Ignore:
Timestamp:
Oct 3, 2017, 3:09:12 PM (7 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
Children:
3628765
Parents:
e1ff775
Message:

Added internals section and updated v0.10 up to chapter 4

Location:
doc/proposals/concurrency
Files:
1 added
8 edited

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Unmodified
Added
Removed

  • doc/proposals/concurrency/Makefile

    re1ff775 rdcfc4b35  
    1616text/basics \
    1717text/concurrency \
     18text/internals \
    1819text/parallelism \
    1920text/together \

  • doc/proposals/concurrency/style/cfa-format.tex

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    133133  belowskip=3pt,
    134134  keepspaces=true,
     135  tabsize=4,
    135136  % frame=lines,
    136137  literate=,
    … …  
    150151  keywordstyle=\bfseries\color{blue},
    151152  keywordstyle=[2]\bfseries\color{Plum},
    152   commentstyle=\itshape\color{OliveGreen},                  % green and italic comments
     153  commentstyle=\sf\itshape\color{OliveGreen},             % green and italic comments
    153154  identifierstyle=\color{identifierCol},
    154155  stringstyle=\sf\color{Mahogany},                                % use sanserif font
    … …  
    158159  belowskip=3pt,
    159160  keepspaces=true,
     161  tabsize=4,
    160162  % frame=lines,
    161163  literate=,

