))) {
    // If the key died in a previous collection, the disappearing link
    // will have been cleared.  Mark the ephemeron as dead.
    gc_ephemeron_mark_dead(ephemeron);
  }

  gc_trace_ephemeron(ephemeron, trace_ephemeron_edge, NULL, &state);

  return state.mark_stack_ptr;
}

static inline struct gc_mutator *add_mutator(struct gc_heap *heap) {
  struct gc_mutator *ret = GC_malloc(sizeof(struct gc_mutator));
  ret->heap = heap;
  return ret;
}

static inline struct gc_heap *mutator_heap(struct gc_mutator *mutator) {
  return mutator->heap;
}

struct gc_options {
  struct gc_common_options common;
};
int gc_option_from_string(const char *str) {
  return gc_common_option_from_string(str);
}
struct gc_options* gc_allocate_options(void) {
  struct gc_options *ret = malloc(sizeof(struct gc_options));
  gc_init_common_options(&ret->common);
  return ret;
}
int gc_options_set_int(struct gc_options *options, int option, int value) {
  return gc_common_options_set_int(&options->common, option, value);
}
int gc_options_set_size(struct gc_options *options, int option,
                        size_t value) {
  return gc_common_options_set_size(&options->common, option, value);
}
int gc_options_set_double(struct gc_options *options, int option,
                          double value) {
  return gc_common_options_set_double(&options->common, option, value);
}
int gc_options_parse_and_set(struct gc_options *options, int option,
                             const char *value) {
  return gc_common_options_parse_and_set(&options->common, option, value);
}

int gc_init(const struct gc_options *options, struct gc_stack_addr *stack_base,
            struct gc_heap **heap, struct gc_mutator **mutator) {
  GC_ASSERT_EQ(gc_allocator_small_granule_size(), GC_INLINE_GRANULE_BYTES);
  GC_ASSERT_EQ(gc_allocator_large_threshold(),
               GC_INLINE_FREELIST_COUNT * GC_INLINE_GRANULE_BYTES);

  if (!options) options = gc_allocate_options();

  // Ignore stack base for main thread.

  switch (options->common.heap_size_policy) {
    case GC_HEAP_SIZE_FIXED:
      GC_set_max_heap_size(options->common.heap_size);
      break;
    case GC_HEAP_SIZE_GROWABLE: {
      if (options->common.maximum_heap_size)
        GC_set_max_heap_size(options->common.maximum_heap_size);
      // BDW uses a pretty weird heap-sizing heuristic:
      //
      // heap-size = live-data * (1 + (2 / GC_free_space_divisor))
      // heap-size-multiplier = heap-size/live-data = 1 + 2/GC_free_space_divisor
      // GC_free_space_divisor = 2/(heap-size-multiplier-1)
      //
      // (Assumption: your heap is mostly "composite", i.e. not
      // "atomic".  See bdw's alloc.c:min_bytes_allocd.)
      double fsd = 2.0/(options->common.heap_size_multiplier - 1);
      // But, the divisor is an integer.  WTF.  This caps the effective
      // maximum heap multiplier at 3.  Oh well.
      GC_set_free_space_divisor(fsd + 0.51);
      break;
    }
    case GC_HEAP_SIZE_ADAPTIVE:
    default:
      fprintf(stderr, "adaptive heap sizing unsupported by bdw-gc\n");
      return 0;
  }

  // Not part of 7.3, sigh.  Have to set an env var.
  // GC_set_markers_count(options->common.parallelism);
  char markers[21] = {0,}; // 21 bytes enough for 2**64 in decimal + NUL.
  snprintf(markers, sizeof(markers), "%d", options->common.parallelism);
  setenv("GC_MARKERS", markers, 1);
  GC_init();
  size_t current_heap_size = GC_get_heap_size();
  if (options->common.heap_size > current_heap_size)
    GC_expand_hp(options->common.heap_size - current_heap_size);
  GC_allow_register_threads();
  *heap = GC_malloc(sizeof(struct gc_heap));
  pthread_mutex_init(&(*heap)->lock, NULL);
  *mutator = add_mutator(*heap);

  {
    GC_word descriptor = GC_MAKE_PROC(GC_new_proc(mark_ephemeron), 0);
    int add_size_to_descriptor = 0;
    int clear_memory = 1;
    ephemeron_gc_kind = GC_new_kind(GC_new_free_list(), descriptor,
                                    add_size_to_descriptor, clear_memory);
  }

  return 1;
}

struct gc_mutator* gc_init_for_thread(struct gc_stack_addr *stack_base,
                                      struct gc_heap *heap) {
  pthread_mutex_lock(&heap->lock);
  if (!heap->multithreaded) {
    GC_allow_register_threads();
    heap->multithreaded = 1;
  }
  pthread_mutex_unlock(&heap->lock);

  struct GC_stack_base base = { stack_base };
  GC_register_my_thread(&base);
  return add_mutator(heap);
}
void gc_finish_for_thread(struct gc_mutator *mut) {
  GC_unregister_my_thread();
}

void* gc_call_without_gc(struct gc_mutator *mut,
                         void* (*f)(void*),
                         void *data) {
  return GC_do_blocking(f, data);
}

void gc_mutator_set_roots(struct gc_mutator *mut,
                          struct gc_mutator_roots *roots) {
}
void gc_heap_set_roots(struct gc_heap *heap, struct gc_heap_roots *roots) {
}

void gc_print_stats(struct gc_heap *heap) {
  printf("Completed %ld collections\n", (long)GC_get_gc_no());
  printf("Heap size is %ld\n", (long)GC_get_heap_size());
}