flutter::DartSnapshot Class Reference

A read-only Dart heap snapshot, or, read-executable mapping of AOT compiled Dart code. More...

#include <dart_snapshot.h>

Inheritance diagram for flutter::DartSnapshot:

Public Member Functions
bool	IsValid () const
	Determines if this snapshot contains a heap component. Since the instructions component is optional, the method does not check for its presence. Use IsValidForAOT to determine if both the heap and instructions components of the snapshot are present.
bool	IsValidForAOT () const
	Determines if this snapshot contains both the heap and instructions components. This is only useful when determining if the snapshot may be used to run AOT code. The instructions component will be absent in JIT modes.
const uint8_t *	GetDataMapping () const
	Get a pointer to the read-only mapping to the heap snapshot.
const uint8_t *	GetInstructionsMapping () const
	Get a pointer to the read-execute mapping to the instructions snapshot.
bool	IsDontNeedSafe () const
	Returns whether both the data and instructions mappings are safe to use with madvise(DONTNEED).
bool	IsNullSafetyEnabled (const fml::Mapping *application_kernel_mapping) const
Public Member Functions inherited from fml::RefCountedThreadSafe< DartSnapshot >
void	Release () const
Public Member Functions inherited from fml::internal::RefCountedThreadSafeBase
void	AddRef () const
bool	HasOneRef () const
void	AssertHasOneRef () const

Static Public Member Functions
static fml::RefPtr< const DartSnapshot >	VMSnapshotFromSettings (const Settings &settings)
	From the fields present in the given settings object, infer the core snapshot.
static fml::RefPtr< const DartSnapshot >	IsolateSnapshotFromSettings (const Settings &settings)
	From the fields present in the given settings object, infer the isolate snapshot.
static fml::RefPtr< DartSnapshot >	IsolateSnapshotFromMappings (const std::shared_ptr< const fml::Mapping > &snapshot_data, const std::shared_ptr< const fml::Mapping > &snapshot_instructions)
	Create an isolate snapshot from existing fml::Mappings.
static fml::RefPtr< DartSnapshot >	VMServiceIsolateSnapshotFromSettings (const Settings &settings)
	Create an isolate snapshot specialized for launching the service isolate. Returns nullptr if no such snapshot is available.

Static Public Attributes
static const char *	kVMDataSymbol = "kDartVmSnapshotData"
static const char *	kVMInstructionsSymbol = "kDartVmSnapshotInstructions"
static const char *	kIsolateDataSymbol = "kDartIsolateSnapshotData"
static const char *	kIsolateInstructionsSymbol

Additional Inherited Members
Protected Member Functions inherited from fml::RefCountedThreadSafe< DartSnapshot >
	RefCountedThreadSafe ()
	~RefCountedThreadSafe ()
Protected Member Functions inherited from fml::internal::RefCountedThreadSafeBase
	RefCountedThreadSafeBase ()
	~RefCountedThreadSafeBase ()
bool	Release () const
void	Adopt ()

Detailed Description

A read-only Dart heap snapshot, or, read-executable mapping of AOT compiled Dart code.

To make Dart code startup more performant, the Flutter tools on the host snapshot the state of the Dart heap at specific points and package the same with the Flutter application. When the Dart VM on the target is configured to run AOT compiled Dart code, the tools also compile the developer's Flutter application code to target specific machine code (instructions). This class deals with the mapping of both these buffers at runtime on the target.

A Flutter application typically needs two instances of this class at runtime to run Dart code. One instance is for the VM and is called the "core snapshot". The other is the isolate and called the "isolate snapshot". Different root isolates can be launched with different isolate snapshots.

These snapshots are typically memory-mapped at runtime, or, referenced directly as symbols present in Mach or ELF binaries.

In the case of the core snapshot, the snapshot is collected when the VM shuts down. The isolate snapshot is collected when the isolate group shuts down.

Definition at line 42 of file dart_snapshot.h.

Member Function Documentation

GetDataMapping()

const uint8_t * flutter::DartSnapshot::GetDataMapping

(

)

const

Get a pointer to the read-only mapping to the heap snapshot.

Returns

The data mapping.

