Causeway

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<pre>
<pre>
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$ cd e/src
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$ cd e/src/esrc/scripts
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$ rune -De.home=esrc esrc/scripts/causeway.e-swt
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$ rune causeway.e-swt
</pre>
</pre>
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From the Welcome view select an example program from the Help menu.
From the Welcome view select an example program from the Help menu.
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<pre>
<pre>
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$ rune -De.home=esrc -Dsrc=<srcRootDir> esrc/scripts/causeway.e-swt <logs>
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$ rune -Dsrc=<srcRootDir> causeway.e-swt <logs>...
</pre>
</pre>
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<pre>
<pre>
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-J-Xss128m -J-Xmx128m
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$ rune -J-Xss128m -J-Xmx128m causeway.e-swt
</pre>
</pre>
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Setting Causeway's debug flag enables a Debug view. As events are selected in the viewer, the Debug view shows the corresponding trace record in the log file.
 
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<pre>
 
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-Dcauseway_debug=true
 
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</pre>
 
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[[Image:debug-view.png]]
 
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== Waterken Example (Ajax-style) ==
== Waterken Example (Ajax-style) ==
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* Search view (leftmost): This view lists bookmarks and results of search commands.
* Search view (leftmost): This view lists bookmarks and results of search commands.
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* Process-order view: This view lists events in chronological order, organized by vat. For example, clicking the "buyer" tab shows all events logged by the buyer vat. The events are ordered by turn number and within each turn, anchor number.
+
* Process-order view: This view lists events in chronological order, organized by vat. For example, clicking the "buyer" tab shows all events logged by the buyer vat. The events are ordered by turn number and within each turn, an intra-turn number.
* Message-order view: This view shows the order in which events caused other events by sending messages. Message order is reflected in the outline structure: nested events were caused by the parent event. Causeway assigns each vat a color so we can see when message flow crosses vat boundaries.  
* Message-order view: This view shows the order in which events caused other events by sending messages. Message order is reflected in the outline structure: nested events were caused by the parent event. Causeway assigns each vat a color so we can see when message flow crosses vat boundaries.  
* Stack Explorer and Source view: These views are familiar from sequential debugging.
* Stack Explorer and Source view: These views are familiar from sequential debugging.
-
 
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Individual tree items represent events and their descriptive labels depend on the information available in the trace record for the event. Causeway labels the tree items according to the following priority.
 
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# The "text" field string. This field is required for Comment records. It is optional for Sent, SentIf, and Resolved records.
 
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# If the trace record has at least one stack trace with a source and span, a single line of source code from the source file specified in the top stack entry.
 
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# If there's no span, source file name and function name specified in the top stack entry.
 
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# If nothing else, a Causeway comment.
 
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=== Menu Commands ===
=== Menu Commands ===
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'''Search >> Find Lost Messages''' reports sent messages that were not received. The message graph is searched for <tt>Sent</tt> or <tt>SentIf</tt> events having no corresponding <tt>Got</tt> event. Of course, the message may actually have been received, but the event was not logged.
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'''Search >> Find Lost Messages''' reports sent messages that were apparently not received.
-
 
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'''Tools >> Set Filter Options...''' presents all source files seen during parsing of the trace logs. Individual files can be filtered out.
'''Tools >> Set Filter Options...''' presents all source files seen during parsing of the trace logs. Individual files can be filtered out.
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''(Limitation: These settings are not persistent across launches.)''
 
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[[Image:filter-options.png|alt=Filter options dialog]]
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[[Image:filter-async-and.png|alt=Filter options dialog]]
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=== Context Menu Commands ===
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Filtering <code>AsyncAnd.java</code> hides all stack frames whose source is in the <code>AsyncAnd</code> class, resulting in simpler, more abstract message-order view and GraphViz graph (as shown below).
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'''Bookmark''' bookmarks the currently selected event.
 
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[[Image:filtered-mov.png|alt=Message-order view with AsyncAnd.java filter]]
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[[Image:bookmark.png|alt=Bookmark menu item]]
 
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[[Image:filtered-mg.png|alt=Message graph with AsyncAnd.java filter]]
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'''Find Multiples''' finds the multiple causes of a joining event.
 
