Module: GC

Relationships & Source Files
Namespace Children
Modules: `Profiler`
Defined in:	gc.rb, gc.c

Overview

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 Profiler.

Constant Summary

INTERNAL_CONSTANTS =

Internal constants in the garbage collector.

# File 'gc.c', line 14328
```
gc_constants
```
OPTS =

GC build options

# File 'gc.c', line 14386
```
opts = rb_ary_new()
```

Class Attribute Summary

.auto_compact ⇒ Boolean rw

Returns whether or not automatic compaction has been enabled.
.auto_compact=(flag) rw

Updates automatic compaction mode.
.measure_total_time ⇒ Boolean rw

Return measure_total_time flag (default: true).
.measure_total_time=(true/false) rw

Enable to measure GC time.
.stress ⇒ Boolean rw

Returns current status of GC stress mode.
.stress=(flag) ⇒ flag rw

Updates the GC stress mode.

Class Method Summary

.add_stress_to_class(class[, ...])

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

This function compacts objects together in Ruby’s heap.
.count ⇒ Integer

The number of times GC occurred.
.disable ⇒ Boolean

Disables garbage collection, returning true if garbage collection was already disabled.
.enable ⇒ Boolean

Enables garbage collection, returning true if garbage collection was previously disabled.
.latest_compact_info ⇒ Hash

Returns information about object moved in the most recent GC compaction.
.latest_gc_info ⇒ Hash

Returns information about the most recent garbage collection.
.malloc_allocated_size ⇒ Integer

Returns the size of memory allocated by malloc().
.malloc_allocations ⇒ Integer

Returns the number of malloc() allocations.
.remove_stress_to_class(class[, ...])

No longer raises ::NoMemoryError when allocating an instance of the given classes.
.start(full_mark: true, immediate_mark: true, immediate_sweep: true)

Initiates garbage collection, even if manually disabled.
.stat ⇒ Hash

Returns a ::Hash containing information about the GC.
.stat_heap ⇒ Hash

Returns information for heaps in the GC.
.total_time ⇒ Integer

Return measured GC total time in nano seconds.
.verify_compaction_references(toward: nil, double_heap: false) ⇒ Hash

Verify compaction reference consistency.
.verify_internal_consistency ⇒ nil

Verify internal consistency.

Instance Method Summary

#garbage_collect(full_mark: true, immediate_mark: true, immediate_sweep: true)

Alias of .start

Class Attribute Details

.auto_compact ⇒ `Boolean` (rw)

Returns whether or not automatic compaction has been enabled.

[ GitHub ]

# File 'gc.c', line 11926


static VALUE
gc_get_auto_compact(VALUE _)
{
    return RBOOL(ruby_enable_autocompact);
}

.auto_compact=(flag) (rw)

Updates automatic compaction mode.

When enabled, the compactor will execute on every major collection.

Enabling compaction will degrade performance on major collections.

[ GitHub ]

# File 'gc.c', line 11895


static VALUE
gc_set_auto_compact(VALUE _, VALUE v)
{
    GC_ASSERT(GC_COMPACTION_SUPPORTED);

    ruby_enable_autocompact = RTEST(v);

#if RGENGC_CHECK_MODE
    ruby_autocompact_compare_func = NULL;

    if (SYMBOL_P(v)) {
        ID id = RB_SYM2ID(v);
        if (id == rb_intern("empty")) {
            ruby_autocompact_compare_func = compare_free_slots;
        }
    }
#endif

    return v;
}

.measure_total_time ⇒ `Boolean` (rw)

Return measure_total_time flag (default: true). Note that measurement can affect the application performance.

[ GitHub ]

# File 'gc.rb', line 308


def self.measure_total_time
  Primitive.cexpr! %{
    RBOOL(rb_objspace.flags.measure_gc)
  }
end

.measure_total_time=(true/false) (rw)

Enable to measure GC time. You can get the result with GC.stat(:time). Note that GC time measurement can cause some performance overhead.

[ GitHub ]

# File 'gc.rb', line 296


def self.measure_total_time=(flag)
  Primitive.cstmt! %{
    rb_objspace.flags.measure_gc = RTEST(flag) ? TRUE : FALSE;
    return flag;
  }
end

.stress ⇒ `Boolean` (rw)

Returns current status of GC stress mode.

[ GitHub ]

# File 'gc.rb', line 77


def self.stress
  Primitive.gc_stress_get
end

.stress=(flag) ⇒ `flag` (rw)

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

[ GitHub ]

# File 'gc.rb', line 95


def self.stress=(flag)
  Primitive.gc_stress_set_m flag
end

Class Method Details

.add_stress_to_class(class[, ...])