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

    re1ff775 rdcfc4b35  
    11% ======================================================================
    22% ======================================================================
    3 \chapter{Basics}\label{basics}
     3\chapter{Concurrency Basics}\label{basics}
    44% ======================================================================
    55% ======================================================================
    6 Before any detailed discussion of the concurrency and parallelism in \CFA, it is important to describe the basics of concurrency and how they are expressed in \CFA user code.
     6Before any detailed discussion of the concurrency and parallelism in \CFA, it is important to describe the basics of concurrency and how they are expressed in \CFA user-code.
    77
    88\section{Basics of concurrency}
    9 At its core, concurrency is based on having call-stacks and potentially multiple threads of execution for these stacks. Concurrency without parallelism only requires having multiple call stacks (or contexts) for a single thread of execution, and switching between these call stacks on a regular basis. A minimal concurrency product can be achieved by creating coroutines, which instead of context switching between each other, always ask an oracle where to context switch next. While coroutines do not technically require a stack, stackfull coroutines are the closest abstraction to a practical "naked"" call stack. When writing concurrency in terms of coroutines, the oracle effectively becomes a scheduler and the whole system now follows a cooperative threading-model \cit. The oracle/scheduler can either be a stackless or stackfull entity and correspondingly require one or two context switches to run a different coroutine. In any case, a subset of concurrency related challenges start to appear. For the complete set of concurrency challenges to occur, the only feature missing is preemption. Indeed, concurrency challenges appear with non-determinism. Guaranteeing mutual-exclusion or synchronisation are simply ways of limiting the lack of determinism in a system. A scheduler introduces order of execution uncertainty, while preemption introduces incertainty about where context-switches occur. Now it is important to understand that uncertainty is not necessarily undesireable; uncertainty can often be used by systems to significantly increase performance and is often the basis of giving a user the illusion that tasks are running in parallel. Optimal performance in concurrent applications is often obtained by having as much non-determinism as correctness allows\cit.
     9At its core, concurrency is based on having multiple call-stacks and scheduling among threads of execution executing on these stacks. Concurrency without parallelism only requires having multiple call stacks (or contexts) for a single thread of execution.
     10
     11Indeed, while execution with a single thread and multiple stacks where the thread is self-scheduling deterministically across the stacks is called coroutining, execution with a single and multiple stacks but where the thread is scheduled by an oracle (non-deterministic from the thread perspective) across the stacks is called concurrency.
     12
     13Therefore, a minimal concurrency system can be achieved by creating coroutines, which instead of context switching among each other, always ask an oracle where to context switch next. While coroutines can execute on the caller's stack-frame, stackfull coroutines allow full generality and are sufficient as the basis for concurrency. The aforementioned oracle is a scheduler and the whole system now follows a cooperative threading-model \cit. The oracle/scheduler can either be a stackless or stackfull entity and correspondingly require one or two context switches to run a different coroutine. In any case, a subset of concurrency related challenges start to appear. For the complete set of concurrency challenges to occur, the only feature missing is preemption. Indeed, concurrency challenges appear with non-determinism. Using mutual-exclusion or synchronisation are ways of limiting the lack of determinism in a system. A scheduler introduces order of execution uncertainty, while preemption introduces uncertainty about where context-switches occur. Now it is important to understand that uncertainty is not undesireable; uncertainty can often be used by systems to significantly increase performance and is often the basis of giving a user the illusion that tasks are running in parallel. Optimal performance in concurrent applications is often obtained by having as much non-determinism as correctness allows\cit.
    1014
    1115\section{\protect\CFA 's Thread Building Blocks}
    12 One of the important features that is missing in C is threading. On modern architectures, a lack of threading is becoming less and less forgivable\cite{Sutter05, Sutter05b}, and therefore modern programming languages must have the proper tools to allow users to write performant concurrent and/or parallel programs. As an extension of C, \CFA needs to express these concepts in a way that is as natural as possible to programmers used to imperative languages. And being a system-level language means programmers expect to choose precisely which features they need and which cost they are willing to pay.
     16One of the important features that is missing in C is threading. On modern architectures, a lack of threading is unacceptable\cite{Sutter05, Sutter05b}, and therefore modern programming languages must have the proper tools to allow users to write performant concurrent and/or parallel programs. As an extension of C, \CFA needs to express these concepts in a way that is as natural as possible to programmers familiar with imperative languages. And being a system-level language means programmers expect to choose precisely which features they need and which cost they are willing to pay.
    1317
    1418\section{Coroutines: A stepping stone}\label{coroutine}
