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Timestamp:
Nov 6, 2017, 12:23:13 PM (6 years ago)
Author:
Thierry Delisle <tdelisle@…>
Branches:
ADT, aaron-thesis, arm-eh, ast-experimental, cleanup-dtors, deferred_resn, demangler, enum, forall-pointer-decay, jacob/cs343-translation, jenkins-sandbox, master, new-ast, new-ast-unique-expr, new-env, no_list, persistent-indexer, pthread-emulation, qualifiedEnum, resolv-new, with_gc
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b9d0fb6
Parents:
bbeb908
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updated first 3 chapters

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  • doc/proposals/concurrency/text/cforall.tex

    rbbeb908 ra2ea829  
    77The following is a quick introduction to the \CFA language, specifically tailored to the features needed to support concurrency.
    88
    9 \CFA is a extension of ISO-C and therefore supports all of the same paradigms as C. It is a non-object oriented system language, meaning most of the major abstractions have either no runtime overhead or can be opt-out easily. Like C, the basics of \CFA revolve around structures and routines, which are thin abstractions over machine code. The vast majority of the code produced by the \CFA translator respects memory-layouts and calling-conventions laid out by C. Interestingly, while \CFA is not an object-oriented language, lacking the concept of a receiver (e.g., this), it does have some notion of objects\footnote{C defines the term objects as : [Where to I get the C11 reference manual?]}, most importantly construction and destruction of objects. Most of the following code examples can be found on the \CFA website \cite{www-cfa}
     9\CFA is a extension of ISO-C and therefore supports all of the same paradigms as C. It is a non-object oriented system language, meaning most of the major abstractions have either no runtime overhead or can be opt-out easily. Like C, the basics of \CFA revolve around structures and routines, which are thin abstractions over machine code. The vast majority of the code produced by the \CFA translator respects memory-layouts and calling-conventions laid out by C. Interestingly, while \CFA is not an object-oriented language, lacking the concept of a receiver (e.g., this), it does have some notion of objects\footnote{C defines the term objects as : ``region of data storage in the execution environment, the contents of which can represent
     10values''\cite[3.15]{C11}}, most importantly construction and destruction of objects. Most of the following code examples can be found on the \CFA website \cite{www-cfa}
    1011
    1112\section{References}
    1213
    13 Like \CC, \CFA introduces references as an alternative to pointers. In regards to concurrency, the semantics difference between pointers and references are not particularly relevant but since this document uses mostly references here is a quick overview of the semantics :
     14Like \CC, \CFA introduces rebindable references providing multiple dereferecing as an alternative to pointers. In regards to concurrency, the semantic difference between pointers and references are not particularly relevant, but since this document uses mostly references, here is a quick overview of the semantics:
    1415\begin{cfacode}
    1516int x, *p1 = &x, **p2 = &p1, ***p3 = &p2,
    16 &r1 = x,    &&r2 = r1,   &&&r3 = r2;
     17        &r1 = x,    &&r2 = r1,   &&&r3 = r2;
    1718***p3 = 3;                                                      //change x
    1819r3    = 3;                                                      //change x, ***r3
    … …  
    2526sizeof(&ar[1]) == sizeof(int *);        //is true, i.e., the size of a reference
    2627\end{cfacode}
    27 The important thing to take away from this code snippet is that references offer a handle to an object much like pointers but which is automatically derefferenced when convinient.
     28The important take away from this code example is that references offer a handle to an object, much like pointers, but which is automatically dereferenced for convinience.
    2829
    2930\section{Overloading}
    3031
    31 Another important feature of \CFA is function overloading as in Java and \CC, where routine with the same name are selected based on the numbers and type of the arguments. As well, \CFA uses the return type as part of the selection criteria, as in Ada\cite{Ada}. For routines with multiple parameters and returns, the selection is complex.
     32Another important feature of \CFA is function overloading as in Java and \CC, where routines with the same name are selected based on the number and type of the arguments. As well, \CFA uses the return type as part of the selection criteria, as in Ada\cite{Ada}. For routines with multiple parameters and returns, the selection is complex.
    3233\begin{cfacode}
    3334//selection based on type and number of parameters
    … …  
    4546double d = f(4);                //select (2)
    4647\end{cfacode}
    47 This feature is particularly important for concurrency since the runtime system relies on creating different types to represent concurrency objects. Therefore, overloading is necessary to prevent the need for long prefixes and other naming conventions that prevent name clashes. As seen in chapter \ref{basics}, routines main is an example that benefits from overloading.
     48This feature is particularly important for concurrency since the runtime system relies on creating different types to represent concurrency objects. Therefore, overloading is necessary to prevent the need for long prefixes and other naming conventions that prevent name clashes. As seen in chapter \ref{basics}, routine \code{main} is an example that benefits from overloading.
    4849
    4950\section{Operators}
    50 Overloading also extends to operators. The syntax for denoting operator-overloading is to name a routine with the symbol of the operator and question marks where the arguments of the operation would be, like so :
     51Overloading also extends to operators. The syntax for denoting operator-overloading is to name a routine with the symbol of the operator and question marks where the arguments of the operation occur, e.g.:
    5152\begin{cfacode}
    5253int ++? (int op);                       //unary prefix increment
    … …  
    101102
    102103\section{Parametric Polymorphism}
    103 Routines in \CFA can also be reused for multiple types. This is done using the \code{forall} clause which gives \CFA it's name. \code{forall} clauses allow seperatly compiled routines to support generic usage over multiple types. For example, the following sum function will work for any type which support construction from 0 and addition :
     104Routines in \CFA can also be reused for multiple types. This capability is done using the \code{forall} clause which gives \CFA its name. \code{forall} clauses allow separately compiled routines to support generic usage over multiple types. For example, the following sum function works for any type that supports construction from 0 and addition :
    104105\begin{cfacode}
    105106//constraint type, 0 and +
    … …  
    116117\end{cfacode}
    117118
    118 Since writing constraints on types can become cumbersome for more constrained functions, \CFA also has the concept of traits. Traits are named collection of constraints which can be used both instead and in addition to regular constraints:
     119Since writing constraints on types can become cumbersome for more constrained functions, \CFA also has the concept of traits. Traits are named collection of constraints that can be used both instead and in addition to regular constraints:
    119120\begin{cfacode}
    120121trait sumable( otype T ) {
    … …  
    130131
    131132\section{with Clause/Statement}
    132 Since \CFA lacks the concept of a receiver, certain functions end-up needing to repeat variable names often, to solve this \CFA offers the \code{with} statement which opens an aggregate scope making its fields directly accessible (like Pascal).
     133Since \CFA lacks the concept of a receiver, certain functions end-up needing to repeat variable names often. To remove this inconvenience, \CFA provides the \code{with} statement, which opens an aggregate scope making its fields directly accessible (like Pascal).
    133134\begin{cfacode}
    134135struct S { int i, j; };
    135 int mem(S & this) with this             //with clause
     136int mem(S & this) with (this)           //with clause
    136137        i = 1;                                          //this->i
    137138        j = 2;                                          //this->j
    … …  
    140141        struct S1 { ... } s1;
    141142        struct S2 { ... } s2;
    142         with s1                                         //with statement
     143        with (s1)                                       //with statement
    143144        {
    144145                //access fields of s1
    145146                //without qualification
    146                 with s2                                 //nesting
     147                with (s2)                                       //nesting
    147148                {
    148149                        //access fields of s1 and s2
    … …  
    150151                }
    151152        }
    152         with s1, s2                             //scopes open in parallel
     153        with (s1, s2)                           //scopes open in parallel
    153154        {
    154155                //access fields of s1 and s2
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