Raises NoMemoryError when allocating an instance of the given classes.

[ GitHub ]

# File 'gc.c', line 14215


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

    if (!stress_to_class) {
        set_stress_to_class(rb_ary_hidden_new(argc));
    }
    rb_ary_cat(stress_to_class, argv, argc);
    return self;
}

.compact

This function compacts objects together in Ruby’s heap. It eliminates unused space (or fragmentation) in the heap by moving objects in to that unused space. This function returns a hash which contains statistics about which objects were moved. See .latest_gc_info for details about compaction statistics.

This method is implementation specific and not expected to be implemented in any implementation besides MRI.

To test whether GC compaction is supported, use the idiom:

GC.respond_to?(:compact)

[ GitHub ]

# File 'gc.c', line 11118


static VALUE
gc_compact(VALUE self)
{
    /* Run GC with compaction enabled */
    gc_start_internal(NULL, self, Qtrue, Qtrue, Qtrue, Qtrue);

    return gc_compact_stats(self);
}

.count ⇒ Integer

The number of times GC occurred.

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

[ GitHub ]

# File 'gc.rb', line 105


def self.count
  Primitive.gc_count
end

.disable ⇒ `Boolean`

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

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

[ GitHub ]

# File 'gc.rb', line 69


def self.disable
  Primitive.gc_disable
end

.enable ⇒ `Boolean`

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

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

[ GitHub ]

# File 'gc.rb', line 57


def self.enable
  Primitive.gc_enable
end

.latest_compact_info ⇒ Hash

Returns information about object moved in the most recent GC compaction.

The returned hash has two keys :considered and :moved. The hash for :considered lists the number of objects that were considered for movement by the compactor, and the :moved hash lists the number of objects that were actually moved. Some objects can’t be moved (maybe they were pinned) so these numbers can be used to calculate compaction efficiency.

[ GitHub ]

# File 'gc.c', line 11012


static VALUE
gc_compact_stats(VALUE self)
{
    size_t i;
    rb_objspace_t *objspace = &rb_objspace;
    VALUE h = rb_hash_new();
    VALUE considered = rb_hash_new();
    VALUE moved = rb_hash_new();
    VALUE moved_up = rb_hash_new();
    VALUE moved_down = rb_hash_new();

    for (i=0; i<T_MASK; i++) {
        if (objspace->rcompactor.considered_count_table[i]) {
            rb_hash_aset(considered, type_sym(i), SIZET2NUM(objspace->rcompactor.considered_count_table[i]));
        }

        if (objspace->rcompactor.moved_count_table[i]) {
            rb_hash_aset(moved, type_sym(i), SIZET2NUM(objspace->rcompactor.moved_count_table[i]));
        }

        if (objspace->rcompactor.moved_up_count_table[i]) {
            rb_hash_aset(moved_up, type_sym(i), SIZET2NUM(objspace->rcompactor.moved_up_count_table[i]));
        }

        if (objspace->rcompactor.moved_down_count_table[i]) {
            rb_hash_aset(moved_down, type_sym(i), SIZET2NUM(objspace->rcompactor.moved_down_count_table[i]));
        }
    }

    rb_hash_aset(h, ID2SYM(rb_intern("considered")), considered);
    rb_hash_aset(h, ID2SYM(rb_intern("moved")), moved);
    rb_hash_aset(h, ID2SYM(rb_intern("moved_up")), moved_up);
    rb_hash_aset(h, ID2SYM(rb_intern("moved_down")), moved_down);

    return h;
}

.latest_gc_info ⇒ Hash .latest_gc_info(hash) ⇒ Hash .latest_gc_info(:major_by) ⇒ `:malloc`

Returns information about the most recent garbage collection.

If the optional argument, hash, is given, it is overwritten and returned. This is intended to avoid probe effect.

[ GitHub ]

# File 'gc.rb', line 266


def self.latest_gc_info hash_or_key = nil
  Primitive.gc_latest_gc_info hash_or_key
end

.malloc_allocated_size ⇒ Integer

Returns the size of memory allocated by malloc().

Only available if ruby was built with CALC_EXACT_MALLOC_SIZE.

[ GitHub ]

# File 'gc.c', line 13077


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

.malloc_allocations ⇒ Integer

Returns the number of malloc() allocations.

Only available if ruby was built with CALC_EXACT_MALLOC_SIZE.

[ GitHub ]

# File 'gc.c', line 13092


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

.remove_stress_to_class(class[, ...])