    15 While the main focus of this proposal is concurrency and parallelism, as mentionned above it is important to adress coroutines, which are actually a significant underlying aspect of a concurrency system. Indeed, while having nothing to do with parallelism and arguably little to do with concurrency, coroutines need to deal with context-switchs and other context-management operations. Therefore, this proposal includes coroutines both as an intermediate step for the implementation of threads, and a first class feature of \CFA. Furthermore, many design challenges of threads are at least partially present in designing coroutines, which makes the design effort that much more relevant. The core API of coroutines revolve around two features: independent call stacks and \code{suspend}/\code{resume}.
     19While the main focus of this proposal is concurrency and parallelism, it is important to address coroutines, which are actually a significant building block of a concurrency system. Coroutines need to deal with context-switchs and other context-management operations. Therefore, this proposal includes coroutines both as an intermediate step for the implementation of threads, and a first class feature of \CFA. Furthermore, many design challenges of threads are at least partially present in designing coroutines, which makes the design effort that much more relevant. The core \acrshort{api} of coroutines revolve around two features: independent call stacks and \code{suspend}/\code{resume}.
    1620
    1721Here is an example of a solution to the fibonnaci problem using \CFA coroutines:
    … …  
    5963
    6064\subsection{Construction}
    61 One important design challenge for coroutines and threads (shown in section \ref{threads}) is that the runtime system needs to run code after the user-constructor runs. In the case of coroutines, this challenge is simpler since there is no non-determinism from preemption or scheduling. However, the underlying challenge remains the same for coroutines and threads.
    62 
    63 The runtime system needs to create the coroutine's stack and more importantly prepare it for the first resumption. The timing of the creation is non-trivial since users both expect to have fully constructed objects once execution enters the coroutine main and to be able to resume the coroutine from the constructor. Like for regular objects, constructors can still leak coroutines before they are ready. There are several solutions to this problem but the chosen options effectively forces the design of the coroutine.
     65One important design challenge for coroutines and threads (shown in section \ref{threads}) is that the runtime system needs to run code after the user-constructor runs to connect the object into the system. In the case of coroutines, this challenge is simpler since there is no non-determinism from preemption or scheduling. However, the underlying challenge remains the same for coroutines and threads.
     66
     67The runtime system needs to create the coroutine's stack and more importantly prepare it for the first resumption. The timing of the creation is non-trivial since users both expect to have fully constructed objects once execution enters the coroutine main and to be able to resume the coroutine from the constructor. As regular objects, constructors can leak coroutines before they are ready. There are several solutions to this problem but the chosen options effectively forces the design of the coroutine.
    6468
    6569Furthermore, \CFA faces an extra challenge as polymorphic routines create invisible thunks when casted to non-polymorphic routines and these thunks have function scope. For example, the following code, while looking benign, can run into undefined behaviour because of thunks:
    … …  
    9599}
    96100\end{ccode}
    97 The problem in this example is a race condition between the start of the execution of \code{noop} on the other thread and the stack frame of \code{bar} being destroyed. This extra challenge limits which solutions are viable because storing the function pointer for too long only increases the chances that the race will end in undefined behavior; i.e. the stack based thunk being destroyed before it was used. This challenge is an extension of challenges that come with second-class routines. Indeed, GCC nested routines also have the limitation that the routines cannot be passed outside of the scope of the functions these were declared in. The case of coroutines and threads is simply an extension of this problem to multiple call-stacks.
     101The problem in this example is a storage management issue, the function pointer \code{_thunk0} is only valid until the end of the block. This extra challenge limits which solutions are viable because storing the function pointer for too long causes undefined behavior; i.e. the stack based thunk being destroyed before it was used. This challenge is an extension of challenges that come with second-class routines. Indeed, GCC nested routines also have the limitation that the routines cannot be passed outside of the scope of the functions these were declared in. The case of coroutines and threads is simply an extension of this problem to multiple call-stacks.
    98102
    99103\subsection{Alternative: Composition}
    100 One solution to this challenge would be to use composition/containement,
     104One solution to this challenge is to use composition/containement, where uses add insert a coroutine field which contains the necessary information to manage the coroutine.
    101105
    102106\begin{cfacode}
    103107        struct Fibonacci {
    104               int fn; // used for communication
    105               coroutine c; //composition
     108                int fn; //used for communication
     109                coroutine c; //composition
    106110        };
    107111
    108112        void ?{}(Fibonacci & this) {
    109               this.fn = 0;
    110                 (this.c){};
    111         }
    112 \end{cfacode}
