# module GC

The GC module provides an interface to Ruby's mark and sweep garbage collection mechanism.

Some of the underlying methods are also available via the ObjectSpace module.

You may obtain information about the operation of the GC through GC::Profiler.

### Constants

INTERNAL_CONSTANTS
OPTS

### Public Class Methods

add_stress_to_class(*args) click to toggle source

    static VALUE
    rb_gcdebug_add_stress_to_class(int argc, VALUE *argv, VALUE self)
    {
        rb_objspace_t *objspace = &rb_objspace;

        if (!stress_to_class) {
            stress_to_class = rb_ary_tmp_new(argc);
        }
        rb_ary_cat(stress_to_class, argv, argc);
        return self;
    }

count → Integer click to toggle source

The number of times GC occurred.

It returns the number of times GC occurred since the process started.

    static VALUE
    gc_count(VALUE self)
    {
        return SIZET2NUM(rb_gc_count());
    }

disable → true or false click to toggle source

Disables garbage collection, returning `true` if garbage collection was already disabled.

    GC.disable   #=> false
    GC.disable   #=> true

    VALUE
    rb_gc_disable(void)
    {
        rb_objspace_t *objspace = &rb_objspace;
        int old = dont_gc;

        gc_rest(objspace);

        dont_gc = TRUE;
        return old ? Qtrue : Qfalse;
    }

enable → true or false click to toggle source

Enables garbage collection, returning `true` if garbage collection was previously disabled.

    GC.disable   #=> false
    GC.enable    #=> true
    GC.enable    #=> false

    VALUE
    rb_gc_enable(void)
    {
        rb_objspace_t *objspace = &rb_objspace;
        int old = dont_gc;

        dont_gc = FALSE;
        return old ? Qtrue : Qfalse;
    }

latest_gc_info -> {:gc_by→:newobj} click to toggle source
latest_gc_info(hash) → hash
latest_gc_info(:major_by) → :malloc

Returns information about the most recent garbage collection.

    static VALUE
    gc_latest_gc_info(int argc, VALUE *argv, VALUE self)
    {
        rb_objspace_t *objspace = &rb_objspace;
        VALUE arg = Qnil;

        if (rb_scan_args(argc, argv, "01", &arg) == 1) {
            if (!SYMBOL_P(arg) && !RB_TYPE_P(arg, T_HASH)) {
                rb_raise(rb_eTypeError, "non-hash or symbol given");
            }
        }

        if (arg == Qnil) {
            arg = rb_hash_new();
        }

        return gc_info_decode(objspace, arg, 0);
    }

malloc_allocated_size → Integer click to toggle source

Returns the size of memory allocated by malloc().

Only available if ruby was built with `CALC_EXACT_MALLOC_SIZE`.

    static VALUE
    gc_malloc_allocated_size(VALUE self)
    {
        return UINT2NUM(rb_objspace.malloc_params.allocated_size);
    }

malloc_allocations → Integer click to toggle source

Returns the number of malloc() allocations.

Only available if ruby was built with `CALC_EXACT_MALLOC_SIZE`.

    static VALUE
    gc_malloc_allocations(VALUE self)
    {
        return UINT2NUM(rb_objspace.malloc_params.allocations);
    }

remove_stress_to_class(*args) click to toggle source

    static VALUE
    rb_gcdebug_remove_stress_to_class(int argc, VALUE *argv, VALUE self)
    {
        rb_objspace_t *objspace = &rb_objspace;
        int i;

        if (stress_to_class) {
            for (i = 0; i < argc; ++i) {
                rb_ary_delete_same(stress_to_class, argv[i]);
            }
            if (RARRAY_LEN(stress_to_class) == 0) {
                stress_to_class = 0;
            }
        }
        return Qnil;
    }

start → nil click to toggle source
start(full_mark: true, immediate_sweep: true) → nil

Initiates garbage collection, unless manually disabled.

This method is defined with keyword arguments that default to true:

    def GC.start(full_mark: true, immediate_sweep: true); end

Use full_mark: false to perform a minor GC. Use immediate_sweep: false to defer sweeping (use lazy sweep).

