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Node.js v14.0.0-nightly201911012d8307e199 Documentation
Table of Contents
-
- v8.cachedDataVersionTag()
- v8.getHeapSpaceStatistics()
- v8.getHeapSnapshot()
- v8.getHeapStatistics()
- v8.getHeapCodeStatistics()
- v8.setFlagsFromString(flags)
- v8.writeHeapSnapshot([filename])
-
- v8.serialize(value)
- v8.deserialize(buffer)
-
- new Serializer()
- serializer.writeHeader()
- serializer.writeValue(value)
- serializer.releaseBuffer()
- serializer.transferArrayBuffer(id, arrayBuffer)
- serializer.writeUint32(value)
- serializer.writeUint64(hi, lo)
- serializer.writeDouble(value)
- serializer.writeRawBytes(buffer)
- serializer._writeHostObject(object)
- serializer._getDataCloneError(message)
- serializer._getSharedArrayBufferId(sharedArrayBuffer)
- serializer._setTreatArrayBufferViewsAsHostObjects(flag)
-
- new Deserializer(buffer)
- deserializer.readHeader()
- deserializer.readValue()
- deserializer.transferArrayBuffer(id, arrayBuffer)
- deserializer.getWireFormatVersion()
- deserializer.readUint32()
- deserializer.readUint64()
- deserializer.readDouble()
- deserializer.readRawBytes(length)
- deserializer._readHostObject()
- class: v8.DefaultSerializer
- class: v8.DefaultDeserializer
V8#
The v8
module exposes APIs that are specific to the version of V8
built into the Node.js binary. It can be accessed using:
const v8 = require('v8');
The APIs and implementation are subject to change at any time.
v8.cachedDataVersionTag()#
- Returns: <integer>
Returns an integer representing a "version tag" derived from the V8 version,
command line flags and detected CPU features. This is useful for determining
whether a vm.Script
cachedData
buffer is compatible with this instance
of V8.
v8.getHeapSpaceStatistics()[src]#
- Returns: <Object[]>
Returns statistics about the V8 heap spaces, i.e. the segments which make up
the V8 heap. Neither the ordering of heap spaces, nor the availability of a
heap space can be guaranteed as the statistics are provided via the V8
GetHeapSpaceStatistics
function and may change from one V8 version to the
next.
The value returned is an array of objects containing the following properties:
space_name
<string>space_size
<number>space_used_size
<number>space_available_size
<number>physical_space_size
<number>
[
{
"space_name": "new_space",
"space_size": 2063872,
"space_used_size": 951112,
"space_available_size": 80824,
"physical_space_size": 2063872
},
{
"space_name": "old_space",
"space_size": 3090560,
"space_used_size": 2493792,
"space_available_size": 0,
"physical_space_size": 3090560
},
{
"space_name": "code_space",
"space_size": 1260160,
"space_used_size": 644256,
"space_available_size": 960,
"physical_space_size": 1260160
},
{
"space_name": "map_space",
"space_size": 1094160,
"space_used_size": 201608,
"space_available_size": 0,
"physical_space_size": 1094160
},
{
"space_name": "large_object_space",
"space_size": 0,
"space_used_size": 0,
"space_available_size": 1490980608,
"physical_space_size": 0
}
]
v8.getHeapSnapshot()[src]#
- Returns: <stream.Readable> A Readable Stream containing the V8 heap snapshot
Generates a snapshot of the current V8 heap and returns a Readable Stream that may be used to read the JSON serialized representation. This JSON stream format is intended to be used with tools such as Chrome DevTools. The JSON schema is undocumented and specific to the V8 engine, and may change from one version of V8 to the next.
const stream = v8.getHeapSnapshot();
stream.pipe(process.stdout);
v8.getHeapStatistics()[src]#
- Returns: <Object>
Returns an object with the following properties:
total_heap_size
<number>total_heap_size_executable
<number>total_physical_size
<number>total_available_size
<number>used_heap_size
<number>heap_size_limit
<number>malloced_memory
<number>peak_malloced_memory
<number>does_zap_garbage
<number>number_of_native_contexts
<number>number_of_detached_contexts
<number>
does_zap_garbage
is a 0/1 boolean, which signifies whether the
--zap_code_space
option is enabled or not. This makes V8 overwrite heap
garbage with a bit pattern. The RSS footprint (resident memory set) gets bigger
because it continuously touches all heap pages and that makes them less likely
to get swapped out by the operating system.
number_of_native_contexts
The value of native_context is the number of the
top-level contexts currently active. Increase of this number over time indicates
a memory leak.
number_of_detached_contexts
The value of detached_context is the number
of contexts that were detached and not yet garbage collected. This number
being non-zero indicates a potential memory leak.