    113 There are two downsides to this approach. The first, which is relatively minor, is that the base class needs to be made aware of the main routine pointer, regardless of whether a parameter or a virtual pointer is used, this means the coroutine data must be made larger to store a value that is actually a compile time constant (address of the main routine). The second problem, which is both subtle and significant, is that now users can get the initialisation order of there coroutines wrong. Indeed, every field of a \CFA struct is constructed but in declaration order, unless users explicitly write otherwise. This semantics means that users who forget to initialize a the coroutine may resume the coroutine with an uninitilized object. For coroutines, this is unlikely to be a problem, for threads however, this is a significant problem.
     113                this.fn = 0;
     114                (this.c){}; //Call constructor to initialize coroutine
     115        }
     116\end{cfacode}
     117There are two downsides to this approach. The first, which is relatively minor, is that the coroutine handle needs to be made aware of the main routine pointer. This requirement means the coroutine data must be made larger to store a value that is actually a compile time constant (address of the main routine). The second problem, which is both subtle and significant, is that now users can get the initialisation order of coroutines wrong. Indeed, every field of a \CFA struct is constructed but in declaration order, unless users explicitly write otherwise. This semantics means that users who forget to initialize the coroutine handle may resume the coroutine with an uninitilized object. For coroutines, this is unlikely to be a problem, for threads however, this is a significant problem.
    114118
    115119\subsection{Alternative: Reserved keyword}
    … …  
    118122\begin{cfacode}
    119123        coroutine Fibonacci {
    120               int fn; // used for communication
     124                int fn; // used for communication
    121125        };
    122126\end{cfacode}
    123 This mean the compiler can solve problems by injecting code where needed. The downside of this approach is that it makes coroutine a special case in the language. Users who would want to extend coroutines or build their own for various reasons can only do so in ways offered by the language. Furthermore, implementing coroutines without language supports also displays the power of \CFA.
    124 While this is ultimately the option used for idiomatic \CFA code, coroutines and threads can both be constructed by users without using the language support. The reserved keywords are only present to improve ease of use for the common cases.
     127This mean the compiler can solve problems by injecting code where needed. The downside of this approach is that it makes coroutine a special case in the language. Users who would want to extend coroutines or build their own for various reasons can only do so in ways offered by the language. Furthermore, implementing coroutines without language supports also displays the power of the programming language used. While this is ultimately the option used for idiomatic \CFA code, coroutines and threads can both be constructed by users without using the language support. The reserved keywords are only present to improve ease of use for the common cases.
    125128
    126129\subsection{Alternative: Lamda Objects}
    … …  
    159162      coroutine_desc * get_coroutine(T & this);
    160163};
    161 \end{cfacode}
    162 This ensures an object is not a coroutine until \code{resume} (or \code{prime}) is called on the object. Correspondingly, any object that is passed to \code{resume} is a coroutine since it must satisfy the \code{is_coroutine} trait to compile. The advantage of this approach is that users can easily create different types of coroutines, for example, changing the memory foot print of a coroutine is trivial when implementing the \code{get_coroutine} routine. The \CFA keyword \code{coroutine} only has the effect of implementing the getter and forward declarations required for users to only have to implement the main routine.
     164
     165forall( dtype T | is_coroutine(T) ) void suspend(T &);
     166forall( dtype T | is_coroutine(T) ) void resume (T &);
     167\end{cfacode}
     168This ensures an object is not a coroutine until \code{resume} is called on the object. Correspondingly, any object that is passed to \code{resume} is a coroutine since it must satisfy the \code{is_coroutine} trait to compile. The advantage of this approach is that users can easily create different types of coroutines, for example, changing the memory layout of a coroutine is trivial when implementing the \code{get_coroutine} routine. The \CFA keyword \code{coroutine} only has the effect of implementing the getter and forward declarations required for users to only have to implement the main routine.
    163169
    164170\begin{center}
    … …  
    186192\end{center}
    187193
    188 The combination of these two approaches allows users new to concurrency to have a easy and concise method while more advanced users can expose themselves to otherwise hidden pitfalls at the benefit of tighter control on memory layout and initialization.
     194The combination of these two approaches allows users new to coroutinning and concurrency to have an easy and concise specification, while more advanced users have tighter control on memory layout and initialization.
    189195
    190196\section{Thread Interface}\label{threads}
    … …  
    205211\end{cfacode}
    206212
    207 Obviously, for this thread implementation to be usefull it must run some user code. Several other threading interfaces use a function-pointer representation as the interface of threads (for example \Csharp~\cite{Csharp} and Scala~\cite{Scala}). However, this proposal considers that statically tying a \code{main} routine to a thread superseeds this approach. Since the \code{main} routine is already a special routine in \CFA (where the program begins), it is possible naturally extend the semantics using overloading to declare mains for different threads (the normal main being the main of the initial thread). As such the \code{main} routine of a thread can be defined as