Note: These keyword arguments are implementation and version dependent. They are not guaranteed to be future-compatible, and may be ignored if the underlying implementation does not support them.

    static VALUE
    gc_start_internal(int argc, VALUE *argv, VALUE self)
    {
        rb_objspace_t *objspace = &rb_objspace;
        int full_mark = TRUE, immediate_mark = TRUE, immediate_sweep = TRUE;
        VALUE opt = Qnil;
        static ID keyword_ids[3];

        rb_scan_args(argc, argv, "0:", &opt);

        if (!NIL_P(opt)) {
            VALUE kwvals[3];

            if (!keyword_ids[0]) {
                keyword_ids[0] = rb_intern("full_mark");
                keyword_ids[1] = rb_intern("immediate_mark");
                keyword_ids[2] = rb_intern("immediate_sweep");
            }

            rb_get_kwargs(opt, keyword_ids, 0, 3, kwvals);

            if (kwvals[0] != Qundef) full_mark = RTEST(kwvals[0]);
            if (kwvals[1] != Qundef) immediate_mark = RTEST(kwvals[1]);
            if (kwvals[2] != Qundef) immediate_sweep = RTEST(kwvals[2]);
        }

        garbage_collect(objspace, full_mark, immediate_mark, immediate_sweep, GPR_FLAG_METHOD);
        gc_finalize_deferred(objspace);

        return Qnil;
    }

stat → Hash click to toggle source
stat(hash) → hash
stat(:key) → Numeric

Returns a Hash containing information about the GC.

The hash includes information about internal statistics about GC such as:

    {
        :count=>0,
        :heap_allocated_pages=>24,
        :heap_sorted_length=>24,
        :heap_allocatable_pages=>0,
        :heap_available_slots=>9783,
        :heap_live_slots=>7713,
        :heap_free_slots=>2070,
        :heap_final_slots=>0,
        :heap_marked_slots=>0,
        :heap_eden_pages=>24,
        :heap_tomb_pages=>0,
        :total_allocated_pages=>24,
        :total_freed_pages=>0,
        :total_allocated_objects=>7796,
        :total_freed_objects=>83,
        :malloc_increase_bytes=>2389312,
        :malloc_increase_bytes_limit=>16777216,
        :minor_gc_count=>0,
        :major_gc_count=>0,
        :remembered_wb_unprotected_objects=>0,
        :remembered_wb_unprotected_objects_limit=>0,
        :old_objects=>0,
        :old_objects_limit=>0,
        :oldmalloc_increase_bytes=>2389760,
        :oldmalloc_increase_bytes_limit=>16777216
    }

The contents of the hash are implementation specific and may be changed in the future.

This method is only expected to work on C Ruby.

    static VALUE
    gc_stat(int argc, VALUE *argv, VALUE self)
    {
        VALUE arg = Qnil;

        if (rb_scan_args(argc, argv, "01", &arg) == 1) {
            if (SYMBOL_P(arg)) {
                size_t value = gc_stat_internal(arg);
                return SIZET2NUM(value);
            }
            else if (!RB_TYPE_P(arg, T_HASH)) {
                rb_raise(rb_eTypeError, "non-hash or symbol given");
            }
        }

        if (arg == Qnil) {
            arg = rb_hash_new();
        }
        gc_stat_internal(arg);
        return arg;
    }

stress → integer, true or false click to toggle source

Returns current status of GC stress mode.

    static VALUE
    gc_stress_get(VALUE self)
    {
        rb_objspace_t *objspace = &rb_objspace;
        return ruby_gc_stress_mode;
    }

stress = flag → flag click to toggle source

Updates the GC stress mode.

When stress mode is enabled, the GC is invoked at every GC opportunity: all memory and object allocations.

Enabling stress mode will degrade performance, it is only for debugging.

flag can be true, false, or an integer bit-ORed following flags.

    0x01:: no major GC
    0x02:: no immediate sweep
    0x04:: full mark after malloc/calloc/realloc

    static VALUE
    gc_stress_set_m(VALUE self, VALUE flag)
    {
        rb_objspace_t *objspace = &rb_objspace;
        gc_stress_set(objspace, flag);
        return flag;
    }

verify_internal_consistency → nil click to toggle source

Verify internal consistency.

