dart-lang/sdk
1
0
Fork 0
Code Issues Pull Requests Actions 2 Packages Projects Releases Wiki Activity

master branch to main

Browse Source 
Fixes #47190

TEST=None, only markdown files where edited.

Change-Id: Ife204f9c792b6bce30d0cd7bf2260ced11c8f2b4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/213049
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Alexander Thomas <athom@google.com>
This commit is contained in:
Ahmed Ashour
2021-09-15 06:22:23 +00:00
committed by Alexander Thomas
parent 17503caa05
commit d6975c1905
29 changed files with 60 additions and 60 deletions
Download Patch File Download Diff File Expand all files Collapse all files
runtime/docs/gc.md
+3 -3
View File
@@ -1,6 +1,6 @@
# Garbage Collection
The Dart VM has a generational garbage collector with two generations. The new generation is collected by a parallel, stop-the-world semispace [scavenger](https://github.com/dart-lang/sdk/blob/master/runtime/vm/heap/scavenger.h). The old generation is collected by concurrent-[mark](https://github.com/dart-lang/sdk/blob/master/runtime/vm/heap/marker.h)-concurrent-[sweep](https://github.com/dart-lang/sdk/blob/master/runtime/vm/heap/sweeper.h) or by concurrent-mark-parallel-[compact](https://github.com/dart-lang/sdk/blob/master/runtime/vm/heap/compactor.h).
The Dart VM has a generational garbage collector with two generations. The new generation is collected by a parallel, stop-the-world semispace [scavenger](https://github.com/dart-lang/sdk/blob/main/runtime/vm/heap/scavenger.h). The old generation is collected by concurrent-[mark](https://github.com/dart-lang/sdk/blob/main/runtime/vm/heap/marker.h)-concurrent-[sweep](https://github.com/dart-lang/sdk/blob/main/runtime/vm/heap/sweeper.h) or by concurrent-mark-parallel-[compact](https://github.com/dart-lang/sdk/blob/main/runtime/vm/heap/compactor.h).
## Object representation
@@ -37,7 +37,7 @@ The VM does not know which stack slots, globals or object fields in foreign lang
Any non-GC thread or task that can allocate, read or write to the heap is called a "mutator" (because it can mutate the object graph).
Some phases of GC require that the heap is not being used by a mutator; we call these "[safepoint](https://github.com/dart-lang/sdk/blob/master/runtime/vm/heap/safepoint.h) operations". Examples of safepoint operations include marking roots at the beginning of concurrent marking and the entirety of a scavenge.
Some phases of GC require that the heap is not being used by a mutator; we call these "[safepoint](https://github.com/dart-lang/sdk/blob/main/runtime/vm/heap/safepoint.h) operations". Examples of safepoint operations include marking roots at the beginning of concurrent marking and the entirety of a scavenge.
To perform these operations, all mutators need to temporarily stop accessing the heap; we say that these mutators have reached a "safepoint". A mutator that has reached a safepoint will not resume accessing the heap (leave the safepoint) until the safepoint operation is complete. In addition to not accessing the heap, a mutator at a safepoint must not hold any pointers into the heap unless these pointers can be visited by the GC. For code in the VM runtime, this last property means holding only handles and no ObjectPtr nor UntaggedObject. Examples of places that might enter a safepoint include allocations, stack overflow checks, and transitions between compiled code and the runtime and native code.
@@ -59,7 +59,7 @@ All objects have a bit in their header called the mark bit. At the start of a co
During the marking phase, the collector visits each of the root pointers. If the target object is an old-space object and its mark bit is clear, the mark bit is set and the target added to the marking stack (grey set). The collector then removes and visits objects in the marking stack, marking more old-space objects and adding them to the marking stack, until the marking stack is empty. At this point, all reachable objects have their mark bits set and all unreachable objects have their mark bits clear.
During the sweeping phase, the collector visits each old-space object. If the mark bit is clear, the object's memory is added to a [free list](https://github.com/dart-lang/sdk/blob/master/runtime/vm/heap/freelist.h) to be used for future allocations. Otherwise the object's mark bit is cleared. If every object on some page is unreachable, the page is released to the OS.
During the sweeping phase, the collector visits each old-space object. If the mark bit is clear, the object's memory is added to a [free list](https://github.com/dart-lang/sdk/blob/main/runtime/vm/heap/freelist.h) to be used for future allocations. Otherwise the object's mark bit is cleared. If every object on some page is unreachable, the page is released to the OS.
### New-Space as Roots