{
total_heap_size: 7326976,
total_heap_size_executable: 4194304,
total_physical_size: 7326976,
total_available_size: 1152656,
used_heap_size: 3476208,
heap_size_limit: 1535115264,
malloced_memory: 16384,
peak_malloced_memory: 1127496,
does_zap_garbage: 0,
number_of_native_contexts: 1,
number_of_detached_contexts: 0
}
v8.getHeapCodeStatistics()[src]#
- Returns: <Object>
Returns an object with the following properties:
code_and_metadata_size
<number>bytecode_and_metadata_size
<number>external_script_source_size
<number>
{
code_and_metadata_size: 212208,
bytecode_and_metadata_size: 161368,
external_script_source_size: 1410794
}
v8.setFlagsFromString(flags)[src]#
flags
<string>
The v8.setFlagsFromString()
method can be used to programmatically set
V8 command line flags. This method should be used with care. Changing settings
after the VM has started may result in unpredictable behavior, including
crashes and data loss; or it may simply do nothing.
The V8 options available for a version of Node.js may be determined by running
node --v8-options
.
Usage:
// Print GC events to stdout for one minute.
const v8 = require('v8');
v8.setFlagsFromString('--trace_gc');
setTimeout(() => { v8.setFlagsFromString('--notrace_gc'); }, 60e3);
v8.writeHeapSnapshot([filename])[src]#
filename
<string> The file path where the V8 heap snapshot is to be saved. If not specified, a file name with the pattern'Heap-${yyyymmdd}-${hhmmss}-${pid}-${thread_id}.heapsnapshot'
will be generated, where{pid}
will be the PID of the Node.js process,{thread_id}
will be0
whenwriteHeapSnapshot()
is called from the main Node.js thread or the id of a worker thread.- Returns: <string> The filename where the snapshot was saved.
Generates a snapshot of the current V8 heap and writes it to a JSON file. This file is intended to be used with tools such as Chrome DevTools. The JSON schema is undocumented and specific to the V8 engine, and may change from one version of V8 to the next.
A heap snapshot is specific to a single V8 isolate. When using Worker Threads, a heap snapshot generated from the main thread will not contain any information about the workers, and vice versa.
const { writeHeapSnapshot } = require('v8');
const {
Worker,
isMainThread,
parentPort
} = require('worker_threads');
if (isMainThread) {
const worker = new Worker(__filename);
worker.once('message', (filename) => {
console.log(`worker heapdump: ${filename}`);
// Now get a heapdump for the main thread.
console.log(`main thread heapdump: ${writeHeapSnapshot()}`);
});
// Tell the worker to create a heapdump.
worker.postMessage('heapdump');
} else {
parentPort.once('message', (message) => {
if (message === 'heapdump') {
// Generate a heapdump for the worker
// and return the filename to the parent.
parentPort.postMessage(writeHeapSnapshot());
}
});
}
Serialization API#
The serialization API provides means of serializing JavaScript values in a way that is compatible with the HTML structured clone algorithm. The format is backward-compatible (i.e. safe to store to disk).
This API is under development, and changes (including incompatible changes to the API or wire format) may occur until this warning is removed.
v8.serialize(value)[src]#
Uses a DefaultSerializer
to serialize value
into a buffer.
v8.deserialize(buffer)[src]#
buffer
<Buffer> | <TypedArray> | <DataView> A buffer returned byserialize()
.
Uses a DefaultDeserializer
with default options to read a JS value
from a buffer.
class: v8.Serializer#
new Serializer()#
Creates a new Serializer
object.
serializer.writeHeader()#
Writes out a header, which includes the serialization format version.
serializer.writeValue(value)#
value
<any>
Serializes a JavaScript value and adds the serialized representation to the internal buffer.
This throws an error if value
cannot be serialized.
serializer.releaseBuffer()#
- Returns: <Buffer>
Returns the stored internal buffer. This serializer should not be used once the buffer is released. Calling this method results in undefined behavior if a previous write has failed.
serializer.transferArrayBuffer(id, arrayBuffer)#
id
<integer> A 32-bit unsigned integer.arrayBuffer
<ArrayBuffer> AnArrayBuffer
instance.
Marks an ArrayBuffer
as having its contents transferred out of band.
