annotate OrthancStone/Resources/Conventions.txt @ 1515:b750b6eab453

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author Sebastien Jodogne <s.jodogne@gmail.com>
date Tue, 07 Jul 2020 20:52:35 +0200
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1
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2 Some notes about the lifetime of objects
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3 ========================================
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4
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5 Stone applications
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6 ------------------
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7
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8 A typical Stone application can be split in 3 parts:
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9
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10 1- The "loaders part" and the associated "IOracle", that communicate
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11 through "IMessage" objects. The lifetime of these objects is
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12 governed by the "IStoneContext".
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13
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14 2- The "data part" holds the data loaded by the "loaders part". The
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15 related objects must not be aware of the oracle, neither of the
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16 messages. It is up to the user application to store these objects.
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17
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18 3- The "viewport part" is based upon the "Scene2D" class.
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19
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20
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21 Multithreading
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22 --------------
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23
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24 * Stone makes the hypothesis that its objects live in a single thread.
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25 All the content of the "Framework" folder (with the exception of
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26 the "Oracle" stuff) must not use "boost::thread".
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27
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28 * The "IOracleCommand" classes represent commands that must be
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29 executed asynchronously from the Stone thread. Their actual
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30 execution is done by the "IOracle".
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31
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32 * In WebAssembly, the "IOracle" corresponds to the "html5.h"
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33 facilities (notably for the Fetch API). There is no mutex here, as
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34 JavaScript is inherently single-threaded.
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35
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36 * In plain C++ applications, the "IOracle" corresponds to a FIFO queue
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37 of commands that are executed by a pool of threads. The Stone
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38 context holds a global mutex, that must be properly locked by the
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39 user application, and by the "IOracle" when it sends back messages
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40 to the Stone loaders (cf. class "IMessageEmitter").
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41
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42 * Multithreading is thus achieved by defining new oracle commands by
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43 subclassing "IOracleCommand", then by defining a way to execute them
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44 (cf. class "GenericCommandRunner").
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45
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46
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47 References between objects
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48 --------------------------
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49
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50 * An object allocated on the heap must never store a reference/pointer
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51 to another object.
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52
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53 * A class designed to be allocated only on the stack can store a
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54 reference/pointer to another object. Here is the list of
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55 such classes:
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56
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57 - IMessage and its derived classes: All the messages are allocated
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58 on the stack.
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59
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60
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61 Pointers
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62 --------
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63
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64 * As we are targeting C++03 (for VS2008 and LSB compatibility), use
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65 "std::unique_ptr<>" and "boost::shared_ptr<>" (*not*
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66 "std::shared_ptr<>"). We provide an implementation of std::unique_ptr for
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67 pre-C++11 compilers.
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68
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69 * The fact of transfering the ownership of one object to another must
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70 be tagged by naming the method "Acquire...()", and by providing a
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71 raw pointer.
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72
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73 * Use "std::unique_ptr<>" if the goal is to internally store a pointer
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74 whose lifetime corresponds to the host object.
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75
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76 * The use of "boost::weak_ptr<>" should be restricted to
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77 oracle/message handling.
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78
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79 * The use of "boost::shared_ptr<>" should be minimized to avoid
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80 clutter. The "loaders" and "data parts" objects must however
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81 be created as "boost::shared_ptr<>".
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82
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83
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84 Global context
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85 --------------
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86
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87 * As the global Stone context can be created/destroyed by other
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88 languages than C++, we don't use a "boost:shared_ptr<>".