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

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    3 \chapter{Cforall Overview}
     3\chapter{Cforall crash course}
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    66
    7 The following is a quick introduction to the \CFA language, specifically tailored to the features needed to support concurrency.
     7This thesis presents the design for a set of concurrency features in \CFA. Since it is a new dialect of C, the following is a quick introduction to the 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 : ``region of data storage in the execution environment, the contents of which can represent
    10 values''\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}
     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 received (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 pieces of code can be found on the \CFA website \cite{www-cfa}
    1110
    1211\section{References}
    1312
    14 Like \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:
     13Like \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 :
    1514\begin{cfacode}
    1615int x, *p1 = &x, **p2 = &p1, ***p3 = &p2,
    17         &r1 = x,    &&r2 = r1,   &&&r3 = r2;
     16&r1 = x,    &&r2 = r1,   &&&r3 = r2;
    1817***p3 = 3;                                                      //change x
    1918r3    = 3;                                                      //change x, ***r3
    … …  
    2625sizeof(&ar[1]) == sizeof(int *);        //is true, i.e., the size of a reference
    2726\end{cfacode}
    28 The 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.
     27The 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.
    2928
    3029\section{Overloading}
    3130
    32 Another 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.
     31Another 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.
    3332\begin{cfacode}
    3433//selection based on type and number of parameters
    … …  
    4645double d = f(4);                //select (2)
    4746\end{cfacode}
    48 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}, routine \code{main} is an example that benefits from overloading.
     47This 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.
    4948
    5049\section{Operators}
    51 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 occur, e.g.:
     50Overloading 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 :
    5251\begin{cfacode}
    5352int ++? (int op);                       //unary prefix increment
    … …  
    102101
    103102\section{Parametric Polymorphism}
    104 Routines 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 :
     103Routines 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 :
    105104\begin{cfacode}
    106105//constraint type, 0 and +
    … …  
    117116\end{cfacode}
    118117
    119 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 that can be used both instead and in addition to regular constraints:
     118Since 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:
    120119\begin{cfacode}
    121120trait sumable( otype T ) {
    … …  
    131130
    132131\section{with Clause/Statement}
    133 Since \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).
     132Since \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).
    134133\begin{cfacode}
    135134struct S { int i, j; };
    136 int mem(S & this) with (this)           //with clause
     135int mem(S & this) with this             //with clause
    137136        i = 1;                                          //this->i
    138137        j = 2;                                          //this->j
    … …  
    141140        struct S1 { ... } s1;
    142141        struct S2 { ... } s2;
    143         with (s1)                                       //with statement
     142        with s1                                         //with statement
    144143        {
    145144                //access fields of s1
    146145                //without qualification
    147                 with (s2)                                       //nesting
     146                with s2                                 //nesting
    148147                {
    149148                        //access fields of s1 and s2
    … …  
    151150                }
    152151        }
    153         with (s1, s2)                           //scopes open in parallel
     152        with s1, s2                             //scopes open in parallel
    154153        {
    155154                //access fields of s1 and s2
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