 +
''(Limitation: These settings are not persistent across launches.)''
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[[Image:find-multiples.png|alt=Find multiples menu item]]
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=== Context Menu Commands ===
 +
'''Bookmark''' bookmarks the currently selected event.
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'''Search Stacks'''
 
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[[Image:bookmark.png|alt=Bookmark menu item]]
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[[Image:search-stacks.png|alt=Search stacks menu item]]
 
 +
'''Find Multiples''' finds the multiple causes of a joining event, e.g., finds the multiple sends to a target showing a multiples icon.
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''(Limitation: Not all source lines ... and currently, there is no visual indication...)''
 
 +
[[Image:find-multiples.png|alt=Find multiples menu item]]
 +
'''Search Stacks''' finds all events that contain a stack frame for this source line, e.g., all events passing through this source code.
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== Causeway's Trace Log Format ==
 
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Causeway supports the [http://waterken.sourceforge.net/debug/ JSON trace log format] defined by Tyler Close.
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[[Image:search-stacks.png|alt=Search stacks menu item]]
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[[Image:event-types.png|alt=Trace log event types]]
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When causality tracing is on the events are logged as follows.
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{| border="1"
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! Event !!    Record type
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|-
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| An eventual send to an object || Sent
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|-
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| A message delivery, starting a new turn || Got
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|-
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| Registration of a when-block, to execute when a promise resolves || SentIf
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|-
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| Returned result from a remote object, for local promise resolution || Returned
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|-
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| A state-based event contributes to promise resolution || Progressed
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|-
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| A promise resolves || Fulfilled or Rejected
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|-
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| Programmer logs a comment || Comment
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|}
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=== Logging Ajax-style Messaging in Waterken ===
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Consider the sequence of events shown below.
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[[Image:part-in-stock.png|alt=Ajax-style message send]]
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* a remote inventory object is queried for the availability of a part
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* the inventory object reports true to <code>teller</code>, a callback object
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The eventual send to the inventory object has two log entries: a <tt>Sent</tt> and its corresponding <tt>Got</tt>.
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<pre>
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    "class" : [ "org.ref_send.log.Sent", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 3,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/",
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        "number" : 3
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      }
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    },
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    "message" : "lqhjpwbbeemozk-2-0",
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    "timestamp" : 1274238401772,
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    "trace" : {
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      "calls" : [ {
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          "name" : "Main.Buy.fulfill",
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          "source" : "org/waterken/purchase_ajax/Main.java",
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          "span" : [ [ 68 ] ]
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        }, {
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          "name" : "Main.Buy.fulfill",
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          "source" : "org/waterken/purchase_ajax/Main.java",
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          "span" : [ [ 48 ] ]
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        } ]
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    }
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</pre>
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The <tt>anchor</tt> uniquely identifies the origin of this message send as the 3rd messaging event from the buyer vat, turn 3.
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The <tt>message</tt> is a generated string which uniquely identifies a message.
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The <tt>trace</tt> is the stack capture at the point of the message send.
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Note: The <tt>loop</tt> field identifies the vat by URI. By convention, Causeway picks up the part following "/-/", in this case buyer, for a short display name.
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Note: The <tt>timestamp</tt> field is optional. Currently, it is ignored by Causeway, so it's not shown in the remaining trace records.
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<pre>
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    "class" : [ "org.ref_send.log.Got", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 1,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/product/",
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        "number" : 2
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      }
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    },
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    "message" : "lqhjpwbbeemozk-2-0",
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    "trace" : {
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      "calls" : [ {
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          "name" : "InventoryMaker.InventoryX.partInStock",
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          "source" : "org/waterken/purchase_ajax/InventoryMaker.java"
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        } ]
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    }
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</pre>
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The corresponding <tt>Got</tt> record matches on <tt>message</tt>. The message delivery in the product vat starts a new turn, turn 2.
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Being at the top of a new turn, there is limited stack capture and getting a source span through Java reflection, is not practical.
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-
 
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Reporting true to <tt>teller</tt> has two log entries: a <tt>Sent</tt> and its corresponding <tt>Got</tt>.
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<pre>
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    "class" : [ "org.ref_send.log.Sent", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 2,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/product/",
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        "number" : 2
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      }
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    },
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    "message" : "ewrigzpctikrhk-1-0",
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    "trace" : {
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      "calls" : [ {
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          "name" : "InventoryMaker.InventoryX.partInStock",
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          "source" : "org/waterken/purchase_ajax/InventoryMaker.java",
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          "span" : [ [ 19 ] ]
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-
        } ]
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    }
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-
</pre>
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-
 
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The <tt>anchor</tt> uniquely identifies the origin of this message send as the 2nd messaging event from the product vat, turn 2.
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-
 