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

[ GitHub ]

# File 'gc.c', line 14235


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) {
            set_stress_to_class(0);
        }
    }
    return Qnil;
}

.start(full_mark: true, immediate_mark: true, immediate_sweep: true)

Initiates garbage collection, even if manually disabled.

The full_mark keyword argument determines whether or not to perform a major garbage collection cycle. When set to true, a major garbage collection cycle is ran, meaning all objects are marked. When set to false, a minor garbage collection cycle is ran, meaning only young objects are marked.

The immediate_mark keyword argument determines whether or not to perform incremental marking. When set to true, marking is completed during the call to this method. When set to false, marking is performed in steps that is interleaved with future Ruby code execution, so marking might not be completed during this method call. Note that if full_mark is false then marking will always be immediate, regardless of the value of immediate_mark.

The immedate_sweep keyword argument determines whether or not to defer sweeping (using lazy sweep). When set to true, sweeping is performed in steps that is interleaved with future Ruby code execution, so sweeping might not be completed during this method call. When set to false, sweeping is completed during the call to this method.

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.

[ GitHub ]

# File 'gc.rb', line 38


def self.start full_mark: true, immediate_mark: true, immediate_sweep: true
  Primitive.gc_start_internal full_mark, immediate_mark, immediate_sweep, false
end

.stat ⇒ Hash .stat(hash) ⇒ Hash .stat(:key) ⇒ Numeric

Returns a ::Hash containing information about the GC.

The contents of the hash are implementation specific and may change in the future without notice.

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

count: The total number of garbage collections ran since application start (count includes both minor and major garbage collections)
time: The total time spent in garbage collections (in milliseconds)
heap_allocated_pages: The total number of :heap_eden_pages + :heap_tomb_pages
heap_sorted_length: The number of pages that can fit into the buffer that holds references to all pages
heap_allocatable_pages: The total number of pages the application could allocate without additional GC
heap_available_slots: The total number of slots in all :heap_allocated_pages
heap_live_slots: The total number of slots which contain live objects
heap_free_slots: The total number of slots which do not contain live objects
heap_final_slots: The total number of slots with pending finalizers to be run
heap_marked_slots: The total number of objects marked in the last GC
heap_eden_pages: The total number of pages which contain at least one live slot
heap_tomb_pages: The total number of pages which do not contain any live slots
total_allocated_pages: The cumulative number of pages allocated since application start
total_freed_pages: The cumulative number of pages freed since application start
total_allocated_objects: The cumulative number of objects allocated since application start
total_freed_objects: The cumulative number of objects freed since application start
malloc_increase_bytes: Amount of memory allocated on the heap for objects. Decreased by any GC
malloc_increase_bytes_limit: When :malloc_increase_bytes crosses this limit, GC is triggered
minor_gc_count: The total number of minor garbage collections run since process start
major_gc_count: The total number of major garbage collections run since process start
compact_count: The total number of compactions run since process start
read_barrier_faults: The total number of times the read barrier was triggered during compaction
total_moved_objects: The total number of objects compaction has moved
remembered_wb_unprotected_objects: The total number of objects without write barriers
remembered_wb_unprotected_objects_limit: When :remembered_wb_unprotected_objects crosses this limit, major GC is triggered
old_objects: Number of live, old objects which have survived at least 3 garbage collections
old_objects_limit: When :old_objects crosses this limit, major GC is triggered
oldmalloc_increase_bytes: Amount of memory allocated on the heap for objects. Decreased by major GC
oldmalloc_increase_bytes_limit: When :old_malloc_increase_bytes crosses this limit, major GC is triggered

If the optional argument, hash, is given, it is overwritten and returned. This is intended to avoid probe effect.

This method is only expected to work on CRuby.

[ GitHub ]

# File 'gc.rb', line 189


def self.stat hash_or_key = nil
  Primitive.gc_stat hash_or_key
end

.stat_heap ⇒ Hash .stat_heap(nil, hash) ⇒ Hash .stat_heap(heap_name) ⇒ Hash .stat_heap(heap_name, hash) ⇒ Hash .stat_heap(heap_name, :key) ⇒ Numeric

Returns information for heaps in the GC.

If the first optional argument, heap_name, is passed in and not nil, it returns a ::Hash containing information about the particular heap. Otherwise, it will return a ::Hash with heap names as keys and a ::Hash containing information about the heap as values.

If the second optional argument, hash_or_key, is given as ::Hash, it will be overwritten and returned. This is intended to avoid the probe effect.

If both optional arguments are passed in and the second optional argument is a symbol, it will return a ::Numeric of the value for the particular heap.

