# 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

  internal constants

OPTS

  `GC` build options

### Public Class Methods

add_stress_to_class(class[, ...]) click to toggle source

Raises `NoMemoryError` when allocating an instance of the given classes.

    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;
    }

compact() click to toggle source

    # File gc.rb, line 158
    def self.compact
      __builtin_rb_gc_compact
    end

count → Integer click to toggle source

The number of times `GC` occurred.

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

    # File gc.rb, line 99
    def self.count
      __builtin_gc_count
    end

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

    # File gc.rb, line 63
    def self.disable
      __builtin_gc_disable
    end

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

    # File gc.rb, line 51
    def self.enable
      __builtin_gc_enable
    end

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.

    # File gc.rb, line 154
    def self.latest_gc_info hash_or_key = nil
      __builtin_gc_latest_gc_info hash_or_key
    end

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(class[, ...]) click to toggle source

No longer raises `NoMemoryError` when allocating an instance of the given classes.

    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
garbage_collect → nil
include GC; garbage_collect → nil
start(full_mark: true, immediate_sweep: true) → nil
garbage_collect(full_mark: true, immediate_sweep: true) → nil
include GC; garbage_collect(full_mark: true, immediate_sweep: true) → nil

Initiates garbage collection, even if 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.

    # File gc.rb, line 33
    def self.start full_mark: true, immediate_mark: true, immediate_sweep: true
      __builtin_gc_start_internal full_mark, immediate_mark, immediate_sweep
    end

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.

    # File gc.rb, line 144
    def self.stat hash_or_key = nil
      __builtin_gc_stat hash_or_key
    end

stress → integer, true or false click to toggle source

Returns current status of `GC` stress mode.

    # File gc.rb, line 71
    def self.stress
      __builtin_gc_stress_get
    end

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

    # File gc.rb, line 89
    def self.stress=(flag)
      __builtin_gc_stress_set_m flag
    end

verify_compaction_references(toward: nil, double_heap: nil) → nil click to toggle source

Verify compaction reference consistency.

This method is implementation specific. During compaction, objects that were moved are replaced with T_MOVED objects. No object should have a reference to a T_MOVED object after compaction.

This function doubles the heap to ensure room to move all objects, compacts the heap to make sure everything moves, updates all references, then performs a full `GC`. If any object contains a reference to a T_MOVED object, that object should be pushed on the mark stack, and will make a SEGV.

    static VALUE
    gc_verify_compaction_references(int argc, VALUE *argv, VALUE mod)
    {
        rb_objspace_t *objspace = &rb_objspace;
        int use_toward_empty = FALSE;
        int use_double_pages = FALSE;

        if (dont_gc) return Qnil;

        VALUE opt = Qnil;
        static ID keyword_ids[2];
        VALUE kwvals[2];

        kwvals[1] = Qtrue;

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

        if (!NIL_P(opt)) {
            if (!keyword_ids[0]) {
                keyword_ids[0] = rb_intern("toward");
                keyword_ids[1] = rb_intern("double_heap");
            }

            rb_get_kwargs(opt, keyword_ids, 0, 2, kwvals);
            if (kwvals[0] != Qundef && rb_intern("empty") == rb_sym2id(kwvals[0])) {
                use_toward_empty = TRUE;
            }
            if (kwvals[1] != Qundef && RTEST(kwvals[1])) {
                use_double_pages = TRUE;
            }
        }

        gc_compact(objspace, use_toward_empty, use_double_pages, TRUE);
        return gc_compact_stats(objspace);
    }

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_m(VALUE dummy)
    {
        gc_verify_internal_consistency(&rb_objspace);

        return Qnil;
    }

verify_transient_heap_internal_consistency() click to toggle source

    static VALUE
    gc_verify_transient_heap_internal_consistency(VALUE dmy)
    {
        rb_transient_heap_verify();
        return Qnil;
    }

### Public Instance Methods

garbage_collect(full_mark: true, immediate_mark: true, immediate_sweep: true) click to toggle source

    # File gc.rb, line 37
    def garbage_collect full_mark: true, immediate_mark: true, immediate_sweep: true
      __builtin_gc_start_internal full_mark, immediate_mark, immediate_sweep
    end