module GC

Sets or gets information about the current GC config.

Configuration parameters are GC implementation specific and may change without notice.

This method can be called without parameters to retrieve the current config.

This method can also be called with a Hash argument to assign values to valid config keys. Config keys missing from the passed Hash will be left unmodified.

If a key/value pair is passed to this function that does not correspond to a valid config key for the GC implementation being used, no config will be updated, the key will be present in the returned Hash, and it’s value will be nil. This is to facilitate easy migration between GC implementations.

In both call-seqs the return value of GC.config will be a Hash containing the most recent full configuration. ie. All keys and values defined by the specific GC implementation being used. In the case of a config update, the return value will include the new values being updated.

This method is only expected to work on CRuby.

Valid config keys for Ruby’s default GC implementation are:

rgengc_allow_full_mark

Control whether the GC is allowed to run a full mark (young & old objects).

When true GC interleaves major and minor collections. This is default. GC will function as intended.

When false, the GC will never trigger a full marking cycle unless explicitly requested by user code. Instead only a minor mark will run - only young objects will be marked. When the heap space is exhausted, new pages will be allocated immediately instead of running a full mark.

A flag will be set to notify that a full mark has been requested. This flag is accessible using GC.latest_gc_info(:needs_major_by)

The user can trigger a major collection at any time using GC.start(full_mark: true)

When false. Young to Old object promotion is disabled. For performance reasons it is recommended to warmup an application using Process.warmup before setting this parameter to false.

# File gc.rb, line 306
def self.config hash = nil
  return Primitive.gc_config_get unless hash

  Primitive.gc_config_set hash
end

The number of times GC occurred.

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

# File gc.rb, line 105
def self.count
  Primitive.gc_count
end

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

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

# File gc.rb, line 69
def self.disable
  Primitive.gc_disable
end

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

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

# File gc.rb, line 57
def self.enable
  Primitive.gc_enable
end

Returns information about the most recent garbage collection.

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

If the argument key is given and is a Symbol object, it returns the value associated with the key. This is equivalent to GC.latest_gc_info[key].

# File gc.rb, line 326
def self.latest_gc_info hash_or_key = nil
  if hash_or_key == nil
    hash_or_key = {}
  elsif Primitive.cexpr!("RBOOL(!SYMBOL_P(hash_or_key) && !RB_TYPE_P(hash_or_key, T_HASH))")
    raise TypeError, "non-hash or symbol given"
  end

  Primitive.cstmt! %{
    return rb_gc_latest_gc_info(hash_or_key);
  }
end

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

# File gc.rb, line 356
def self.measure_total_time
  Primitive.cexpr! %{
    RBOOL(rb_gc_impl_get_measure_total_time(rb_gc_get_objspace()))
  }
end

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

# File gc.rb, line 344
def self.measure_total_time=(flag)
  Primitive.cstmt! %{
    rb_gc_impl_set_measure_total_time(rb_gc_get_objspace(), flag);
    return flag;
  }
end

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 immediate_sweep keyword argument determines whether or not to defer sweeping (using lazy sweep). When set to false, 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 true, 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.

# 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

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.

# File gc.rb, line 189
def self.stat hash_or_key = nil
  Primitive.gc_stat hash_or_key
end

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.

# 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

Returns current status of GC stress mode.

# File gc.rb, line 77
def self.stress
  Primitive.gc_stress_get
end

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 95
def self.stress=(flag)
  Primitive.gc_stress_set_m flag
end

Return measured GC total time in nano seconds.

# File gc.rb, line 366
def self.total_time
  Primitive.cexpr! %{
    ULL2NUM(rb_gc_impl_get_total_time(rb_gc_get_objspace()))
  }
end

Alias of GC.start

# 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