On CRuby, heap_name is of the type ::Integer but may be of type ::String on other implementations.

The contents of the hash are implementation specific and may change in the future without notice.

If the optional argument, hash, is given, it is overwritten and returned.

This method is only expected to work on CRuby.

The hash includes the following keys about the internal information in the GC:

slot_size: The slot size of the heap in bytes.
heap_allocatable_pages: The number of pages that can be allocated without triggering a new garbage collection cycle.
heap_eden_pages: The number of pages in the eden heap.
heap_eden_slots: The total number of slots in all of the pages in the eden heap.
heap_tomb_pages: The number of pages in the tomb heap. The tomb heap only contains pages that do not have any live objects.
heap_tomb_slots: The total number of slots in all of the pages in the tomb heap.
total_allocated_pages: The total number of pages that have been allocated in the heap.
total_freed_pages: The total number of pages that have been freed and released back to the system in the heap.
force_major_gc_count: The number of times major garbage collection cycles this heap has forced to start due to running out of free slots.
force_incremental_marking_finish_count: The number of times this heap has forced incremental marking to complete due to running out of pooled slots.

[ GitHub ]

# File 'gc.rb', line 252


def self.stat_heap heap_name = nil, hash_or_key = nil
  Primitive.gc_stat_heap heap_name, hash_or_key
end

.total_time ⇒ Integer

Return measured GC total time in nano seconds.

[ GitHub ]

# File 'gc.rb', line 318


def self.total_time
  Primitive.cexpr! %{
    ULL2NUM(rb_objspace.profile.marking_time_ns + rb_objspace.profile.sweeping_time_ns)
  }
end

.verify_compaction_references(toward: nil, double_heap: false) ⇒ Hash

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 expands 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.

[ GitHub ]

.verify_internal_consistency ⇒ `nil`

Verify internal consistency.

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

[ GitHub ]

# File 'gc.c', line 8182


static VALUE
gc_verify_internal_consistency_m(VALUE dummy)
{
    gc_verify_internal_consistency(&rb_objspace);
    return Qnil;
}

Instance Method Details

#garbage_collect(full_mark: true, immediate_mark: true, immediate_sweep: true)

Alias of .start

[ GitHub ]

# File 'gc.rb', line 43


def garbage_collect full_mark: true, immediate_mark: true, immediate_sweep: true
  Primitive.gc_start_internal full_mark, immediate_mark, immediate_sweep, false
end

Module: GC

Overview

Constant Summary

Class Attribute Summary

Class Method Summary

Instance Method Summary

Class Attribute Details

.auto_compact ⇒ Boolean (rw)

.auto_compact=(flag) (rw)

.measure_total_time ⇒ Boolean (rw)

.measure_total_time=(true/false) (rw)

.stress ⇒ Boolean (rw)

.stress=(flag) ⇒ flag (rw)

Class Method Details

.add_stress_to_class(class[, ...])

.compact

.count ⇒ Integer

.disable ⇒ Boolean

.enable ⇒ Boolean

.latest_compact_info ⇒ Hash

.latest_gc_info ⇒ Hash .latest_gc_info(hash) ⇒ Hash .latest_gc_info(:major_by) ⇒ :malloc

.malloc_allocated_size ⇒ Integer

.malloc_allocations ⇒ Integer

.remove_stress_to_class(class[, ...])

.start(full_mark: true, immediate_mark: true, immediate_sweep: true)

.stat ⇒ Hash .stat(hash) ⇒ Hash .stat(:key) ⇒ Numeric

.stat_heap ⇒ Hash .stat_heap(nil, hash) ⇒ Hash .stat_heap(heap_name) ⇒ Hash .stat_heap(heap_name, hash) ⇒ Hash .stat_heap(heap_name, :key) ⇒ Numeric

.total_time ⇒ Integer

.verify_compaction_references(toward: nil, double_heap: false) ⇒ Hash

.verify_internal_consistency ⇒ nil

Instance Method Details

#garbage_collect(full_mark: true, immediate_mark: true, immediate_sweep: true)

.auto_compact ⇒ `Boolean` (rw)

.measure_total_time ⇒ `Boolean` (rw)

.stress ⇒ `Boolean` (rw)

.stress=(flag) ⇒ `flag` (rw)

.disable ⇒ `Boolean`

.enable ⇒ `Boolean`

.latest_gc_info ⇒ Hash .latest_gc_info(hash) ⇒ Hash .latest_gc_info(:major_by) ⇒ `:malloc`

.verify_internal_consistency ⇒ `nil`