From 0d1cd0d4822628c104890af4c31cdf38c6f96d35 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Tue, 15 Dec 2020 18:30:29 -0700
Subject: use kprotty's ThreadPool implementation (v5)

---
 src/ThreadPool.zig | 116 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 src/ThreadPool.zig

(limited to 'src/ThreadPool.zig')

diff --git a/src/ThreadPool.zig b/src/ThreadPool.zig
new file mode 100644
index 0000000000..a5f59a30e7
--- /dev/null
+++ b/src/ThreadPool.zig
@@ -0,0 +1,116 @@
+const std = @import("std");
+const ThreadPool = @This();
+
+lock: std.Mutex = .{},
+is_running: bool = true,
+allocator: *std.mem.Allocator,
+running: usize = 0,
+threads: []*std.Thread,
+run_queue: RunQueue = .{},
+idle_queue: IdleQueue = .{},
+
+const IdleQueue = std.SinglyLinkedList(std.AutoResetEvent);
+const RunQueue = std.SinglyLinkedList(Runnable);
+const Runnable = struct {
+    runFn: fn (*Runnable) void,
+};
+
+pub fn init(self: *ThreadPool, allocator: *std.mem.Allocator) !void {
+    self.* = .{
+        .allocator = allocator,
+        .threads = &[_]*std.Thread{},
+    };
+
+    errdefer self.deinit();
+
+    var num_threads = std.Thread.cpuCount() catch 1;
+    if (num_threads > 0)
+        self.threads = try allocator.alloc(*std.Thread, num_threads);
+
+    while (num_threads > 0) : (num_threads -= 1) {
+        const thread = try std.Thread.spawn(self, runWorker);
+        self.threads[self.running] = thread;
+        self.running += 1;
+    }
+}
+
+pub fn deinit(self: *ThreadPool) void {
+    self.shutdown();
+
+    std.debug.assert(!self.is_running);
+    for (self.threads[0..self.running]) |thread|
+        thread.wait();
+
+    defer self.threads = &[_]*std.Thread{};
+    if (self.running > 0)
+        self.allocator.free(self.threads);
+}
+
+pub fn shutdown(self: *ThreadPool) void {
+    const held = self.lock.acquire();
+
+    if (!self.is_running)
+        return held.release();
+
+    var idle_queue = self.idle_queue;
+    self.idle_queue = .{};
+    self.is_running = false;
+    held.release();
+
+    while (idle_queue.popFirst()) |idle_node|
+        idle_node.data.set();
+}
+
+pub fn spawn(self: *ThreadPool, comptime func: anytype, args: anytype) !void {
+    const Args = @TypeOf(args);
+    const Closure = struct {
+        arguments: Args,
+        pool: *ThreadPool,
+        run_node: RunQueue.Node = .{ .data = .{ .runFn = runFn } },
+
+        fn runFn(runnable: *Runnable) void {
+            const run_node = @fieldParentPtr(RunQueue.Node, "data", runnable);
+            const closure = @fieldParentPtr(@This(), "run_node", run_node);
+            const result = @call(.{}, func, closure.arguments);
+            closure.pool.allocator.destroy(closure);
+        }
+    };
+
+    const closure = try self.allocator.create(Closure);
+    errdefer self.allocator.destroy(closure);
+    closure.* = .{
+        .arguments = args,
+        .pool = self,
+    };
+
+    const held = self.lock.acquire();
+    self.run_queue.prepend(&closure.run_node);
+
+    const idle_node = self.idle_queue.popFirst();
+    held.release();
+
+    if (idle_node) |node|
+        node.data.set();
+}
+
+fn runWorker(self: *ThreadPool) void {
+    while (true) {
+        const held = self.lock.acquire();
+
+        if (self.run_queue.popFirst()) |run_node| {
+            held.release();
+            (run_node.data.runFn)(&run_node.data);
+            continue;
+        }
+
+        if (!self.is_running) {
+            held.release();
+            return;
+        }
+
+        var idle_node = IdleQueue.Node{ .data = .{} };
+        self.idle_queue.prepend(&idle_node);
+        held.release();
+        idle_node.data.wait();
+    }
+}
-- 
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