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video6.html
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<!-- THIS FILE BEGAN AS A COPY OF video/video4.html.
It has been transformed into the true html file for the twophase video.
-->
<!DOCTYPE html>
<html>
<head>
<!--************************************************************************
* The following imported JavaScript code is involved in copying text into *
* the copy buffer and was obtained from *
* *
* https://clipboardjs.com/ *
* *
* Note that the directory /dist that contains the clipboard.min.js file *
* must be moved to the right place and the src address corrected. *
*************************************************************************-->
<script src="dist/clipboard.min.js">
</script>
<script>
/***************************************************************************
* DATA FOR THE LECTURE *
* *
* The following data customizes the page for a particular video. *
***************************************************************************/
/***************************************************************************
* The name of the lecture. *
***************************************************************************/
var HEADING = "Two-Phase Commit" ;
/***************************************************************************
* Table of Contents *
* *
* Specified by an array, each element of which is a two-element array A *
* with A[0] the name of a section and A[1] the time in seconds at which *
* the section of the video begins. *
***************************************************************************/
var tocData =
[["Prologue", 5],
["Records", 32],
["Weddings", 117],
["The TLA+ Spec", 270.5],
["The Rest of the Spec", 734],
["Checking the Spec", 942],
["Model Values", 1010],
["Correctness of Two-Phase Commit",1167],
["Epilogue", 1248]
] ;
/***************************************************************************
* Items Displayed at Specified Times *
* *
* An array that specifies when items are to be displayed in the Bottom *
* Section of the page. Each element of the array is 3-element array A *
* where A[0] is the id of the item, which is to be displayed from time *
* A[1] through A[2] (in seconds) of the video. *
* *
* The the same id should not appear twice in the ids the elements of *
* timingData, and each of those ids should be the same as the id of one *
* of the <div> elements in in the Bottom Section of the page, which are *
* children the <div> element with id "afterVideo". *
* *
* Note: Putting something at the very end isn't a great idea because on *
* IE, if the user seeks to the end of the video, IE acts as if it's at *
* the beginning and doesn't display something that comes at the end. *
***************************************************************************/
var timingData =
[["begin-title", 0, 5],
["copy-spec", 295.5, 301],
["end-title", 1275, 2000]
] ;
</script>
<script src=tlavideo.js> </script>
<title id="titleId"></title> <!-- title set by createHeading() -->
<!-- The following loads the style sheet for the html files of the videos -->
<link rel="stylesheet" type="text/css" href="tlastyles.css">
</head>
<body onresize="getVideoMag()">
<!--************************************************************************
* The body consists of the following sections: *
* - The heading section. *
* - The video section. *
* - The bottom section. *
*************************************************************************-->
<!--************************************************************************
* The Heading Section *
* *
* It consists of a single <div> element with id "headingId". It contains *
* the name of the lecture. This section is made invisible when the *
* video is in normal playing mode - that is, with videoState = "playing" *
* and timedItemDue = "false". *
*************************************************************************-->
<div id="headingId" style="display:block">
<!-- The lecture name. -->
<div style="float:left;width:335px">
<H1 id="h1Id" style="margin-top:0em;margin-bottom:.5em">
</H1>
</div>
<script> createHeading() </script>
</div>
<!--************************************************************************
* The Video Section *
* *
* This is a <div> item containing two subitems: a <video> item that *
* displays the video and a <div> item that contains the following items: *
* *
* - The controls for the video's playing size. *
* - Controls for skipping backwards and forwards in the video. *
*************************************************************************-->
<div style="display:block;clear:left">
<!--*********************************************************************
* The <video> element. *
**********************************************************************-->
<video onpause="pauseEvent()"
onplay="playEvent()"
onfocus="videoGetsFocus()"
width=450
height=256
controls
preload = "auto"
id="videoId">
<!--********************************************************************
* The src field of the following <source> tag is the URL of the video. *
*********************************************************************-->
<!-- Here is the local copy of version 2 of the video.
<source src= "video6-v2.mp4">
-->
<!-- Here is the copy of the medium-res video for version 2 on Channel 9
<source
src="video6v2.mp4">
-->
<!-- Here is new Channel 9 copy provided by Golnaz Alibeigi -->
<source
src="video6v2.mp4">
<!-- Here are the files for version 1 of the video.
local copy: <source src= "video6.mp4">
channel 9 mid-resolution copy:
<source
src="video6.mp4">
-->
<!-- Here is the local copy of version 1 of the video.
<source src= "video6.mp4">
-->
Your browser cannot display this tutorial because it does not
support the video HTML tag.
