feat(channel): impl peek()

build.zig

@@ -27,18 +27,21 @@ pub fn build(b: *std.Build) void {
     // This declares intent for the library to be installed into the standard
     // location when the user invokes the "install" step (the default step when
     // running `zig build`).
-    lib.install();
+    b.installArtifact(lib);
 
-    // Creates a step for unit testing.
+    // Creates a step for unit testing. This only builds the test executable
+    // but does not run it.
     const main_tests = b.addTest(.{
-        .root_source_file = .{ .path = "src/main.zig" },
+        .root_source_file = .{ .path = "src/lib.zig" },
         .target = target,
         .optimize = optimize,
     });
 
+    const run_main_tests = b.addRunArtifact(main_tests);
+
     // This creates a build step. It will be visible in the `zig build --help` menu,
     // and can be selected like this: `zig build test`
     // This will evaluate the `test` step rather than the default, which is "install".
     const test_step = b.step("test", "Run library tests");
-    test_step.dependOn(&main_tests.step);
+    test_step.dependOn(&run_main_tests.step);
 }

src/lib.zig

@@ -78,6 +78,16 @@ fn Channel(comptime T: type) type {
             return value;
         }
 
+        pub fn peek(self: *const Self) ?T {
+            const read_idx = self.read.load(.Acquire);
+            const write_idx = self.write.load(.Acquire);
+
+            if (read_idx == write_idx) return null;
+
+            std.atomic.fence(.Acquire);
+            return self.buf[self.mask(read_idx)];
+        }
+
         pub fn len(self: *const Self) Index {
             const read_idx = self.read.load(.Acquire);
             const write_idx = self.write.load(.Acquire);
@@ -109,7 +119,7 @@ pub fn RingBuffer(comptime T: type) type {
             std.debug.assert(std.math.isPowerOfTwo(buf.len)); // capacity must be a power of two
             std.debug.assert(buf.len <= max_capacity);
 
-            std.mem.set(T, buf, 0);
+            @memset(buf, 0);
 
             return .{ .read = 0, .write = 0, .buf = buf };
         }