     213Obviously, for this thread implementation to be usefull it must run some user code. Several other threading interfaces use a function-pointer representation as the interface of threads (for example \Csharp~\cite{Csharp} and Scala~\cite{Scala}). However, this proposal considers that statically tying a \code{main} routine to a thread superseeds this approach. Since the \code{main} routine is already a special routine in \CFA (where the program begins), it is a natural extension of the semantics using overloading to declare mains for different threads (the normal main being the main of the initial thread). As such the \code{main} routine of a thread can be defined as
    208214\begin{cfacode}
    209215        thread foo {};
    … …  
    214220\end{cfacode}
    215221
    216 In this example, threads of type \code{foo} start execution in the \code{void main(foo*)} routine which prints \code{"Hello World!"}. While this proposoal encourages this approach to enforce strongly-typed programming, users may prefer to use the routine based thread semantics for the sake of simplicity. With these semantics it is trivial to write a thread type that takes a function pointer as parameter and executes it on its stack asynchronously
    217 \begin{cfacode}
    218         typedef void (*voidFunc)(void);
     222In this example, threads of type \code{foo} start execution in the \code{void main(foo &)} routine, which prints \code{"Hello World!"}. While this thesis encourages this approach to enforce strongly-typed programming, users may prefer to use the routine-based thread semantics for the sake of simplicity. With these semantics it is trivial to write a thread type that takes a function pointer as a parameter and executes it on its stack asynchronously
     223\begin{cfacode}
     224        typedef void (*voidFunc)(int);
    219225
    220226        thread FuncRunner {
    221227                voidFunc func;
     228                int arg;
    222229        };
    223230
    224         //ctor
    225         void ?{}(FuncRunner & this, voidFunc inFunc) {
     231        void ?{}(FuncRunner & this, voidFunc inFunc, int arg) {
    226232                this.func = inFunc;
    227233        }
    228234
    229         //main
    230235        void main(FuncRunner & this) {
    231                 this.func();
    232         }
    233 \end{cfacode}
    234 
    235 An advantage of the overloading approach to main is to clearly highlight where and what memory is required to pass parameters and return values to/from a thread.
    236 
    237 Of course for threads to be useful, it must be possible to start and stop threads and wait for them to complete execution. While using an \acrshort{api} such as \code{fork} and \code{join} is relatively common in the literature, such an interface is unnecessary. Indeed, the simplest approach is to use \acrshort{raii} principles and have threads \code{fork} once the constructor has completed and \code{join} before the destructor runs.
     236                this.func( this.arg );
     237        }
     238\end{cfacode}
     239
     240An consequence of the strongly typed approach to main is that memory layout of parameters and return values to/from a thread are now explicitly specified in the \acrshort{api}.
     241
     242Of course for threads to be useful, it must be possible to start and stop threads and wait for them to complete execution. While using an \acrshort{api} such as \code{fork} and \code{join} is relatively common in the literature, such an interface is unnecessary. Indeed, the simplest approach is to use \acrshort{raii} principles and have threads \code{fork} after the constructor has completed and \code{join} before the destructor runs.
    238243\begin{cfacode}
    239244thread World;
    … …  
    254259\end{cfacode}
    255260
    256 This semantic has several advantages over explicit semantics typesafety is guaranteed, a thread is always started and stopped exaclty once and users cannot make any progamming errors. Another advantage of this semantic is that it naturally scale to multiple threads meaning basic synchronisation is very simple
     261This semantic has several advantages over explicit semantics: a thread is always started and stopped exaclty once and users cannot make any progamming errors and it naturally scales to multiple threads meaning basic synchronisation is very simple
    257262
    258263\begin{cfacode}
    … …  
    276281\end{cfacode}
    277282
    278 However, one of the apparent drawbacks of this system is that threads now always form a lattice, that is they are always destroyed in opposite order of construction because of block structure. However, storage allocation is not limited to blocks; dynamic allocation can create threads that outlive the scope in which the thread is created much like dynamically allocating memory lets objects outlive the scope in which they are created
     283However, one of the drawbacks of this approach is that threads now always form a lattice, that is they are always destroyed in opposite order of construction because of block structure. This restriction is relaxed by using dynamic allocation, so threads can outlive the scope in which they are created, much like dynamically allocating memory lets objects outlive the scope in which they are created
    279284
    280285\begin{cfacode}
    … …  
    283288};
    284289
    285 //main
    286290void main(MyThread & this) {
    287291        //...
    … …  
    291295        MyThread * long_lived;
    292296        {
     297                //Start a thread at the beginning of the scope
    293298                MyThread short_lived;
    294                 //Start a thread at the beginning of the scope
    295 
    296                 DoStuff();
    297299
    298300                //create another thread that will outlive the thread in this scope
    299301                long_lived = new MyThread;
    300302
     303                DoStuff();
     304
    301305                //Wait for the thread short_lived to finish
    302306        }
    303307        DoMoreStuff();
    304308
    305         //Now wait for the short_lived to finish
     309        //Now wait for the long_lived to finish
    306310        delete long_lived;
    307311}