</video>
<!--*********************************************************************
* A <div> containing items displayed on a line below the video. *
* *
* One possibility is to remove the controls from the video itself and *
* replace them with the items displayed here plus some other controls. *
* The controls could also be moved to be on top of the video, and to *
* be made visible for a few seconds when the mouse is moved over (and *
* perhaps out of) the video. This would make it possible to prevent *
* the user from putting the video into full-screen mode. *
**********************************************************************-->
<div id="below-video">
<!--*******************************************************************
* A span for showing the controls for skipping forward and back in *
* the video and the "Speed", "Contents" and "How to View" buttons. *
* It is created by a tlavideo.jss function. *
********************************************************************-->
</div>
</div>
<!--************************************************************************
* The Bottom Section *
* *
* A <div> HTML element with id "afterVideo". It normally contains the *
* table of contents when the video is not in normal playing mode. *
* However, at certain parts of the video, it will be replaced by material *
* relevant to that part. That material will consist of a sequence of *
* <div> elements, identified by their ids. *
* *
* The sequence of <div> elements consists of one with id "tocId" followed *
* by a sequence of elements whose ids are in 1-1 correspondence with the *
* ids in timingData. *
*************************************************************************-->
<div id="afterVideo" style="display:block">
<!--*********************************************************************
* A <div> element containing the table of contents, which is created *
* dynamically by the createContents JavaScript function *
**********************************************************************-->
<div id="tocId" style="float:left"></div>
<script> createContents("tocId", tocData) ; </script>
</div>
<div id="rightBottom" style="display:block" >
<!--********************************************************************
* Next comes the sequence of items that are to appear, with the video *
* minimized, at certain points in the video. The timingData variable *
* specifies at what point in the video they appear. *
*********************************************************************-->
<!--*********************************************************************
* This is the call-out to appear at the beginning of the video. *
**********************************************************************-->
<div id = "begin-title" style="float:left">
<div style =
"float:left;margin-left:-20px;font-size:20px;font-family:Calibri">
<h3 class="contents">Lecture 6</h3>
<p style="margin-left:2em;margin-top:-1em;width:15em">
This web page was revised on:<br>
30 August 2021<BR><BR>
Original video was produced on:<br>
12 August 2017 <br>
Corrected version produced on:<br>
14 December 2017 <br>
</p>
</div>
<div id = "item0a" style = "float:left;margin-left:-4em">
<script> createContents("item0a", tocData) ;
</script>
</div>
</div>
<!--********************************************************************
* The "What's wrong with first FillSmall definition" call-out. *
*********************************************************************-->
<!--
<div id = "whats-wrong" style="float:left">
<div style =
"float:left;margin-left:30px;font-size:30px;font-family:Calibri">
<p>
Type a space to stop the video.
</p>
</div>
</div>
-->
<!--********************************************************************
* The "Write Your Definitions " call-out. *
*********************************************************************-->
<!--
<div id = "write-defs" style="float:left">
<div style =
"float:left;margin-top:-15px;margin-left:60px;font-size:30px;font-family:Calibri">
<p>
Stop the video and write<br>
down your definitions.
</p>
</div>
</div>
-->
<!--********************************************************************
* The "Copy Spec" call-out. *
*********************************************************************-->
<div id = "copy-spec" style="float:left; margin-top:20px">
<font style="font-size:17px;font-family:sans-serif">
<div style="width:420px;float:left;margin-left:25px">
Copy the following tiny text, either by
clicking on the <code>Copy</code>
button below it, or by your usual method of copying
text.
<div style="padding-left:5em;padding-top:.5em">
<pre class="copyText" id="bar">
(***************************************************************************)
(* This specification is discussed in "Two-Phase Commit", Lecture 6 of the *)
(* TLA+ Video Course. It describes the Two-Phase Commit protocol, in *)
(* which a transaction manager (TM) coordinates the resource managers *)
(* (RMs) to implement the Transaction Commit specification of module *)
(* TCommit. In this specification, RMs spontaneously issue Prepared *)
(* messages. We ignore the Prepare messages that the TM can send to the *)
(* RMs. *)
(* *)
(* For simplicity, we also eliminate Abort messages sent by an RM when it *)
(* decides to abort. Such a message would cause the TM to abort the *)
(* transaction, an event represented here by the TM spontaneously deciding *)
(* to abort. *)
(***************************************************************************)
CONSTANT RM \* The set of resource managers
VARIABLES
rmState, \* rmState[r] is the state of resource manager r.
tmState, \* The state of the transaction manager.
tmPrepared, \* The set of RMs from which the TM has received "Prepared"
\* messages.