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<pre>
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    "class" : [ "org.ref_send.log.Got", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 1,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/",
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        "number" : 10
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      }
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    },
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    "message" : "ewrigzpctikrhk-1-0",
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    "trace" : {
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      "calls" : [ {
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          "name" : "AsyncAnd.run",
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          "source" : "org/waterken/purchase_ajax/AsyncAnd.java"
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        } ]
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    }
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-
</pre>
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-
 
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The corresponding <tt>Got</tt> record matches on <tt>message</tt>. The message delivery in the buyer vat starts a new turn, turn 10.
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-
 
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=== Logging Promise-based Messaging in Waterken ===
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Consider the sequence of events shown below.
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[[Image:promise-part-in-stock.png|alt=Promise-based message send]]
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Note: For the purpose of describing the trace records the screenshot shows events that actually will be filtered by Causeway and do not appear in the message-order view.
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<pre>
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  "class" : [ "org.ref_send.log.Sent", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 1,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/",
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        "number" : 2
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      }
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    },
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    "message" : "3t4ubiwssjzuy2-2-0",
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    "trace" : {
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      "calls" : [ {
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          "name" : "Buyer.Buy.fulfill",
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          "source" : "org/waterken/purchase_promise/Buyer.java",
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          "span" : [ [ 39 ] ]
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        }, {
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          "name" : "Buyer.Buy.fulfill",
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          "source" : "org/waterken/purchase_promise/Buyer.java",
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          "span" : [ [ 24 ] ]
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        } ]
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    }
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</pre>
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<pre>
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    "class" : [ "org.ref_send.log.Got", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 0,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/product/",
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        "number" : 1
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      }
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    },
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    "message" : "3t4ubiwssjzuy2-2-0",
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    "trace" : {
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      "calls" : [ {
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          "name" : "InventoryMaker.InventoryX.partInStock",
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          "source" : "org/waterken/purchase_promise/InventoryMaker.java"
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        } ]
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    }
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</pre>
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<pre>
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    "class" : [ "org.ref_send.log.Returned", "org.ref_send.log.Sent", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 1,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/product/",
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        "number" : 1
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      }
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    },
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    "message" : "3t4ubiwssjzuy2-2-0-return"
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</pre>
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<pre>
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    "class" : [ "org.ref_send.log.Got", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 0,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/",
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        "number" : 5
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      }
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    },
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    "message" : "3t4ubiwssjzuy2-2-0-return"
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</pre>
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<pre>
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    "class" : [ "org.ref_send.log.Fulfilled", "org.ref_send.log.Resolved", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 1,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/",
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        "number" : 5
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      }
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    },
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    "condition" : "http://localhost:8080/-/buyer/#p3"
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-
</pre>
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<pre>
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    "class" : [ "org.ref_send.log.Got", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 0,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/",
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        "number" : 8
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      }
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    },
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    "message" : "http://localhost:8080/-/buyer/#w3",
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    "trace" : {
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      "calls" : [ {
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          "name" : "AsyncAnd.DoAnswer.fulfill",
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          "source" : "org/waterken/purchase_promise/AsyncAnd.java"
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        } ]
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    }
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</pre>
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-
 
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<pre>
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    "class" : [ "org.ref_send.log.Progressed", "org.ref_send.log.Resolved", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 1,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/",
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        "number" : 8
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      }
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    },
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    "condition" : "http://localhost:8080/-/buyer/#p6",
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    "trace" : {
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      "calls" : [ {
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          "name" : "AsyncAnd.DoAnswer.fulfill",
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          "source" : "org/waterken/purchase_promise/AsyncAnd.java",
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          "span" : [ [ 34 ] ]
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        }, {
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          "name" : "AsyncAnd.DoAnswer.fulfill",
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          "source" : "org/waterken/purchase_promise/AsyncAnd.java",
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          "span" : [ [ 16 ] ]
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        } ]
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    }
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</pre>
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<pre>
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    "class" : [ "org.ref_send.log.Got", "org.ref_send.log.Event" ],
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    "anchor" : {
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      "number" : 0,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/",
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        "number" : 14
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      }
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    },
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    "message" : "http://localhost:8080/-/buyer/#w6",
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    "trace" : {
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      "calls" : [ {
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          "name" : "Buyer.CheckAnswers.fulfill",
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          "source" : "org/waterken/purchase_promise/Buyer.java"
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        } ]
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    }
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</pre>
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-
 
