SturdyRef

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(consistent categorization)
(describe getRcvr in general; clarify broken results; clarify differences between /0 and /2)
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== Protocol ==
== Protocol ==
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{{instance msgdoc|getRcvr|0||any}}
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===getRcvr (both /0 and /2) ===
Returns a promise for a [[live ref]] to the referent of this SturdyRef.
Returns a promise for a [[live ref]] to the referent of this SturdyRef.
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If this vat cannot ''currently'' connect to the host vat, then the result will resolve to a [[broken ref]]; however, a broken ref can also be what the host vat returns as the referent. (XXX do we want to provide for distinguishing these cases?)
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The promise can break if:
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* A connection attempt fails (for /0), or the timeout is reached (for /2).
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* The referent is a broken ref.
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* The host vat no longer has this object registered for lookup by this SturdyRef (no longer has an entry for this SturdyRef's [[SwissNumber]]).
This operation can only be done while the local comm system is [[Introducer#onTheAir/0|on the air]]; otherwise it throws XXX specify exception.
This operation can only be done while the local comm system is [[Introducer#onTheAir/0|on the air]]; otherwise it throws XXX specify exception.
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{{instance msgdoc|getRcvr|2|<var>pollMillis</var> :([[int]] > 0), <var>timeout</var> :([[int]] >&#x3d; -1)|any}}
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{{instance msgdoc|getRcvr|0||any}}
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(XXX this text is copied with changes from the old JavaDoc; see notes)
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If there is not already a connection to the host vat, and this vat cannot ''currently'' connect to the host vat, resolves to a broken ref.
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Like getRcvr() but doesn't resolve the result until we connect to the object's hosting vat. (XXX what is the observable distinction of "doesn't resolve...until..."? What does getRcvr/0 do differently?)
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{{instance msgdoc|getRcvr|2|<var>pollMillis</var> :([[int]] > 0), <var>timeout</var> :([[int]] >&#x3d; -1)|any}}
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Note that the result may still resolve to broken, if the object's hosting vat, for example, no longer has this object registered for lookup by this SturdyRef (no longer has an entry for this SturdyRef's [[SwissNumber]]). (XXX isn't this true for both?)
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This operation can only be done while the local comm system is [[Introducer#onTheAir/0|on the air]]; otherwise it throws XXX specify exception.
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Continuously attempts to connect; doesn't fail unless the absolute time <var>timeout</var> is reached.
<var>pollMillis</var> is a polling interval hint. (XXX the following is an implementation description; rewrite as spec) Until we have [[VLS rendezvous]] support, the best we can do is poll the attempt to connect to the hosting vat. <var>pollMillis</var> says how often we should do so, and thereby tradeoff CPU/comm against promptness. Once we have VLS rendezvous support, then we will post a long-lived query with the relevant [[VLS]]es, and refresh this query at a frequency determined by those [[VLS]]es, not by our client. This refreshing is also a polling loop, but can be long without impeding the responsiveness of getting connected.
<var>pollMillis</var> is a polling interval hint. (XXX the following is an implementation description; rewrite as spec) Until we have [[VLS rendezvous]] support, the best we can do is poll the attempt to connect to the hosting vat. <var>pollMillis</var> says how often we should do so, and thereby tradeoff CPU/comm against promptness. Once we have VLS rendezvous support, then we will post a long-lived query with the relevant [[VLS]]es, and refresh this query at a frequency determined by those [[VLS]]es, not by our client. This refreshing is also a polling loop, but can be long without impeding the responsiveness of getting connected.
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<var>timeout</var> is the time in absMillis (since the [[epoch]]) at which we should give up trying to connect. Once the time has passed, we should resolve the result to broken rather than continuing to poll or refresh. A value of -1 means to keep trying forever.
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<var>timeout</var> is the time in [[absMillis]] at which we should give up trying to connect. Once the time has passed, we should resolve the result to broken rather than continuing to poll or refresh. A value of -1 means to keep trying forever.
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This operation can only be done while the local comm system is [[Introducer#onTheAir/0|on the air]]; otherwise it throws XXX specify exception.
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== Implementation ==
== Implementation ==

Revision as of 17:18, 11 October 2008

For more context see [1] (XXX to be integrated)

A SturdyRef is a reference to an object in another vat (henceforth called the host vat) which does not break on network failure or vat incarnation death as live refs do.

The SturdyRef itself is a near ref, an ordinary local object. SturdyRefs are Selfless but not Transparent.

A SturdyRef refers to something in the host vat by a swiss number; the host vat may at any time change or forget the number/referent association.

SturdyRefs map one-to-one to CapTP URLs; the conversion is provided by <captp>.

Contents

Protocol

getRcvr (both /0 and /2)

Returns a promise for a live ref to the referent of this SturdyRef.

The promise can break if:

  • A connection attempt fails (for /0), or the timeout is reached (for /2).
  • The referent is a broken ref.
  • The host vat no longer has this object registered for lookup by this SturdyRef (no longer has an entry for this SturdyRef's SwissNumber).

This operation can only be done while the local comm system is on the air; otherwise it throws XXX specify exception.

getRcvr/0

Signature: getRcvr() :any

If there is not already a connection to the host vat, and this vat cannot currently connect to the host vat, resolves to a broken ref.

getRcvr/2

Signature: getRcvr(pollMillis :(int > 0), timeout :(int >= -1)) :any

Continuously attempts to connect; doesn't fail unless the absolute time timeout is reached.

pollMillis is a polling interval hint. (XXX the following is an implementation description; rewrite as spec) Until we have VLS rendezvous support, the best we can do is poll the attempt to connect to the hosting vat. pollMillis says how often we should do so, and thereby tradeoff CPU/comm against promptness. Once we have VLS rendezvous support, then we will post a long-lived query with the relevant VLSes, and refresh this query at a frequency determined by those VLSes, not by our client. This refreshing is also a polling loop, but can be long without impeding the responsiveness of getting connected.

timeout is the time in absMillis at which we should give up trying to connect. Once the time has passed, we should resolve the result to broken rather than continuing to poll or refresh. A value of -1 means to keep trying forever.

Implementation

A SturdyRef needs to store the same components as a CapTP URL (search path, host VatID, and swiss number), plus the LocatorUnum so that it can get the live ref to return.

This page is a stub; it should be expanded with more information. If doing so, check the original E web site and the mailing list archives for content which could be moved into this page.
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