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| UML2 Sequence Diagram Framework | Event matching and trace synchronization | |
CTF is a format used to store traces. It is self defining, binary and made to be easy to write to. Before going further, the full specification of the CTF file format can be found at http://www.efficios.com/ .
For the purpose of the reader some basic description will be given. A CTF trace typically is made of several files all in the same folder.
These files can be split into two types:
The metadata is either raw text or packetized text. It is TSDL encoded. it contains a description of the type of data in the event streams. It can grow over time if new events are added to a trace but it will never overwrite what is already there.
The event streams are a file per stream per cpu. These streams are binary and packet based. The streams store events and event information (ie lost events) The event data is stored in headers and field payloads.
So if you have two streams (channels) "channel1" and "channel2" and 4 cores, you will have the following files in your trace directory: "channel1_0" , "channel1_1" , "channel1_2" , "channel1_3" , "channel2_0" , "channel2_1" , "channel2_2" & "channel2_3"
In order to read a CTF trace, two steps must be done.
The metadata is a written in a subset of the C language called TSDL. To read it, first it is depacketized (if it is not in plain text) then the raw text is parsed by an antlr grammar. The parsing is done in two phases. There is a lexer (CTFLexer.g) which separated the metatdata text into tokens. The tokens are then pattern matched using the parser (CTFParser.g) to form an AST. This AST is walked through using "IOStructGen.java" to populate streams and traces in trace parent object.
When the metadata is loaded and read, the trace object will be populated with 3 items:
Now all the trace readers for the event streams have everything they need to read a trace. They will each point to one file, and read the file from packet to packet. Every time the trace reader changes packet, the index is updated with the new packet's information. The readers are in a priority queue and sorted by timestamp. This ensures that the events are read in a sequential order. They are also sorted by file name so that in the eventuality that two events occur at the same time, they stay in the same order.
The reason for maintaining an index is to speed up seeks. In the case that a user wishes to seek to a certain timestamp, they just have to find the index entry that contains the timestamp, and go there to iterate in that packet until the proper event is found. this will reduce the searches time by an order of 8000 for a 256k packet size (kernel default).
The trace can be read easily now but the data is still awkward to extract.
A location in a given trace, it is currently the timestamp of a trace and the index of the event. The index shows for a given timestamp if it is the first second or nth element.
The CtfTmfTrace is a wrapper for the standard CTF trace that allows it to perform the following actions:
The CtfIterator is a wrapper to the CTF file reader. It behaves like an iterator on a trace. However, it contains a file pointer and thus cannot be duplicated too often or the system will run out of file handles. To alleviate the situation, a pool of iterators is created at the very beginning and stored in the CtfTmfTrace. They can be retried by calling the GetIterator() method.
Since each CtfIterator will have a file reader, the OS will run out of handles if too many iterators are spawned. The solution is to use the iterator manager. This will allow the user to get an iterator. If there is a context at the requested position, the manager will return that one, if not, a context will be selected at random and set to the correct location. Using random replacement minimizes contention as it will settle quickly at a new balance point.
The CtfTmfContext implements the ITmfContext type. It is the CTF equivalent of TmfContext. It has a CtfLocation and points to an iterator in the CtfTmfTrace iterator pool as well as the parent trace. it is made to be cloned easily and not affect system resources much. Contexts behave much like C file pointers (FILE*) but they can be copied until one runs out of RAM.
The CtfTmfTimestamp take a CTF time (normally a long int) and outputs the time formats it as a TmfTimestamp, allowing it to be compared to other timestamps. The time is stored with the UTC offset already applied. It also features a simple toString() function that allows it to output the time in more Human readable ways: "yyyy/mm/dd/hh:mm:ss.nnnnnnnnn ns" for example. An additional feature is the getDelta() function that allows two timestamps to be substracted, showing the time difference between A and B.
The CtfTmfEvent is an ITmfEvent that is used to wrap event declarations and event definitions from the CTF side into easier to read and parse chunks of information. It is a final class with final fields made to be newed very often without incurring performance costs. Most of the information is already available. It should be noted that one type of event can appear called "lost event" these are synthetic events that do not exist in the trace. They will not appear in other trace readers such as babeltrace.
There are other helper files that format given events for views, they are simpler and the architecture does not depend on them.
For the moment live CTF trace reading is not supported.
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| UML2 Sequence Diagram Framework | Event matching and trace synchronization |