11 * [GC](#gc)
60 * Marked for GC or not
73 |               nothing:61          | GC:1 | state:00 |     OOP to metadata object     |       Unlo…
75 |    tId:29    |      Lcount:32     | GC:1 | state:00 |     OOP to metadata object     |  Lightweig…
77 |               Monitor:61          | GC:1 | state:01 |     OOP to metadata object     |  Heavyweig…
79 |                Hash:61            | GC:1 | state:10 |     OOP to metadata object     |       Hash…
81 |           Forwarding address:62          | state:11 |     OOP to metadata object     |         GC…
91 |               nothing:29          | GC:1 | state:00 |     OOP to metadata object     |       Unlo…
93 |    tId:13    |      Lcount:16     | GC:1 | state:00 |     OOP to metadata object     |  Lightweig…
95 |               Monitor:29          | GC:1 | state:01 |     OOP to metadata object     |  Heavyweig…
97 |                Hash:29            | GC:1 | state:10 |     OOP to metadata object     |       Hash…
99 |           Forwarding address:30          | state:11 |     OOP to metadata object     |         GC…
110 |        nothing:28        | Hash:1 | GC:1 | state:00 |     OOP to metadata object     |       Unlo…
112 |  tId:13  |   LCount:15   | Hash:1 | GC:1 | state:00 |     OOP to metadata object     |  Lightweig…
114 |        Monitor:28        | Hash:1 | GC:1 | state:01 |     OOP to metadata object     |  Heavyweig…
116 |   Forwarding address:28  | Hash:1 | GC:1 | state:11 |     OOP to metadata object     |         GC…
120 …t requires extra memory after GC moved the object (where the original hash value will be stored) a…
121 But, this scenario will be useful if we have allocators and GC which decreases such a situation to …
130 |               nothing:13          | GC:1 | state:00 |     OOP to metadata object     |       Unlo…
132 |    thread Id:7    | Lock Count:6  | GC:1 | state:00 |     OOP to metadata object     |  Lightweig…
134 |               Monitor:13          | GC:1 | state:01 |     OOP to metadata object     |  Heavyweig…
136 |                Hash:13            | GC:1 | state:10 |     OOP to metadata object     |       Hash…
138 |         Forwarding address:14            | state:11 |     OOP to metadata object     |         GC…
152 GC - The object has been moved by the GC.
203 | String Hash | GC bit (1 bit) | Status (2 bits) |    <--- Mark Word (32 bits)
302 …e some preallocated buffers which allow Runtime to continue to work, while GC is trying to free me…
316   - Internal memory space for non-compiler part of Runtime (including GC internals)
327 Logical GC spaces:
332 ## GC  section in Memory Management and Object Layout
334 Garbage collector (GC) automatically recycles memory that will never be used again.
336 GC is developped iteratively.
339 - precise GC (see [glossary](./glossary.md#memory-management-terms))
340 - GC should support various [modes](#overview)(performance, power-saving mode, normal mode)
341 - GC suitable for each mode and compliant with this mode (see [here](#overview))
345 - GC barriers supported by Interpreter and JIT
349 So we should have possibility to use a suitable GC for each application.
351 ### Epsilon GC  argument
353 Epsilon GC does absolutely nothing but makes the impression that Runtime has GC. I.e., it supports …
355 Epsilon GC should be used only for debug and profiling purposes. I.e., we can disable GC and measur…
357 ### STW GC  argument
359 Stop-The-World (STW) GC is a non-generational non-moving GC. During its work all mutator threads sh…
365 ### Concurrent Mark Sweep GC  argument
375 - generational moving (optionally compacting) GC
376 - (optional) generational non-moving (optionally compacting) GC
387 Since one of the metric for this GC - high throughput, most objects in the Eden will live long enou…
391 Minor GC (STW):
396 Note: We'll use adaptive thresholds for triggering Minor GC for minimizing the STW pause.
397 Note #2: We can tune Minor GC by trying make concurrent marking and re-mark, but it will require co…
399 Major GC:
409 Note: If we don't have Survivor spaces we can implement non-moving generational GC.
411 ### Region based GC (main)  argument
419 Since the typical heap size for mobile applications is small, this GC can be considered as a good c…
439 Minor GC (only for young regions - STW):
446 Mixed GC - Minor GC + some tenured regions added to the young generation regions after the concurre…
455 ### Low-pause GC (deferred)  argument
462 No explicit Minor GC.
464 Major GC:
471 Note: This GC is suitable for the applications with a big heap or for applications when it is hard …
476 ### GC: interaction with Interpreter, JIT and AOT  argument
496 When GC wants to stop the world, it forces it by stopping all threads at the safepoint.
501 For each safepoint, we should have a method that can provide GC with information about objects on t…
523 #### GC Barriers
525 …GC barrier is a block on writing to (write barrier) or reading from (read barrier) certain memory …
527 ##### GC Write Barriers
529 Heap inconsistency can happen when a GC reclaims alive/reachable objects.
536 So we can solve these issues with GC WRB (write barrier). GC WRB can be _pre_ (inserted before the …
559 ##### GC Read Barriers
568 #### GC Barriers integration with Interpreter and Compiler
581 … could provide some more compiler-friendly interfaces to the other compilers to encode GC barriers.