---
layout: site.njk
title: zul.ThreadPool
---

<h1 id=zul.ThreadPool><a href=#zul.ThreadPool aria-hidden=true>zul.ThreadPool</a></h1>
<p>Lightweight thread pool with back-pressure and zero allocations after initialization.</p>

<p>The standard library's <code>std.Thread.Pool</code> is designed for large jobs. As such, each scheduled job has non-trivial overhead.</p>

<h2 id=example><a href=#example aria-hidden=true>Example</a></h2>
{% highlight zig %}
var tp = try zul.ThreadPool(someTask).init(allocator, .{.count = 4, .backlog = 500});
defer tp.deinit(allocator);

// This will block if the threadpool has 500 pending jobs
// where 500 is the configured backlog
tp.spawn(.{1, true});


fn someTask(i: i32, allow: bool) void {
	// process
}
{% endhighlight %}

<h2 id=ThreadPool><a href=#ThreadPool aria-hidden=true>ThreadPool(fn) struct</a></h2>
<p><code>zul.ThreadPool(comptime Fn: type)</code> is a simple and memory efficient way to have pre-initialized threads ready to process incoming work. The ThreadPool is a generic and takes the function to execute as a parameter.</p>

<h3 id=ThreadPool.methods><a href=#ThreadPool.methods aria-hidden=true>Methods</a></h3>
<div>
	<div class=member>
		<code class=name id=ThreadPool.init><a href=#ThreadPool.init aria-hidden=true>init(...) !*Self</a></code>
{% highlight zig %}
fn init(
	// Allocator is used to create the thread pool, no allocations occur after `init` returns.
	allocator: std.mem.Allocator,

	opts: .{
		// number of threads
		.count: u32 = 1,

		// The number of pending jobs to allow before callers are blocked.
		// The library will allocate an array of this size to hold all pending
		// parameters.
		.backlog: u32 = 500,

	}
) !*ThreadPool(Fn)
{% endhighlight %}
		<div class=desc>
			<p>Creates a <code>zul.ThreadPool(Fn)</code>.</p>
		</div>
	</div>
	<div class=member>
		<code class=name id=ThreadPool.deinit><a href=#ThreadPool.deinit aria-hidden=true>deinit(self: *ThreadPool(Fn)) void</a></code>
		<div class=desc>
			<p>This is method thread-safe. The threads will be stopped and cleaned up.</p>
		</div>
	</div>
	<div class=member>
		<code class=name id=ThreadPool.spawn><a href=#ThreadPool.spawn aria-hidden=true>spawn(self: *ThreadPool(Fn), args: std.meta.ArgsTuple(@TypeOf(Fn))) !void</a></code>
		<div class=desc>
			<p>Enqueues the arguments to be processed by <code>Fn</code> in a worker thread. This call blocks if the number of pending jobs has reached its configured <code>backlog</code>.</p>
		</div>
	</div>
</div>