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

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    55% ======================================================================
    66
    7 As mentionned in the introduction, the document presents the design for the concurrency features in \CFA. Since it is a new language here is a quick review of the 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 much of the same paradigms as C. It is a non-object oriented system level language, meaning it has very most of the major abstractions have either no runtime cost or can be opt-out easily. Like C, the basics of \CFA revolve around structures and routines, which are thin abstractions over assembly. The vast majority of the code produced by a \CFA compiler respects memory-layouts and calling-conventions laid out by C. However, while \CFA is not an object-oriented language according to a strict definition. It does have some notion of objects, most importantly construction and destruction of objects. Most of the following pieces of code can be found as is 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}
    1010
    1111\section{References}
    1212
    13 Like \CC, \CFA introduces references as an alternative to pointers. In regards to concurrency, the semantics difference between pointers and references aren't 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 :
    1414\begin{cfacode}
    1515int x, *p1 = &x, **p2 = &p1, ***p3 = &p2,
    1616&r1 = x,    &&r2 = r1,   &&&r3 = r2;
    17 ***p3 = 3;                              // change x
    18 r3 = 3;                                 // change x, ***r3
    19 **p3 = ...;                             // change p1
    20 &r3 = ...;                              // change r1, (&*)**r3
    21 *p3 = ...;                              // change p2
    22 &&r3 = ...;                             // change r2, (&(&*)*)*r3
    23 &&&r3 = p3;                             // change r3 to p3, (&(&(&*)*)*)r3
    24 int y, z, & ar[3] = { x, y, z };        // initialize array of references
    25 &ar[1] = &z;                            // change reference array element
    26 typeof( ar[1] ) p;                      // is int, i.e., the type of referenced object
    27 typeof( &ar[1] ) q;                     // is int &, i.e., the type of reference
    28 sizeof( ar[1] ) == sizeof( int );       // is true, i.e., the size of referenced object
    29 sizeof( &ar[1] ) == sizeof( int *);     // is true, i.e., the size of a reference
     17***p3 = 3;                                                      //change x
     18r3    = 3;                                                      //change x, ***r3
     19**p3  = ...;                                            //change p1
     20*p3   = ...;                                            //change p2
     21int y, z, & ar[3] = {x, y, z};          //initialize array of references
     22typeof( ar[1]) p;                                       //is int, i.e., the type of referenced object
     23typeof(&ar[1]) q;                                       //is int &, i.e., the type of reference
     24sizeof( ar[1]) == sizeof(int);          //is true, i.e., the size of referenced object
     25sizeof(&ar[1]) == sizeof(int *);        //is true, i.e., the size of a reference
    3026\end{cfacode}
    3127The 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.
    … …  
    3329\section{Overloading}
    3430
    35 Another important feature \CFA has in common with \CC is function overloading :
     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.
    3632\begin{cfacode}
    37 // selection based on type and number of parameters
    38 void f( void );                         // (1)
    39 void f( char );                         // (2)
    40 void f( int, double );                  // (3)
    41 f();                                    // select (1)
    42 f( 'a' );                               // select (2)
    43 f( 3, 5.2 );                            // select (3)
     33//selection based on type and number of parameters
     34void f(void);                   //(1)
     35void f(char);                   //(2)
     36void f(int, double);    //(3)
     37f();                                    //select (1)
     38f('a');                                 //select (2)
     39f(3, 5.2);                              //select (3)
    4440
    45 // selection based on  type and number of returns
    46 char f( int );                          // (1)
    47 double f( int );                        // (2)
    48 [ int, double ] f( int );               // (3)
    49 char c = f( 3 );                        // select (1)
    50 double d = f( 4 );                      // select (2)
    51 [ int, double ] t = f( 5 );             // select (3)
     41//selection based on  type and number of returns
     42char   f(int);                  //(1)
     43double f(int);                  //(2)
     44char   c = f(3);                //select (1)
     45double d = f(4);                //select (2)
    5246\end{cfacode}
    53 This feature is particularly important for concurrency since the runtime system relies on creating different types do represent concurrency objects. Therefore, overloading is necessary to prevent the need for long prefixes and other naming conventions that prevent clashes. As seen in chapter \ref{basics}, the main is an example of routine that benefits from overloading when concurrency in introduced.
     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.
    5448
    5549\section{Operators}
    5650Overloading 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 :
    5751\begin{cfacode}