Definition at line 249 of file dart_snapshot.cc.

                                                  {
  return data_ ? data_->GetMapping() : nullptr;
}

GetInstructionsMapping()

const uint8_t * flutter::DartSnapshot::GetInstructionsMapping

(

)

const

Get a pointer to the read-execute mapping to the instructions snapshot.

Returns

The instructions mapping.

Definition at line 253 of file dart_snapshot.cc.

                                                          {
  return instructions_ ? instructions_->GetMapping() : nullptr;
}

IsDontNeedSafe()

bool flutter::DartSnapshot::IsDontNeedSafe

(

)

const

Returns whether both the data and instructions mappings are safe to use with madvise(DONTNEED).

Definition at line 257 of file dart_snapshot.cc.

                                        {
  if (data_ && !data_->IsDontNeedSafe()) {
    return false;
  }
  if (instructions_ && !instructions_->IsDontNeedSafe()) {
    return false;
  }
  return true;
}

IsNullSafetyEnabled()

bool flutter::DartSnapshot::IsNullSafetyEnabled

(

const fml::Mapping *

application_kernel_mapping

)

const

Definition at line 267 of file dart_snapshot.cc.

                                                                     {
  return ::Dart_DetectNullSafety(
      nullptr,           // script_uri (unsupported by Flutter)
      nullptr,           // package_config (package resolution of parent used)
      nullptr,           // original_working_directory (no package config)
      GetDataMapping(),  // snapshot_data
      GetInstructionsMapping(),                 // snapshot_instructions
      kernel ? kernel->GetMapping() : nullptr,  // kernel_buffer
      kernel ? kernel->GetSize() : 0u           // kernel_buffer_size
  );
}

IsolateSnapshotFromMappings()

fml::RefPtr< DartSnapshot > flutter::DartSnapshot::IsolateSnapshotFromMappings ( const std::shared_ptr< const fml::Mapping > &  snapshot_data, const std::shared_ptr< const fml::Mapping > &  snapshot_instructions  )

static

Create an isolate snapshot from existing fml::Mappings.

Parameters

[in]	snapshot_data	The mapping for the heap snapshot.
[in]	snapshot_instructions	The mapping for the instructions snapshot.

Returns

A valid isolate snapshot or nullptr.

Definition at line 205 of file dart_snapshot.cc.

                                                                  {
  auto snapshot =
      fml::MakeRefCounted<DartSnapshot>(snapshot_data, snapshot_instructions);
  if (snapshot->IsValid()) {
    return snapshot;
  }
  return nullptr;
}

IsolateSnapshotFromSettings()

fml::RefPtr< const DartSnapshot > flutter::DartSnapshot::IsolateSnapshotFromSettings ( const Settings &  settings )

static

From the fields present in the given settings object, infer the isolate snapshot.

Attention

Depending on the runtime mode of the Flutter application and the target that Flutter is running on, a complex fallback mechanism is in place to infer the locations of each snapshot buffer. If the caller wants to explicitly specify the buffers of the isolate snapshot, the Settings::isolate_snapshot_data and Settings::isolate_snapshots_instr mapping fields may be used. This specification takes precedence over all fallback search paths.

Parameters

[in]

settings

The settings to infer the isolate snapshot from.

Returns

A valid isolate snapshot or nullptr.

Definition at line 192 of file dart_snapshot.cc.

                              {
  TRACE_EVENT0("flutter", "DartSnapshot::IsolateSnapshotFromSettings");
  auto snapshot =
      fml::MakeRefCounted<DartSnapshot>(ResolveIsolateData(settings),         //
                                        ResolveIsolateInstructions(settings)  //
      );
  if (snapshot->IsValid()) {
    return snapshot;
  }
  return nullptr;
}

IsValid()

bool flutter::DartSnapshot::IsValid

(

)

const

Determines if this snapshot contains a heap component. Since the instructions component is optional, the method does not check for its presence. Use IsValidForAOT to determine if both the heap and instructions components of the snapshot are present.

Returns

Returns if the snapshot contains a heap component.

Definition at line 241 of file dart_snapshot.cc.

