mirror of https://github.com/dart-lang/sdk synced 2024-09-15 23:29:47 +00:00

Ryan Macnak 6e987b6eb5 [vm, service] Add requestHeapSnapshot.

This replaces _requestHeapSnapshot and _getObjectByAddresses, which relied on the invalid assumption that objects don't move and the heap hasn't mutated since the initial snapshot.

Updates Observatory to the new format. Adds treemap visualization of the dominator tree. Adds the ability to save and load heap snapshots to files. Removes analysis grouping references by source and target class. Removes ability to navigate from a pixel in the fragmentation view to inspector. Removes ability to query the top retaining instance from an ordinary class browser.

Change-Id: Ia7781c05d43bf3ec149f8b4ecab803b37c3ee981
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/112181
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Ben Konyi <bkonyi@google.com>

2019-08-19 19:31:42 +00:00

3.7 KiB

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Dart VM Service Heap Snapshot

A snapshot of a heap in the Dart VM that allows for arbitrary analysis of memory usage.

Object IDs

An object id is a 1-origin index into SnapshotGraph.objects.

Object id 0 is a sentinel value. It indicates target of a reference has been omitted from the snapshot.

The root object is has object id 1.

This notion of id is unrelated to the id used by the rest of the VM service and cannot, for example, be used as a argument to getObject.

Class IDs

A class id is a 1-origin index into SnapshotGraph.classes.

Class id 0 is a sentinel value.

This notion of id is unrelated to the id used by the rest of the VM service and cannot, for example, be used as a argument to getObject.

Graph properties

The graph may contain unreachable objects.

The graph may references without a corresponding SnapshotField.

Format

type SnapshotGraph {
  magic : uint8[8] = "dartheap",

  flags : uleb128,
  name : Utf8String,

  // The sum of shallow sizes of all objects in this graph.
  shallowSize : uleb128,

  // The amount of memory reserved for this heap. At least as large as |shallowSize|.
  capacity : uleb128,

  // The sum of sizes of all external properites in this graph.
  externalSize : uleb128,

  classCount : uleb128,
  classes : SnapshotClass[classCount],

  // At least as big as the sum of SnapshotObject.referenceCount.
  referenceCount : uleb128,
  objectCount : uleb128,
  objects : SnapshotObject[objectCount],

  externalPropertyCount : uleb128,
  externalProperties : SnapshotExternalProperty[externalPropertyCount],
}

type SnapshotClass {
  // Reserved.
  flags : uleb128,

  // The simple (not qualified) name of the class.
  name : Utf8String,

  // The name of the class's library.
  libraryName : Utf8String,

  // The URI of the class's library.
  libraryUri : Utf8String,

  reserved : Utf8String,

  fieldCount : uleb128,
  fields : SnapshotField[fieldCount],
}

type SnapshotField {
  // Reserved.
  flags : uleb128,

  // A 0-origin index into SnapshotObject.references.
  index : uleb128,

  name : Utf8String,

  reserved : Utf8String,
}

type SnapshotObject {
  // A 1-origin index into SnapshotGraph.classes.
  classId : uleb128,

  // The space used by this object in bytes.
  shallowSize : uleb128,

  data : NonReferenceData,

  referenceCount : uleb128,
  // A list of 1-origin indicies into SnapshotGraph.objects
  references : uleb128[referenceCount],
}

type NonReferenceData {
  tag : uleb128,
}

type NoData extends NonReferenceData {
  tag : uleb128 = 0,
}

type NullData extends NonReferenceData {
  tag : uleb128 = 1,
}

type BoolData extends NonReferenceData {
  tag : uleb128 = 2,
  value : uleb128,
}

type IntegerData extends NonReferenceData {
  tag : uleb128 = 3,
  value : uleb128,
}

type DoubleData extends NonReferenceData {
  tag: uleb128 = 4,
  value: float64,
}

type Latin1StringData extends NonReferenceData {
  tag : uleb128 = 5,
  length : uleb128,
  truncatedLength : uleb128,
  codeUnits : uint8[truncatedLength],
}

type Utf16StringData extends NonReferenceData {
  tag : uleb128 = 6,
  length : uleb128,
  truncatedLength : uleb128,
  codeUnits : uint16[truncatedLength],
}

// Indicates the object is variable length, such as a known implementation
// of List, Map or Set.
type LengthData extends NonReferenceData {
  tag : uleb128 = 7,
  length : uleb128,
}

// Indicates the object has some name, such as Function, Field, Class or Library.
type NameData extends NonReferenceData {
  tag : uleb128 = 7,
  name : Utf8String,
}

type SnapshotExternalProperty {
  // A 1-origin index into SnapshotGraph.objects.
  object : uleb128,

  externalSize : uleb128,

  name : Utf8String,
}

type Utf8String {
  length : uleb128,
  codeUnits : uint8[length],
}

3.7 KiB Raw Blame History