msgs
(***********************************************************************)
(* In the protocol, processes communicate with one another by sending *)
(* messages. For simplicity, we represent message passing with the *)
(* variable msgs whose value is the set of all messages that have been *)
(* sent. A message is sent by adding it to the set msgs. An action *)
(* that, in an implementation, would be enabled by the receipt of a *)
(* certain message is here enabled by the presence of that message in *)
(* msgs. For simplicity, messages are never removed from msgs. This *)
(* allows a single message to be received by multiple receivers. *)
(* Receipt of the same message twice is therefore allowed; but in this *)
(* particular protocol, that's not a problem. *)
(***********************************************************************)
Messages ==
(*************************************************************************)
(* The set of all possible messages. Messages of type "Prepared" are *)
(* sent from the RM indicated by the message's rm field to the TM. *)
(* Messages of type "Commit" and "Abort" are broadcast by the TM, to be *)
(* received by all RMs. The set msgs contains just a single copy of *)
(* such a message. *)
(*************************************************************************)
[type : {"Prepared"}, rm : RM] \cup [type : {"Commit", "Abort"}]
TPTypeOK ==
(*************************************************************************)
(* The type-correctness invariant *)
(*************************************************************************)
/\ rmState \in [RM -> {"working", "prepared", "committed", "aborted"}]
/\ tmState \in {"init", "done"}
/\ tmPrepared \subseteq RM
/\ msgs \subseteq Messages
TPInit ==
(*************************************************************************)
(* The initial predicate. *)
(*************************************************************************)
/\ rmState = [r \in RM |-> "working"]
/\ tmState = "init"
/\ tmPrepared = {}
/\ msgs = {}
-----------------------------------------------------------------------------
(***************************************************************************)
(* We now define the actions that may be performed by the processes, first *)
(* the TM's actions, then the RMs' actions. *)
(***************************************************************************)
TMRcvPrepared(r) ==
(*************************************************************************)
(* The TM receives a "Prepared" message from resource manager r. We *)
(* could add the additional enabling condition r \notin tmPrepared, *)
(* which disables the action if the TM has already received this *)
(* message. But there is no need, because in that case the action has *)
(* no effect; it leaves the state unchanged. *)
(*************************************************************************)
/\ tmState = "init"
/\ [type |-> "Prepared", rm |-> r] \in msgs
/\ tmPrepared' = tmPrepared \cup {r}
/\ UNCHANGED <<rmState, tmState, msgs>>
TMCommit ==
(*************************************************************************)
(* The TM commits the transaction; enabled iff the TM is in its initial *)
(* state and every RM has sent a "Prepared" message. *)
(*************************************************************************)
/\ tmState = "init"
/\ tmPrepared = RM
/\ tmState' = "done"
/\ msgs' = msgs \cup {[type |-> "Commit"]}
/\ UNCHANGED <<rmState, tmPrepared>>
TMAbort ==
(*************************************************************************)
(* The TM spontaneously aborts the transaction. *)
(*************************************************************************)
/\ tmState = "init"
/\ tmState' = "done"
/\ msgs' = msgs \cup {[type |-> "Abort"]}
/\ UNCHANGED <<rmState, tmPrepared>>
RMPrepare(r) ==
(*************************************************************************)
(* Resource manager r prepares. *)
(*************************************************************************)
/\ rmState[r] = "working"
/\ rmState' = [rmState EXCEPT ![r] = "prepared"]
/\ msgs' = msgs \cup {[type |-> "Prepared", rm |-> r]}
/\ UNCHANGED <<tmState, tmPrepared>>
RMChooseToAbort(r) ==
(*************************************************************************)
(* Resource manager r spontaneously decides to abort. As noted above, r *)
(* does not send any message in our simplified spec. *)
(*************************************************************************)
/\ rmState[r] = "working"
/\ rmState' = [rmState EXCEPT ![r] = "aborted"]
/\ UNCHANGED <<tmState, tmPrepared, msgs>>
RMRcvCommitMsg(r) ==
(*************************************************************************)
(* Resource manager r is told by the TM to commit. *)
(*************************************************************************)
/\ [type |-> "Commit"] \in msgs
/\ rmState' = [rmState EXCEPT ![r] = "committed"]
/\ UNCHANGED <<tmState, tmPrepared, msgs>>
RMRcvAbortMsg(r) ==
(*************************************************************************)
(* Resource manager r is told by the TM to abort. *)
(*************************************************************************)
/\ [type |-> "Abort"] \in msgs
/\ rmState' = [rmState EXCEPT ![r] = "aborted"]
/\ UNCHANGED <<tmState, tmPrepared, msgs>>
TPNext ==
\/ TMCommit \/ TMAbort
\/ \E r \in RM :
TMRcvPrepared(r) \/ RMPrepare(r) \/ RMChooseToAbort(r)
\/ RMRcvCommitMsg(r) \/ RMRcvAbortMsg(r)