    58 int ++?( int op );                      // unary prefix increment
    59 int ?++( int op );                      // unary postfix increment
    60 int ?+?( int op1, int op2 );            // binary plus
    61 int ?<=?( int op1, int op2 );           // binary less than
    62 int ?=?( int & op1, int op2 );          // binary assignment
    63 int ?+=?( int & op1, int op2 );         // binary plus-assignment
     52int ++? (int op);                       //unary prefix increment
     53int ?++ (int op);                       //unary postfix increment
     54int ?+? (int op1, int op2);             //binary plus
     55int ?<=?(int op1, int op2);             //binary less than
     56int ?=? (int & op1, int op2);           //binary assignment
     57int ?+=?(int & op1, int op2);           //binary plus-assignment
    6458
    65 struct S { int i, j; };
    66 S ?+?( S op1, S op2 ) {                 // add two structures
    67         return (S){ op1.i + op2.i, op1.j + op2.j };
     59struct S {int i, j;};
     60S ?+?(S op1, S op2) {                           //add two structures
     61        return (S){op1.i + op2.i, op1.j + op2.j};
    6862}
    69 S s1 = { 1, 2 }, s2 = { 2, 3 }, s3;
    70 s3 = s1 + s2;                           // compute sum: s3 == { 2, 5 }
     63S s1 = {1, 2}, s2 = {2, 3}, s3;
     64s3 = s1 + s2;                                           //compute sum: s3 == {2, 5}
    7165\end{cfacode}
    72 
    73 Since concurrency does not use operator overloading, this feature is more important as an introduction for the syntax of constructors.
     66While concurrency does not use operator overloading directly, this feature is more important as an introduction for the syntax of constructors.
    7467
    7568\section{Constructors/Destructors}
    76 Object life time is often a challenge in concurrency. \CFA uses the approach of giving concurrent meaning to object life time as a mean of synchronization and/or mutual exclusion. Since \CFA relies heavily on the life time of objects, Constructors \& Destructors are a the core of the features required for concurrency and parallelism. \CFA uses the following syntax for constructors and destructors :
     69Object life-time is often a challenge in concurrency. \CFA uses the approach of giving concurrent meaning to object life-time as a mean of synchronization and/or mutual exclusion. Since \CFA relies heavily on the life time of objects, constructors and destructors are a core feature required for concurrency and parallelism. \CFA uses the following syntax for constructors and destructors :
    7770\begin{cfacode}
    7871struct S {
    … …  
    8073        int * ia;
    8174};
    82 void ?{}( S & s, int asize ) with s {   // constructor operator
    83         size = asize;                   // initialize fields
    84         ia = calloc( size, sizeof( S ) );
     75void ?{}(S & s, int asize) {    //constructor operator
     76        s.size = asize;                         //initialize fields
     77        s.ia = calloc(size, sizeof(S));
    8578}
    86 void ^?{}( S & s ) with s {             // destructor operator
    87         free( ia );                     // de-initialization fields
     79void ^?{}(S & s) {                              //destructor operator
     80        free(ia);                                       //de-initialization fields
    8881}
    8982int main() {
    90         S x = { 10 }, y = { 100 };      // implict calls: ?{}( x, 10 ), ?{}( y, 100 )
    91         ...                             // use x and y
    92         ^x{};  ^y{};                    // explicit calls to de-initialize
    93         x{ 20 };  y{ 200 };             // explicit calls to reinitialize
    94         ...                             // reuse x and y
    95 }                                       // implict calls: ^?{}( y ), ^?{}( x )
     83        S x = {10}, y = {100};          //implict calls: ?{}(x, 10), ?{}(y, 100)
     84        ...                                                     //use x and y
     85        ^x{};  ^y{};                            //explicit calls to de-initialize
     86        x{20};  y{200};                         //explicit calls to reinitialize
     87        ...                                                     //reuse x and y
     88}                                                               //implict calls: ^?{}(y), ^?{}(x)
    9689\end{cfacode}
    97 The language guarantees that every object and all their fields are constructed. Like \CC construction is automatically done on declaration and destruction done when the declared variables reach the end of its scope.
     90The language guarantees that every object and all their fields are constructed. Like \CC, construction of an object is automatically done on allocation and destruction of the object is done on deallocation. Allocation and deallocation can occur on the stack or on the heap.
     91\begin{cfacode}
     92{
     93        struct S s = {10};      //allocation, call constructor
     94        ...
     95}                                               //deallocation, call destructor
     96struct S * s = new();   //allocation, call constructor
     97...
     98delete(s);                              //deallocation, call destructor
     99\end{cfacode}
     100Note that like \CC, \CFA introduces \code{new} and \code{delete}, which behave like \code{malloc} and \code{free} in addition to constructing and destructing objects, after calling \code{malloc} and before calling \code{free} respectively.
    98101
    99 For more information see \cite{cforall-ug,rob-thesis,www-cfa}.
     102For more information on \CFA see \cite{cforall-ug,rob-thesis,www-cfa}.

