github.com/AR1011/wazero@v1.0.5/site/content/languages/_index.md (about)

     1  +++
     2  title = "Languages"
     3  layout = "single"
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     5  
     6  WebAssembly has a virtual machine architecture where the host is the embedding
     7  process and the guest is a program compiled into the WebAssembly Binary Format,
     8  also known as Wasm. The first step is to take a source file and compile it into
     9  the Wasm bytecode.
    10  
    11  e.g. If your source is in Go, you might compile it with TinyGo.
    12  
    13  ```goat
    14      .-----------.    .----------------------.      .-----------.
    15     /  main.go  /---->|  tinygo -target=wasi +---->/ main.wasm /
    16    '-----+-----'      '----------------------'    '-----------'
    17  ```
    18  
    19  Below are notes wazero contributed so far, in alphabetical order by language.
    20  
    21  - [Go]({{< relref "/go.md" >}}) e.g. `GOOS=js GOARCH=wasm go build -o X.wasm X.go`
    22  - [TinyGo]({{< relref "/tinygo.md" >}}) e.g. `tinygo build -o X.wasm -target=wasi X.go`
    23  - [Rust]({{< relref "/rust.md" >}}) e.g. `rustc -o X.wasm --target wasm32-wasi X.rs`
    24  - [Zig]({{< relref "/zig.md" >}}) e.g. `zig build-exe X.zig -target wasm32-wasi`
    25  
    26  wazero is a runtime that embeds in Go applications, not a web browser. As
    27  such, these notes bias towards backend use of WebAssembly, not browser use.
    28  
    29  Disclaimer: These are not official documentation, nor represent the teams who
    30  maintain language compilers. If you see any errors, please help [maintain][1]
    31  these and [star our GitHub repository][2] if they are helpful. Together, we can
    32  make WebAssembly easier on the next person.
    33  
    34  ## Constraints
    35  
    36  The [WebAssembly Core specification]({{< ref "/specs#core" >}}) defines a
    37  stack-based virtual machine. The only features that work by default are
    38  computational in nature, and the only way to communicate is via functions,
    39  memory or global variables.
    40  
    41  WebAssembly has no standard library or system call interface to implement
    42  features the operating system would otherwise provide. Certain capabilities,
    43  such as forking a process, will not work. Support of common I/O features, such
    44  as writing to the console, vary. See [System Calls](#system-calls) for more.
    45  
    46  Software is more than technical constraints. WebAssembly remains a relatively
    47  niche target, with limited maintenance and development. This means that certain
    48  features may not work, yet, even if they could technically.
    49  
    50  In general, developing with WebAssembly is difficult, and fewer problems can
    51  be discovered at compilation time vs more supported targets. This results in
    52  more runtime errors, or even panics. Where error messages exist, they may be
    53  misleading. Finally, the languages maintainers may be less familiar with how to
    54  solve the problems, and/or rely on less available key maintainers.
    55  
    56  ### Mitigating Constraints
    57  
    58  The above constraints affect the library design and dependency choices in your
    59  source, and by extension the choices of library dependencies you can use. In
    60  extreme cases, constraints or support concerns may lead developers to choose
    61  newer languages like [Zig][10].
    62  
    63  Regardless of the programming language used, the best advice is to unit test
    64  your code, and run tests with your intended WebAssembly runtime, like wazero.
    65  
    66  These tests should cover the critical paths of your code, including errors.
    67  Doing so protects your time. You'll have higher confidence, and more efficient
    68  means to communicate problems vs ad-hoc reports.
    69  
    70  ## System Calls
    71  
    72  WebAssembly is a stack-based virtual machine specification, so operates at a
    73  lower level than an operating system. For functionality the operating system
    74  would otherwise provide, system interfaces are needed.
    75  
    76  Programming languages usually include a standard library, with features that
    77  require I/O, such as writing to the console. Portability is helped along with
    78  [POSIX][3] conforming implementations of system calls, such as `fd_read`.