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-
The registration of when-blocks, logged as <tt>SentIf<tt> records, are filtered from the message-order view, as they don't contribute to the understanding of message flow. They do appear in process-order, as shown below.
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[[Image:buyer-po-view.png|alt=Buyer events in process order]]
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-
 
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<pre>
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    "class" : [ "org.ref_send.log.SentIf", "org.ref_send.log.Sent", "org.ref_send.log.Event" ],
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    "anchor" : {
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-
      "number" : 7,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/",
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        "number" : 2
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      }
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    },
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    "condition" : "http://localhost:8080/-/buyer/#p6",
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    "message" : "http://localhost:8080/-/buyer/#w6",
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    "trace" : {
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      "calls" : [ {
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          "name" : "Buyer.Buy.fulfill",
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          "source" : "org/waterken/purchase_promise/Buyer.java",
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          "span" : [ [ 46 ] ]
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        }, {
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          "name" : "Buyer.Buy.fulfill",
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          "source" : "org/waterken/purchase_promise/Buyer.java",
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          "span" : [ [ 24 ] ]
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-
        } ]
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    }
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</pre>
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-
 
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<pre>
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    "class" : [ "org.ref_send.log.SentIf", "org.ref_send.log.Sent", "org.ref_send.log.Event" ],
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    "anchor" : {
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-
      "number" : 4,
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      "turn" : {
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        "loop" : "http://localhost:8080/-/buyer/",
+
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        "number" : 2
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      }
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    },
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    "condition" : "http://localhost:8080/-/buyer/#p3",
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    "message" : "http://localhost:8080/-/buyer/#w3",
+
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    "trace" : {
+
-
      "calls" : [ {
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          "name" : "AsyncAnd.run",
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          "source" : "org/waterken/purchase_promise/AsyncAnd.java",
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          "span" : [ [ 60 ] ]
+
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        }, {
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          "name" : "Buyer.Buy.fulfill",
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          "source" : "org/waterken/purchase_promise/Buyer.java",
+
-
          "span" : [ [ 43 ] ]
+
-
        }, {
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          "name" : "Buyer.Buy.fulfill",
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          "source" : "org/waterken/purchase_promise/Buyer.java",
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          "span" : [ [ 24 ] ]
+
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        } ]
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    }
+
-
</pre>
+
-
 
+
-
 
+
-
=== Performance Issues in Waterken ===
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-
 
+
-
Due to the expense of stack capture in Java, tracing in Waterken incurs roughly, an order of magnitude performance penalty. If tracing is off, there is no penalty.
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-
 
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Waterken guarantees message order delivery and if a connection is dropped, there's enough information to know about partial success. For example, if 2 messages (msg1, msg2) are sent from vat A to vat B, they are guaranteed to be processed in the order sent. If the connection is dropped after msg1 is successfully sent, when the connection is re-established, it is known that only msg2 must be resent.
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The identifiers used to support these guarantees are also used for tracing. The advantage of these multi-purpose identifiers is there is no overhead when tracing is off (i.e., unique message identifiers, just for tracing, are not sent out over the wire.)
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Note: Resending a message after a connection is re-established can result in 2 identical <tt>Sent</tt> events being logged. Causeway notices when the event records are identical and ignores the duplicate.
 
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''(Limitation: Matching events must match exactly on source and line position as specified in the trace logs. Not all lines in the source view can be searched and currently, there is no visual indication identifying the lines that can be searched.)''
== See Also ==
== See Also ==
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Our current development effort is to generalize Causeway to support asynchronous message-passing programs running on event loop-based platforms in general, not just '''''E'''''. Our initial focus has been on the Waterken server.
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[[Causeway Platform Developer]] to understand how to instrument a platform to generate Causeway trace logs.
[http://www.hpl.hp.com/techreports/2009/HPL-2009-78.html HP Labs Technical Report] presents our experience with the Waterken web server which we have instrumented to generate Causeway's language-neutral trace log format.
[http://www.hpl.hp.com/techreports/2009/HPL-2009-78.html HP Labs Technical Report] presents our experience with the Waterken web server which we have instrumented to generate Causeway's language-neutral trace log format.

Latest revision as of 22:50, 26 May 2010

Contents

Causeway: A message-oriented distributed debugger

Causeway is an open source postmortem distributed debugger for examining the behavior of distributed programs built as communicating event loops. Its message-oriented approach follows the flow of messages across process and machine boundaries.