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

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    700700\end{tabular}
    701701\end{center}
    702 This method is more constrained and explicit, which may help users tone down the undeterministic nature of concurrency. Indeed, as the following examples demonstrates, external scheduling allows users to wait for events from other threads without the concern of unrelated events occuring. External scheduling can generally be done either in terms of control flow (e.g., \uC) or in terms of data (e.g. Go). Of course, both of these paradigms have their own strenghts and weaknesses but for this project control-flow semantics were chosen to stay consistent with the rest of the languages semantics. Two challenges specific to \CFA arise when trying to add external scheduling with loose object definitions and multi-monitor routines. The previous example shows a simple use \code{_Accept} versus \code{wait}/\code{signal} and its advantages. Note that while other languages often use \code{accept} as the core external scheduling keyword, \CFA uses \code{waitfor} to prevent name collisions with existing socket APIs.
     702This method is more constrained and explicit, which may help users tone down the undeterministic nature of concurrency. Indeed, as the following examples demonstrates, external scheduling allows users to wait for events from other threads without the concern of unrelated events occuring. External scheduling can generally be done either in terms of control flow (e.g., \uC) or in terms of data (e.g. Go). Of course, both of these paradigms have their own strenghts and weaknesses but for this project control-flow semantics were chosen to stay consistent with the rest of the languages semantics. Two challenges specific to \CFA arise when trying to add external scheduling with loose object definitions and multi-monitor routines. The previous example shows a simple use \code{_Accept} versus \code{wait}/\code{signal} and its advantages. Note that while other languages often use \code{accept} as the core external scheduling keyword, \CFA uses \code{waitfor} to prevent name collisions with existing socket \acrshort{api}s.
    703703
    704704In the case of internal scheduling, the call to \code{wait} only guarantees that \code{V} is the last routine to access the monitor. This entails that the routine \code{V} may have acquired mutual exclusion several times while routine \code{P} was waiting. On the other hand, external scheduling guarantees that while routine \code{P} was waiting, no routine other than \code{V} could acquire the monitor.

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

    re1ff775 rdcfc4b35  
    33% ======================================================================
    44
    5 This proposal provides a minimal concurrency API that is simple, efficient and can be reused to build higher-level features. The simplest possible concurrency system is a thread and a lock but this low-level approach is hard to master. An easier approach for users is to support higher-level constructs as the basis of the concurrency, in \CFA. Indeed, for highly productive concurrent programming, high-level approaches are much more popular~\cite{HPP:Study}. Examples are task based, message passing and implicit threading. Therefore a high-level approach is adopted in \CFA
     5This thesis provides a minimal concurrency \acrshort{api} that is simple, efficient and can be reused to build higher-level features. The simplest possible concurrency system is a thread and a lock but this low-level approach is hard to master. An easier approach for users is to support higher-level constructs as the basis of concurrency. Indeed, for highly productive concurrent programming, high-level approaches are much more popular~\cite{HPP:Study}. Examples are task based, message passing and implicit threading. The high-level approach and its minimal \acrshort{api} are tested in a dialect of C, call \CFA. [Is there value to say that this thesis is also an early definition of the \CFA language and library in regards to concurrency?]
    66
    7 There are actually two problems that need to be solved in the design of concurrency for a programming language: which concurrency and which parallelism tools are available to the programmers. While these two concepts are often combined, they are in fact distinct, requiring different tools~\cite{Buhr05a}. Concurrency tools need to handle mutual exclusion and synchronization, while parallelism tools are about performance, cost and resource utilization.
     7There are actually two problems that need to be solved in the design of concurrency for a programming language: which concurrency and which parallelism tools are available to the programmer. While these two concepts are often combined, they are in fact distinct, requiring different tools~\cite{Buhr05a}. Concurrency tools need to handle mutual exclusion and synchronization, while parallelism tools are about performance, cost and resource utilization.

  • doc/proposals/concurrency/thesis.tex

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    103103\input{parallelism}
    104104
     105\input{internals}
     106
    105107\input{together}
    106108

  • doc/proposals/concurrency/version

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    1 0.10.2
     10.10.33
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