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  • doc/theses/colby_parsons_MMAth/text/intro.tex

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    7 Concurrent programs are the wild west of programming because determinism and simple ordering of program operations go out the window.
    8 To seize the reins and write performant and safe concurrent code, high-level concurrent-language features are needed.
    9 Like any other craftsmen, programmers are only as good as their tools, and concurrent tooling and features are no exception.
     7Concurrent programs are the wild west of programming because determinism and simple ordering of program operations go out the window. 
     8To seize the reins and write performant and safe concurrent code, high-level concurrent-language features are needed. 
     9Like any other craftsmen, programmers are only as good as their tools, and concurrent tooling and features are no exception. 
    1010
    11 This thesis presents a suite of high-level concurrent-language features implemented in the new programming-language \CFA.
    12 These features aim to improve the performance of concurrent programs, aid in writing safe programs, and assist user productivity by improving the ease of concurrent programming.
    13 The groundwork for concurrent features in \CFA was designed and implemented by Thierry Delisle~\cite{Delisle18}, who contributed the threading system, coroutines, monitors and other basic concurrency tools.
    14 This thesis builds on top of that foundation by providing a suite of high-level concurrent features.
    15 The features include a @mutex@ statement, channels, a @waituntil@ statement, and an actor system.
    16 All of these features exist in other programming languages in some shape or form;
    17 however, this thesis extends the original ideas by improving performance, productivity, and safety.
     11This thesis presents a suite of high-level concurrent-language features implemented in the new programming-language \CFA.
     12These features aim to improve the performance of concurrent programs, aid in writing safe programs, and assist user productivity by improving the ease of concurrent programming.
     13The groundwork for concurrent features in \CFA was implemented by Thierry Delisle~\cite{Delisle18}, who contributed the threading system, coroutines, monitors and other tools.
     14This thesis builds on top of that foundation by providing a suite of high-level concurrent features.
     15The features include a @mutex@ statement, channels, a @waituntil@ statement, and an actor system.
     16All of these features exist in other programming languages in some shape or form, however this thesis extends the original ideas by improving performance, productivity, and safety.
    1817
    1918\section{The Need For Concurrent Features}
     19Asking a programmer to write a complex concurrent program without any concurrent language features is asking them to undertake a very difficult task.
     20They would only be able to rely on the atomicity that their hardware provides and would have to build up from there.
     21This would be like asking a programmer to write a complex sequential program only in assembly.
     22Both are doable, but would often be easier and less error prone with higher level tooling.
    2023
    21 % Asking a programmer to write a complex concurrent program without any concurrent language features is asking them to undertake a very difficult task.
    22 % They would only be able to rely on the atomicity that their hardware provides and would have to build up from there.
    23 % This would be like asking a programmer to write a complex sequential program only in assembly.
    24 % Both are doable, but would often be easier and less error prone with higher level tooling.
     24Concurrent programming has many pitfalls that are unique and do not show up in sequential code:
     25\begin{enumerate}
     26\item Deadlock, where threads cyclically wait on resources, blocking them indefinitely.
     27\item Livelock, where threads constantly attempt a concurrent operation unsuccessfully, resulting in no progress being made.
     28\item Race conditions, where thread orderings can result in differing behaviours and correctness of a program execution.
     29\item Starvation, where threads may be deprived of access to some shared resource due to unfairness and never make progress.
     30\end{enumerate}
     31Even with the guiding hand of concurrent tools these pitfalls can still catch unwary programmers, but good language support can prevent, detect, and mitigate these problems.
    2532
    26 Concurrent programming has many unique pitfalls that do not appear in sequential programming:
    27 \begin{enumerate}
    28 \item Race conditions, where thread orderings can result in arbitrary behaviours, resulting in correctness problems.
    29 \item Livelock, where threads constantly attempt a concurrent operation unsuccessfully, resulting in no progress being made.
    30 \item Starvation, where \emph{some} threads constantly attempt a concurrent operation unsuccessfully, resulting in partial progress being made.
    31 \item Deadlock, where some threads wait for an event that cannot occur, blocking them indefinitely, resulting in no progress being made.
    32 \end{enumerate}
    33 Even with the guiding hand of concurrent tools these pitfalls still catch unwary programmers, but good language support helps significantly to prevent, detect, and mitigate these problems.
     33\section{A Brief Overview}
    3434
    35 \section{Thesis Overview}
    36 
    37 Chapter~\ref{s:cfa} of this thesis aims to familiarize the reader with the language \CFA.
    38 In this chapter, syntax and features of the \CFA language that appear in this work are discussed.
    39 Chapter~\ref{s:cfa_concurrency} briefly discusses prior concurrency work in \CFA, and how the work in this thesis builds on top of the existing framework.
    40 Each remaining chapter introduces an additional \CFA concurrent-language feature, which includes discussing prior related work for the feature, extensions over prior features, and uses benchmarks to compare the performance the feature with corresponding or similar features in other languages and systems.
    41 
    42 Chapter~\ref{s:mutexstmt} discusses the @mutex@ statement, a language feature that provides safe and simple lock usage.
    43 The @mutex@ statement is compared both in terms of safety and performance with similar mechanisms in \CC and Java.
    44 Chapter~\ref{s:channels} discusses channels, a message passing concurrency primitive that provides for safe synchronous and asynchronous communication among threads.
    45 Channels in \CFA are compared to Go's channels, which popularized the use of channels in modern concurrent programs.
    46 Chapter~\ref{s:actors} discusses the \CFA actor system.
    47 An actor system is a close cousin of channels, as it also belongs to the message passing paradigm of concurrency.
    48 However, an actor system provides a greater degree of abstraction and ease of scalability, making it useful for a different range of problems than channels.
    49 The actor system in \CFA is compared with a variety of other systems on a suite of benchmarks.
    50 Chapter~\ref{s:waituntil} discusses the \CFA @waituntil@ statement, which provides the ability to synchronize while waiting for a resource, such as acquiring a lock, accessing a future, or writing to a channel.
    51 The \CFA @waituntil@ statement provides greater flexibility and expressibility than similar features in other languages.
    52 All in all, the features presented aim to fill in gaps in the current \CFA concurrent-language support, enabling users to write a wider range of complex concurrent programs with ease.
     35The first chapter of this thesis aims to familiarize the reader with the language \CFA.
     36In this chapter, syntax and features of the \CFA language that appear in this work are discussed The next chapter briefly discusses prior concurrency work in \CFA and how this work builds on top of existing features.
     37The remaining chapters each introduce a concurrent language feature, discuss prior related work, and present contributions which are then benchmarked against other languages and systems.
     38The first of these chapters discusses the @mutex@ statement, a language feature that improves ease of use and safety of lock usage.
     39The @mutex@ statement is compared both in terms of safety and performance with similar tools in \CC and Java.
     40The following chapter discusses channels, a message passing concurrency primitive that provides an avenue for safe synchronous and asynchronous communication across threads.
     41Channels in \CFA are compared to Go, which popularized the use of channels in modern concurrent programs.
     42The following chapter discusses the \CFA actor system.
     43The \CFA actor system is a close cousin of channels, as it also belongs to the message passing paradigm of concurrency.
     44However, the actor system provides a great degree of abstraction and ease of scalability, making it useful for a different range of problems than channels.
     45The actor system in \CFA is compared with a variety of other systems on a suite of benchmarks, where it achieves significant performance gains over other systems due to its design.
     46The final chapter discusses the \CFA @waituntil@ statement which provides the ability to synchronize while waiting for a resource, such as acquiring a lock, accessing a future, or writing to a channel.
     47The @waituntil@ statement presented provides greater flexibility and expressibility than similar features in other languages.
     48All in all, the features presented aim to fill in gaps in the current \CFA concurrent language support, and enable users to write a wider range of complex concurrent programs with ease.
    5349
    5450\section{Contributions}
    55 This work presents the following contributions within each of the additional language features:
    56 \begin{enumerate}[leftmargin=*]
    57 \item The @mutex@ statement that:
    58     \begin{itemize}[itemsep=0pt]
    59     \item
    60     provides deadlock-free multiple lock acquisition,
    61     \item
    62     clearly denotes lock acquisition and release,
    63     \item
    64     and has good performance irrespective of lock ordering.
    65     \end{itemize}
    66 \item The channel that:
     51This work presents the following contributions:
     52\begin{enumerate}
     53\item The @mutex@ statement which:
     54\begin{itemize}[itemsep=0pt]
     55\item
     56provides deadlock-free multiple lock acquisition,
     57\item
     58clearly denotes lock acquisition and release,
     59\item
     60and has good performance irrespective of lock ordering.
     61\end{itemize}
     62\item Channels which:
    6763\begin{itemize}[itemsep=0pt]
    6864    \item
     