Getting Started

The simplest way to get started is to launch Causeway from a command line shell and then open one of the examples.

$ cd e/src/esrc/scripts
$ rune causeway.e-swt

From the Welcome view select an example program from the Help menu.


Image:Welcome-help.png


Optionally, the sources and trace logs can be specified on the command line.

$ rune -Dsrc=<srcRootDir> causeway.e-swt <logs>...

Java's default memory settings are sufficient for the examples but larger programs need more stack and heap space. Use the -Xss (stack) and -Xmx (heap) options to increase Java default memory sizes. Follow the amount with m for Mb or k for Kb. Notice the format does not follow the name=value convention. The J option tells rune to pass the option to Java.

$ rune -J-Xss128m -J-Xmx128m causeway.e-swt 

Waterken Example (Ajax-style)

This Java program ran on the Waterken server instrumented to generate Causeway's trace log format. The program is a distributed implementation of a procedure for handling new purchase orders.

Before an order is placed, certain conditions must be met: the item is in stock and available, the customer’s account is in good standing, and the delivery options are up to date. An object residing in the “buyer” process (or vat) has remote references to objects residing in the “product” and “accounts” processes. The buyer queries the remote objects with asynchronous message sends. This example uses Ajax-style continuation-passing: a request carries a callback argument to which a response should be sent.

The screenshot below shows the principal views from Causeway's postmortem display for this example.

Causeway Viewer

Causeway Viewer


  • Search view (leftmost): This view lists bookmarks and results of search commands.
  • Process-order view: This view lists events in chronological order, organized by vat. For example, clicking the "buyer" tab shows all events logged by the buyer vat. The events are ordered by turn number and within each turn, an intra-turn number.
  • Message-order view: This view shows the order in which events caused other events by sending messages. Message order is reflected in the outline structure: nested events were caused by the parent event. Causeway assigns each vat a color so we can see when message flow crosses vat boundaries.
  • Stack Explorer and Source view: These views are familiar from sequential debugging.

Menu Commands

File >> Set Source Root... point at the root directory of the sources.

For example, for the trace record pathname shown below,

"trace" : {
  "calls" : [ {
      "name" : "AsyncAnd.run",
      "source" : "org/waterken/purchase_ajax/AsyncAnd.java"
    } ]
}

set the source root to the underlined prefix.

~/Desktop/waterken/example/src/org/waterken/purchase_ajax/AsyncAnd.java

(Limitation: Cannot set multiple source roots.)


File >> Open select log files to open.

(Limitation: Cannot select a folder. Must go into the folder and select the multiple files.)


File >> Export... translates Causeway's message graph (DAG) to the GraphViz DOT format and writes the dot file to a local disk. The dot file is a human-readable text file. It specifies a graph using the DOT language. GraphViz must be downloaded and installed to see the graph visualization. The graph below was generated for the Waterken example described above.


Causeway's DAG as GraphViz graph


Search >> Find Lost Messages reports sent messages that were apparently not received.

Tools >> Set Filter Options... presents all source files seen during parsing of the trace logs. Individual files can be filtered out.


Filter options dialog


Filtering AsyncAnd.java hides all stack frames whose source is in the AsyncAnd class, resulting in simpler, more abstract message-order view and GraphViz graph (as shown below).


Message-order view with AsyncAnd.java filter


Message graph with AsyncAnd.java filter


(Limitation: These settings are not persistent across launches.)

Context Menu Commands

Bookmark bookmarks the currently selected event.


Bookmark menu item


Find Multiples finds the multiple causes of a joining event, e.g., finds the multiple sends to a target showing a multiples icon.


Find multiples menu item


Search Stacks finds all events that contain a stack frame for this source line, e.g., all events passing through this source code.


Search stacks menu item


(Limitation: Matching events must match exactly on source and line position as specified in the trace logs. Not all lines in the source view can be searched and currently, there is no visual indication identifying the lines that can be searched.)

See Also

Causeway Platform Developer to understand how to instrument a platform to generate Causeway trace logs.

HP Labs Technical Report presents our experience with the Waterken web server which we have instrumented to generate Causeway's language-neutral trace log format.

Screencast presents a brief demonstration of Causeway, using the example from the HP Tech Report.

Debugging a Waterken application explains how to configure the Waterken server to emit the JSON debugging records understood by Causeway.

Debugging AmbientTalk using Causeway explains how to emit Causeway debugging records, in order to use Causeway to debug AmbientTalk applications.

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