    79  
    80  There is a [WebAssembly System Interface]({{< ref "/specs#wasi" >}}), a.k.a.
    81  WASI, which defines host functions loosely based on POSIX. There's also a
    82  de facto implementation [wasi-libc][4]. However, WASI is not a standard and
    83  language compilers don't always support it.
    84  
    85  For example, AssemblyScript once supported WASI, but no longer does. Even
    86  compilers that target WASI using [wasi-libc][4] have gaps. For example,
    87  [TinyGo]({{< relref "/tinygo.md" >}}) does not yet support `fd_readdir`. Some toolchains have a
    88  hybrid approach. For example, Emscripten uses WASI for console output, but its
    89  own virtual filesystem functions. Finally, the team behind WASI are
    90  developing an incompatible, modular replacement to the current version.
    91  
    92  It is important to note that even when system interfaces are supported, some
    93  users prefer a freestanding compilation target that restricts them. This helps
    94  them control binary size and performance.
    95  
    96  In summary, system interfaces in WebAssembly are not standard and are immature.
    97  Developers need to understand and test the system interfaces they rely on.
    98  Testing ensures not only the present capabilities, but also they continue to
    99  operate as the ecosystem matures.
   100  
   101  ## Concurrency
   102  
   103  WebAssembly does not yet support true parallelism; it lacks support for
   104  multiple threads, atomics, and memory barriers. (It may someday; See
   105  the [threads proposal][5].)
   106  
   107  For example, a compiler targeting [WASI]({{< ref "/specs#wasi" >}}), generates
   108  a `_start` function corresponding to `main` in the original source code. When
   109  the WebAssembly runtime calls `_start`, it remains on the same thread of
   110  execution until that function completes.
   111  
   112  Concretely, if using wazero, a Wasm function call remains on the calling
   113  goroutine until it completes.
   114  
   115  In summary, while true that host functions can do anything, including launch
   116  processes, Wasm binaries compliant with the [WebAssembly Core Specification]
   117  ({{< ref "/specs#core" >}}) cannot do anything in parallel, unless they use
   118  non-standard instructions or conventions not yet defined by the specification.
   119  
   120  ### Compiling Parallel Code to Serial Wasm
   121  
   122  Until this [changes][5], language compilers cannot generate Wasm that can
   123  control scheduling within a function or safely modify memory in parallel.
   124  In other words, one function cannot do anything in parallel.
   125  
   126  This impacts how programming language primitives translate to Wasm:
   127  
   128  - Garbage collection invokes on the runtime host's calling thread instead of
   129    in the background.
   130  - Language-defined threads or co-routines fail compilation or are limited to
   131    sequential processing.
   132  - Locks and barriers fail compilation or are implemented unsafely.
   133  - Async functions including I/O execute sequentially.
   134  
   135  Language compilers often used shared infrastructure, such as [LLVM][6] and
   136  [Binaryen][7]. One tool that helps in translation is Binaryen's [Asyncify][8],
   137  which lets a language support synchronous operations in an async manner.
   138  
   139  ### Concurrency via Orchestration
   140  
   141  To work around lack of concurrency at the WebAssembly Core abstraction, tools
   142  often orchestrate pools of workers, and ensure a module in that pool is only
   143  used sequentially.
   144  
   145  For example, [waPC][9] provides a WASM module pool, so host callbacks can be
   146  invoked in parallel, despite not being able to share memory.
   147  
   148  [1]: https://github.com/AR1011/wazero/tree/main/site/content/languages
   149  [2]: https://github.com/AR1011/wazero/stargazers
   150  [3]: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/contents.html
   151  [4]: https://github.com/WebAssembly/wasi-libc
   152  [5]: https://github.com/WebAssembly/threads
   153  [6]: https://llvm.org
   154  [7]: https://github.com/WebAssembly/binaryen
   155  [8]: https://github.com/WebAssembly/binaryen/blob/main/src/passes/Asyncify.cpp
   156  [9]: https://github.com/wapc/wapc-go
   157  [10]: https://ziglang.org/