-----------------------------------------------------------------------------
(***************************************************************************)
(* The material below this point is not discussed in Video Lecture 6. It *)
(* will be explained in Video Lecture 8. *)
(***************************************************************************)
TPSpec == TPInit /\ [][TPNext]_<<rmState, tmState, tmPrepared, msgs>>
(*************************************************************************)
(* The complete spec of the Two-Phase Commit protocol. *)
(*************************************************************************)
THEOREM TPSpec => []TPTypeOK
(*************************************************************************)
(* This theorem asserts that the type-correctness predicate TPTypeOK is *)
(* an invariant of the specification. *)
(*************************************************************************)
-----------------------------------------------------------------------------
(***************************************************************************)
(* We now assert that the Two-Phase Commit protocol implements the *)
(* Transaction Commit protocol of module TCommit. The following statement *)
(* imports all the definitions from module TCommit into the current *)
(* module. *)
(***************************************************************************)
INSTANCE TCommit
THEOREM TPSpec => TCSpec
(*************************************************************************)
(* This theorem asserts that the specification TPSpec of the Two-Phase *)
(* Commit protocol implements the specification TCSpec of the *)
(* Transaction Commit protocol. *)
(*************************************************************************)
(***************************************************************************)
(* The two theorems in this module have been checked with TLC for six *)
(* RMs, a configuration with 50816 reachable states, in a little over a *)
(* minute on a 1 GHz PC. *)
(***************************************************************************)
</pre>
<button class="btn" data-clipboard-target="#bar"
style="margin-top:5px;margin-bottom:10px">
Copy
</button>
</div>
<div style="float:left;width:420px;margin-top:5px">
Then paste the text into the module editor as
the body of specification <code>TwoPhase</code> .
</div>
</div>
</font>
</div>
<!--*********************************************************************
* The display at the end of the video. *
**********************************************************************-->
<div id = "end-title" style="float:left">
<div id = "item0b" style = "float:left">
<script> createContents("item0b", tocData) ; </script>
</div>
<div style =
"float:left;margin-left:10px;font-size:20px;font-family:Calibri">
<h3 class="contents"> The Next Video</h3>
<p style="margin-left:2em;margin-top:-1em;width:15em">
<A href="video7.html">Paxos Commit</a>
</p>
</div>
</div>
<!-- HERE IS AN EXAMPLE OF DISPLAYING TEXT TO BE COPIED
<div id="item3" style="position:relative;top:2em;left:6em;width:60em">
<font style="font-size:17px;font-family:sans-serif">
<div style="width:15em;float:left;">
A tutorial might ask you to copy and paste a specification
like this one:
<div style="padding-left:3em;padding-top:.5em">
<pre class="copyText" id="bar">
MODULE DieHard
(***************************************************************************)
(* In the movie Die Hard J1, the heros must obtain exactly 4 gallons of *)
(* water using a J2 gallon jug, a J1 gallon jug, and a water faucet. Our *)
(* goal: to get TLC to solve the problem for us. *)
(* *)
(* First, we write a spec that describes all allowable behaviors of our *)
(* heros. *)
(***************************************************************************)
EXTENDS Integers
(*************************************************************************)
(* This statement imports the definitions of the ordinary operators on *)
(* integers, such as +. *)
(*************************************************************************)
CONSTANTS J1, J2, G
=============================================================================
</pre>
<button class="btn" data-clipboard-target="#bar">
Copy Text
</button>
</div>
</div>
<div style="float:left;width:20em;padding-left:3em">
Stop the video and copy this specification, either by
clicking on the button or by the usual way of copying
text. If you
paste it into a model editor in the Toolbox, it will appear
in a normal size. If you paste it into another text editor,
you may have to
increase the text's font size to make it readable.
</div>
</font>
</div>
-->
<!-- HERE IS AN EXAMPLE OF OPENING A VIDEO IN A NEW WINDOW
<div id="item2" style="position:relative; top:1em;left:4em">
<div style="text-align:left;width:30em">
<font style="font-size:19px;font-family:sans-serif">
<A href="summary-standalone.pdf" target=_blank>
<b>The TLA+ "Cheat Sheet"</b></font>
</A>
<p style="font-size:18px;font-family:sans-serif">
Left-click to open it in a new window,
or right-click <br> and select
<i>Save as ...</i>
to download it.
</p>
</div>
</div>
-->
<!--**********************************************************************
* This is the end of the sequence of <div> items that are to be *
* displayed at specified points in the video. *
***********************************************************************-->
</div>
</body>
</html>