state-enter

Since 4.4

The state-enter command works in conjunction with state-leave to facilitate advanced settling in subscriptions.

state-enter causes a watch to be marked as being in a particular named state. The state is asserted until a corresponding state-leave command is issued or until the watchman client session that entered the state disconnects. This automatic cleanup helps to avoid breaking subscribers if the tooling that initiated a state terminates unexpectedly.

Subscriptions can use the defer and drop fields to defer or drop notifications generated while the watch is in a particular named state.

Examples

This is the simplest example; entering a state named mystate:

["state-enter", "/path/to/root", "mystate"]

It will cause any subscribers to receive a unilateral subscription PDU from the watchman server:

{
  "subscription":  "mysubscriptionname",
  "root":          "/path/to/root",
  "state-enter":   "mystate",
  "clock":         "c:1446410081:18462:7:127"
}

The clock field in the response is the (synchronized; see below) clock at the time that the state was entered and can be used in subsequent queries, in combination with the corresponding state-leave subscription PDU clock, to locate things that changed while the state was asserted.

A more complex example demonstrates passing metadata to any subscribers. The metadata field is propagated through to the subscribers and is not interpreted by the watchman server. It can be any JSON value.

["state-enter", "/path/to/root", {
  "name": "mystate",
  "metadata": {
    "foo": "bar"
  }
}]

This will emit the following unilateral subscription PDU to all subscribers:

{
  "subscription":  "mysubscriptionname",
  "root":          "/path/to/root",
  "state-enter":   "mystate",
  "clock":         "c:1446410081:18462:7:137",
  "metadata": {
    "foo": "bar"
  }
}

Synchronization

States are synchronized with the state of the filesystem so that it is possible for subscribers to reason about when files changed with respect to the state.

This means that issuing a state-enter command will perform query synchronization to ensure that things are in sync.

The state-enter command will use a default sync_timeout of 60 seconds. If the synchronization cookie is not observed within the configured sync_timeout, an error will be returned and the state will not be entered.

In some cases, perhaps during the initial crawl of a very large tree, You may specify an alternative value for the timeout; the value is expressed in milliseconds:

["state-enter", "/path/to/root", {
  "name": "mystate",
  "sync_timeout": 10000,
  "metadata": {
    "foo": "bar"
  }
}]

You may also specify 0 for the timeout to disable synchronization for this particular command. This may cause the state to appear to clients to have been entered logically before it actually did in the case that there are buffered notifications that have not yet been processed by watchman at the time that the state was entered.