Pass the corresponding ArrayBuffer
in the deserializing context to
deserializer.transferArrayBuffer()
.
serializer.writeUint32(value)#
value
<integer>
Write a raw 32-bit unsigned integer.
For use inside of a custom serializer._writeHostObject()
.
serializer.writeUint64(hi, lo)#
Write a raw 64-bit unsigned integer, split into high and low 32-bit parts.
For use inside of a custom serializer._writeHostObject()
.
serializer.writeDouble(value)#
value
<number>
Write a JS number
value.
For use inside of a custom serializer._writeHostObject()
.
serializer.writeRawBytes(buffer)#
buffer
<Buffer> | <TypedArray> | <DataView>
Write raw bytes into the serializer’s internal buffer. The deserializer
will require a way to compute the length of the buffer.
For use inside of a custom serializer._writeHostObject()
.
serializer._writeHostObject(object)#
object
<Object>
This method is called to write some kind of host object, i.e. an object created
by native C++ bindings. If it is not possible to serialize object
, a suitable
exception should be thrown.
This method is not present on the Serializer
class itself but can be provided
by subclasses.
serializer._getDataCloneError(message)#
message
<string>
This method is called to generate error objects that will be thrown when an object can not be cloned.
This method defaults to the Error
constructor and can be overridden on
subclasses.
serializer._getSharedArrayBufferId(sharedArrayBuffer)#
sharedArrayBuffer
<SharedArrayBuffer>
This method is called when the serializer is going to serialize a
SharedArrayBuffer
object. It must return an unsigned 32-bit integer ID for
the object, using the same ID if this SharedArrayBuffer
has already been
serialized. When deserializing, this ID will be passed to
deserializer.transferArrayBuffer()
.
If the object cannot be serialized, an exception should be thrown.
This method is not present on the Serializer
class itself but can be provided
by subclasses.
serializer._setTreatArrayBufferViewsAsHostObjects(flag)#
flag
<boolean> Default:false
Indicate whether to treat TypedArray
and DataView
objects as
host objects, i.e. pass them to serializer._writeHostObject()
.
class: v8.Deserializer#
new Deserializer(buffer)#
buffer
<Buffer> | <TypedArray> | <DataView> A buffer returned byserializer.releaseBuffer()
.
Creates a new Deserializer
object.
deserializer.readHeader()#
Reads and validates a header (including the format version).
May, for example, reject an invalid or unsupported wire format. In that case,
an Error
is thrown.
deserializer.readValue()#
Deserializes a JavaScript value from the buffer and returns it.
deserializer.transferArrayBuffer(id, arrayBuffer)#
id
<integer> A 32-bit unsigned integer.arrayBuffer
<ArrayBuffer> | <SharedArrayBuffer> AnArrayBuffer
instance.
Marks an ArrayBuffer
as having its contents transferred out of band.
Pass the corresponding ArrayBuffer
in the serializing context to
serializer.transferArrayBuffer()
(or return the id
from
serializer._getSharedArrayBufferId()
in the case of SharedArrayBuffer
s).
deserializer.getWireFormatVersion()#
- Returns: <integer>
Reads the underlying wire format version. Likely mostly to be useful to
legacy code reading old wire format versions. May not be called before
.readHeader()
.
deserializer.readUint32()#
- Returns: <integer>
Read a raw 32-bit unsigned integer and return it.
For use inside of a custom deserializer._readHostObject()
.
deserializer.readUint64()#
- Returns: <integer[]>
Read a raw 64-bit unsigned integer and return it as an array [hi, lo]
with two 32-bit unsigned integer entries.
For use inside of a custom deserializer._readHostObject()
.
deserializer.readDouble()#
- Returns: <number>
Read a JS number
value.
For use inside of a custom deserializer._readHostObject()
.
deserializer.readRawBytes(length)[src]#
Read raw bytes from the deserializer’s internal buffer. The length
parameter
must correspond to the length of the buffer that was passed to
serializer.writeRawBytes()
.
For use inside of a custom deserializer._readHostObject()
.
deserializer._readHostObject()#
This method is called to read some kind of host object, i.e. an object that is created by native C++ bindings. If it is not possible to deserialize the data, a suitable exception should be thrown.
This method is not present on the Deserializer
class itself but can be
provided by subclasses.
class: v8.DefaultSerializer#
A subclass of Serializer
that serializes TypedArray
(in particular Buffer
) and DataView
objects as host objects, and only
stores the part of their underlying ArrayBuffer
s that they are referring to.
class: v8.DefaultDeserializer#
A subclass of Deserializer
corresponding to the format written by
DefaultSerializer
.