                                 {
  return static_cast<bool>(data_);
}

IsValidForAOT()

bool flutter::DartSnapshot::IsValidForAOT

(

)

const

Determines if this snapshot contains both the heap and instructions components. This is only useful when determining if the snapshot may be used to run AOT code. The instructions component will be absent in JIT modes.

Returns

Returns if the snapshot contains both a heap and instructions component.

Definition at line 245 of file dart_snapshot.cc.

                                       {
  return data_ && instructions_;
}

VMServiceIsolateSnapshotFromSettings()

fml::RefPtr< DartSnapshot > flutter::DartSnapshot::VMServiceIsolateSnapshotFromSettings ( const Settings &  settings )

static

Create an isolate snapshot specialized for launching the service isolate. Returns nullptr if no such snapshot is available.

Returns

A valid isolate snapshot or nullptr.

Definition at line 216 of file dart_snapshot.cc.

                              {
#if DART_SNAPSHOT_STATIC_LINK
  return nullptr;
#else   // DART_SNAPSHOT_STATIC_LINK
  if (settings.vmservice_snapshot_library_path.empty()) {
    return nullptr;
  }
 
  std::shared_ptr<const fml::Mapping> snapshot_data =
      SearchMapping(nullptr, "", settings.vmservice_snapshot_library_path,
                    DartSnapshot::kIsolateDataSymbol, false);
  std::shared_ptr<const fml::Mapping> snapshot_instructions =
      SearchMapping(nullptr, "", settings.vmservice_snapshot_library_path,
                    DartSnapshot::kIsolateInstructionsSymbol, true);
  return IsolateSnapshotFromMappings(snapshot_data, snapshot_instructions);
#endif  // DART_SNAPSHOT_STATIC_LINK
}

VMSnapshotFromSettings()

fml::RefPtr< const DartSnapshot > flutter::DartSnapshot::VMSnapshotFromSettings ( const Settings &  settings )

static

From the fields present in the given settings object, infer the core snapshot.

Attention

Depending on the runtime mode of the Flutter application and the target that Flutter is running on, a complex fallback mechanism is in place to infer the locations of each snapshot buffer. If the caller wants to explicitly specify the buffers of the core snapshot, the Settings::vm_snapshot_data and Settings::vm_snapshots_instr mapping fields may be used. This specification takes precedence over all fallback search paths.

Parameters

[in]

settings

The settings to infer the core snapshot from.

Returns

A valid core snapshot or nullptr.

Definition at line 179 of file dart_snapshot.cc.

                              {
  TRACE_EVENT0("flutter", "DartSnapshot::VMSnapshotFromSettings");
  auto snapshot =
      fml::MakeRefCounted<DartSnapshot>(ResolveVMData(settings),         //
                                        ResolveVMInstructions(settings)  //
      );
  if (snapshot->IsValid()) {
    return snapshot;
  }
  return nullptr;
}

Member Data Documentation

kIsolateDataSymbol

const char * flutter::DartSnapshot::kIsolateDataSymbol = "kDartIsolateSnapshotData"

static

The symbol name of the heap data of the isolate snapshot in a dynamic library or currently loaded process.

Definition at line 58 of file dart_snapshot.h.

kIsolateInstructionsSymbol

const char * flutter::DartSnapshot::kIsolateInstructionsSymbol

static

Initial value:

=
    "kDartIsolateSnapshotInstructions"

The symbol name of the instructions data of the isolate snapshot in a dynamic library or currently loaded process.

Definition at line 63 of file dart_snapshot.h.

kVMDataSymbol

const char * flutter::DartSnapshot::kVMDataSymbol = "kDartVmSnapshotData"

static

The symbol name of the heap data of the core snapshot in a dynamic library or currently loaded process.

Definition at line 48 of file dart_snapshot.h.

kVMInstructionsSymbol

const char * flutter::DartSnapshot::kVMInstructionsSymbol = "kDartVmSnapshotInstructions"

static

The symbol name of the instructions data of the core snapshot in a dynamic library or currently loaded process.

Definition at line 53 of file dart_snapshot.h.

---

The documentation for this class was generated from the following files:

• runtime/dart_snapshot.h
• runtime/dart_snapshot.cc