    7571    and provides toggle-able statistics for performance tuning.
    7672\end{itemize}
    77 \item The in-memory actor system that:
     73\item An in-memory actor system that:
    7874\begin{itemize}[itemsep=0pt]
    7975    \item
     
    8682    gains performance through static-typed message sends, eliminating the need for dynamic dispatch,
    8783    \item
    88     introduces the copy queue, an array-based queue specialized for the actor use-case to minimize calls to the memory allocator,
     84    introduces the copy queue, an array based queue specialized for the actor use case to minimize calls to the memory allocator,
    8985    \item
    9086    has robust detection of six tricky, but common actor programming errors,
     
    9490    and provides toggle-able statistics for performance tuning.
    9591\end{itemize}
    96 \item The @waituntil@ statement that:
     92
     93\item A @waituntil@ statement which:
    9794\begin{itemize}[itemsep=0pt]
    9895    \item
    9996    is the only known polymorphic synchronous multiplexing language feature,
    10097    \item
    101     provides greater expressibility for waiting conditions than other languages,
     98    provides greater expressibility of waiting conditions than other languages,
    10299    \item
    103     and achieves comparable performance to similar features in two other languages.
     100    and achieves comparable performance to similar features in two other languages,
    104101\end{itemize}
    105102\end{enumerate}
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