worker: initial implementation

Implement multi-threading support for most of the API.

Thanks to Stephen Belanger for reviewing this change in its
original form, to Olivia Hugger for reviewing the
documentation and some of the tests coming along with it,
and to Alexey Orlenko and Timothy Gu for reviewing other
parts of the tests.

Refs: ayojs/ayo#110
Refs: ayojs/ayo#114
Refs: ayojs/ayo#117

doc/api/errors.md

@@ -1313,6 +1313,13 @@ but not provided in the `transferList` for that call.
 
 An [ES6 module][] could not be resolved.
 
+<a id="ERR_MISSING_PLATFORM_FOR_WORKER"></a>
+### ERR_MISSING_PLATFORM_FOR_WORKER
+
+The V8 platform used by this instance of Node does not support creating Workers.
+This is caused by lack of embedder support for Workers. In particular, this
+error will not occur with standard builds of Node.js.
+
 <a id="ERR_MODULE_RESOLUTION_LEGACY"></a>
 ### ERR_MODULE_RESOLUTION_LEGACY
 
@@ -1722,6 +1729,35 @@ The fulfilled value of a linking promise is not a `vm.Module` object.
 The current module's status does not allow for this operation. The specific
 meaning of the error depends on the specific function.
 
+<a id="ERR_WORKER_DOMAIN"></a>
+### ERR_WORKER_DOMAIN
+
+Used when trying to access the `domain` module inside of a worker thread.
+
+<a id="ERR_WORKER_NEED_ABSOLUTE_PATH"></a>
+### ERR_WORKER_NEED_ABSOLUTE_PATH
+
+Used when the path for the main script of a worker is not an absolute path.
+
+<a id="ERR_WORKER_OUT_OF_MEMORY"></a>
+### ERR_WORKER_OUT_OF_MEMORY
+
+Used when a worker hits its memory limit.
+
+<a id="ERR_WORKER_UNAVAILABLE_FEATURE"></a>
+### ERR_WORKER_UNAVAILABLE_FEATURE
+
+<a id="ERR_WORKER_UNSERIALIZABLE_ERROR"></a>
+### ERR_WORKER_UNSERIALIZABLE_ERROR
+
+Used when all attempts at serializing an uncaught exception from a worker fail.
+
+<a id="ERR_WORKER_UNSUPPORTED_EXTENSION"></a>
+### ERR_WORKER_UNSUPPORTED_EXTENSION
+
+Used when the pathname used for the main script of a worker has an
+unknown file extension.
+
 <a id="ERR_ZLIB_INITIALIZATION_FAILED"></a>
 ### ERR_ZLIB_INITIALIZATION_FAILED
 

doc/api/process.md

@@ -410,6 +410,8 @@ added: v0.7.0
 The `process.abort()` method causes the Node.js process to exit immediately and
 generate a core file.
 
+This feature is not available in [`Worker`][] threads.
+
 ## process.arch
 <!-- YAML
 added: v0.5.0
@@ -517,6 +519,8 @@ try {
 }
 ```
 
+This feature is not available in [`Worker`][] threads.
+
 ## process.config
 <!-- YAML
 added: v0.7.7
@@ -918,6 +922,8 @@ console.log(process.env.test);
 // => 1
 ```
 
+*Note*: `process.env` is read-only in [`Worker`][] threads.
+
 ## process.execArgv
 <!-- YAML
 added: v0.7.7
@@ -1030,6 +1036,9 @@ If it is necessary to terminate the Node.js process due to an error condition,
 throwing an *uncaught* error and allowing the process to terminate accordingly
 is safer than calling `process.exit()`.
 
+*Note*: in [`Worker`][] threads, this function stops the current thread rather
+than the current process.
+
 ## process.exitCode
 <!-- YAML
 added: v0.11.8
@@ -1204,6 +1213,8 @@ console.log(process.getgroups());         // [ 27, 30, 46, 1000 ]
 This function is only available on POSIX platforms (i.e. not Windows or
 Android).
 
+This feature is not available in [`Worker`][] threads.
+
 ## process.kill(pid[, signal])
 <!-- YAML
 added: v0.0.6
@@ -1570,6 +1581,8 @@ if (process.getegid && process.setegid) {
 This function is only available on POSIX platforms (i.e. not Windows or
 Android).
 
+This feature is not available in [`Worker`][] threads.
+
 ## process.seteuid(id)
 <!-- YAML
 added: v2.0.0
@@ -1597,6 +1610,8 @@ if (process.geteuid && process.seteuid) {
 This function is only available on POSIX platforms (i.e. not Windows or
 Android).
 
+This feature is not available in [`Worker`][] threads.
+
 ## process.setgid(id)
 <!-- YAML
 added: v0.1.31
@@ -1624,6 +1639,8 @@ if (process.getgid && process.setgid) {
 This function is only available on POSIX platforms (i.e. not Windows or
 Android).
 
+This feature is not available in [`Worker`][] threads.
+
 ## process.setgroups(groups)
 <!-- YAML
 added: v0.9.4
@@ -1640,6 +1657,8 @@ The `groups` array can contain numeric group IDs, group names or both.
 This function is only available on POSIX platforms (i.e. not Windows or
 Android).
 
+This feature is not available in [`Worker`][] threads.
+
 ## process.setuid(id)
 <!-- YAML
 added: v0.1.28
@@ -1664,6 +1683,7 @@ if (process.getuid && process.setuid) {
 
 This function is only available on POSIX platforms (i.e. not Windows or
 Android).
+This feature is not available in [`Worker`][] threads.
 
 ## process.setUncaughtExceptionCaptureCallback(fn)
 <!-- YAML
@@ -1700,6 +1720,8 @@ a [Writable][] stream.
 `process.stderr` differs from other Node.js streams in important ways, see
 [note on process I/O][] for more information.
 
+This feature is not available in [`Worker`][] threads.
+
 ## process.stdin
 
 * {Stream}
@@ -1732,6 +1754,8 @@ In "old" streams mode the `stdin` stream is paused by default, so one
 must call `process.stdin.resume()` to read from it. Note also that calling
 `process.stdin.resume()` itself would switch stream to "old" mode.
 
+This feature is not available in [`Worker`][] threads.
+
 ## process.stdout
 
 * {Stream}
@@ -1750,6 +1774,8 @@ process.stdin.pipe(process.stdout);
 `process.stdout` differs from other Node.js streams in important ways, see
 [note on process I/O][] for more information.
 
+This feature is not available in [`Worker`][] threads.
+
 ### A note on process I/O
 
 `process.stdout` and `process.stderr` differ from other Node.js streams in
@@ -1865,6 +1891,8 @@ console.log(
 );
 ```
 
+This feature is not available in [`Worker`][] threads.
+
 ## process.uptime()
 <!-- YAML
 added: v0.5.0
@@ -2011,6 +2039,7 @@ cases:
 [`require.resolve()`]: modules.html#modules_require_resolve_request_options
 [`setTimeout(fn, 0)`]: timers.html#timers_settimeout_callback_delay_args
 [`v8.setFlagsFromString()`]: v8.html#v8_v8_setflagsfromstring_flags
+[`Worker`]: worker.html#worker_worker
 [Android building]: https://github.com/nodejs/node/blob/master/BUILDING.md#androidandroid-based-devices-eg-firefox-os
 [Child Process]: child_process.html
 [Cluster]: cluster.html