This method is implementation specific. Now this method checks generational consistency if RGenGC is supported.

    static VALUE
    gc_verify_internal_consistency(VALUE dummy)
    {
        rb_objspace_t *objspace = &rb_objspace;
        struct verify_internal_consistency_struct data = {0};
        struct each_obj_args eo_args;

        data.objspace = objspace;
        gc_report(5, objspace, "gc_verify_internal_consistency: start\n");

        /* check relations */

        eo_args.callback = verify_internal_consistency_i;
        eo_args.data = (void *)&data;
        objspace_each_objects((VALUE)&eo_args);

        if (data.err_count != 0) {
    #if RGENGC_CHECK_MODE >= 5
            objspace->rgengc.error_count = data.err_count;
            gc_marks_check(objspace, NULL, NULL);
            allrefs_dump(objspace);
    #endif
            rb_bug("gc_verify_internal_consistency: found internal inconsistency.");
        }

        /* check heap_page status */
        gc_verify_heap_pages(objspace);

        /* check counters */

        if (!is_lazy_sweeping(heap_eden) && !finalizing) {
            if (objspace_live_slots(objspace) != data.live_object_count) {
                fprintf(stderr, "heap_pages_final_slots: %d, objspace->profile.total_freed_objects: %d\n",
                        (int)heap_pages_final_slots, (int)objspace->profile.total_freed_objects);
                rb_bug("inconsistent live slot number: expect %"PRIuSIZE", but %"PRIuSIZE".", objspace_live_slots(objspace), data.live_object_count);
            }
        }

    #if USE_RGENGC
        if (!is_marking(objspace)) {
            if (objspace->rgengc.old_objects != data.old_object_count) {
                rb_bug("inconsistent old slot number: expect %"PRIuSIZE", but %"PRIuSIZE".", objspace->rgengc.old_objects, data.old_object_count);
            }
            if (objspace->rgengc.uncollectible_wb_unprotected_objects != data.remembered_shady_count) {
                rb_bug("inconsistent old slot number: expect %"PRIuSIZE", but %"PRIuSIZE".", objspace->rgengc.uncollectible_wb_unprotected_objects, data.remembered_shady_count);
            }
        }
    #endif

        if (!finalizing) {
            size_t list_count = 0;

            {
                VALUE z = heap_pages_deferred_final;
                while (z) {
                    list_count++;
                    z = RZOMBIE(z)->next;
                }
            }

            if (heap_pages_final_slots != data.zombie_object_count ||
                heap_pages_final_slots != list_count) {

                rb_bug("inconsistent finalizing object count:\n"
                       "  expect %"PRIuSIZE"\n"
                       "  but    %"PRIuSIZE" zombies\n"
                       "  heap_pages_deferred_final list has %"PRIuSIZE" items.",
                       heap_pages_final_slots,
                       data.zombie_object_count,
                       list_count);
            }
        }

        gc_report(5, objspace, "gc_verify_internal_consistency: OK\n");

        return Qnil;
    }

### Public Instance Methods

garbage_collect → nil click to toggle source
include GC; garbage_collect → nil
garbage_collect(full_mark: true, immediate_sweep: true) → nil

Initiates garbage collection, unless manually disabled.

This method is defined with keyword arguments that default to true:

    def GC.start(full_mark: true, immediate_sweep: true); end

Use full_mark: false to perform a minor GC. Use immediate_sweep: false to defer sweeping (use lazy sweep).

Note: These keyword arguments are implementation and version dependent. They are not guaranteed to be future-compatible, and may be ignored if the underlying implementation does not support them.

    static VALUE
    gc_start_internal(int argc, VALUE *argv, VALUE self)
    {
        rb_objspace_t *objspace = &rb_objspace;
        int full_mark = TRUE, immediate_mark = TRUE, immediate_sweep = TRUE;
        VALUE opt = Qnil;
        static ID keyword_ids[3];

        rb_scan_args(argc, argv, "0:", &opt);

        if (!NIL_P(opt)) {
            VALUE kwvals[3];

            if (!keyword_ids[0]) {
                keyword_ids[0] = rb_intern("full_mark");
                keyword_ids[1] = rb_intern("immediate_mark");
                keyword_ids[2] = rb_intern("immediate_sweep");
            }

            rb_get_kwargs(opt, keyword_ids, 0, 3, kwvals);

            if (kwvals[0] != Qundef) full_mark = RTEST(kwvals[0]);
            if (kwvals[1] != Qundef) immediate_mark = RTEST(kwvals[1]);
            if (kwvals[2] != Qundef) immediate_sweep = RTEST(kwvals[2]);
        }

        garbage_collect(objspace, full_mark, immediate_mark, immediate_sweep, GPR_FLAG_METHOD);
        gc_finalize_deferred(objspace);

        return Qnil;
    }