Add a synchronous signal handler for graceful shutdown

src/Sighandler.zig

@@ -0,0 +1,107 @@
+// Copyright (C) 2023-2025  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+//! This structure processes operating system signals (SIGINT, SIGTERM)
+//! and runs callbacks to clean up the system gracefully.
+//!
+//! The structure does not clear the memory allocated in the arena,
+//! clear the entire arena when exiting the program.
+const std = @import("std");
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+const lp = @import("lightpanda");
+
+const log = lp.log;
+
+const SigHandler = @This();
+
+arena: Allocator,
+
+sigset: std.posix.sigset_t = undefined,
+handle_thread: ?std.Thread = null,
+
+attempt: u32 = 0,
+listeners: std.ArrayList(Listener) = .empty,
+
+pub const Listener = struct {
+    args: []const u8,
+    start: *const fn (context: *const anyopaque) void,
+};
+
+pub fn install(self: *SigHandler) !void {
+    // Block SIGINT and SIGTERM for the current thread and all created from it
+    self.sigset = std.posix.sigemptyset();
+    std.posix.sigaddset(&self.sigset, std.posix.SIG.INT);
+    std.posix.sigaddset(&self.sigset, std.posix.SIG.TERM);
+    std.posix.sigaddset(&self.sigset, std.posix.SIG.QUIT);
+    std.posix.sigprocmask(std.posix.SIG.BLOCK, &self.sigset, null);
+
+    self.handle_thread = try std.Thread.spawn(.{ .allocator = self.arena }, SigHandler.sighandle, .{self});
+    self.handle_thread.?.detach();
+}
+
+pub fn on(self: *SigHandler, func: anytype, args: std.meta.ArgsTuple(@TypeOf(func))) !void {
+    assert(@typeInfo(@TypeOf(func)).@"fn".return_type.? == void);
+
+    const Args = @TypeOf(args);
+    const TypeErased = struct {
+        fn start(context: *const anyopaque) void {
+            const args_casted: *const Args = @ptrCast(@alignCast(context));
+            @call(.auto, func, args_casted.*);
+        }
+    };
+
+    const buffer = try self.arena.alignedAlloc(u8, .of(Args), @sizeOf(Args));
+    errdefer self.arena.free(buffer);
+
+    const bytes: []const u8 = @ptrCast((&args)[0..1]);
+    @memcpy(buffer, bytes);
+
+    try self.listeners.append(self.arena, .{
+        .args = buffer,
+        .start = TypeErased.start,
+    });
+}
+
+fn sighandle(self: *SigHandler) noreturn {
+    while (true) {
+        var sig: c_int = 0;
+
+        const rc = std.c.sigwait(&self.sigset, &sig);
+        if (rc != 0) {
+            log.err(.app, "Unable to process signal {}", .{rc});
+            std.process.exit(1);
+        }
+
+        switch (sig) {
+            std.posix.SIG.INT, std.posix.SIG.TERM => {
+                if (self.attempt > 1) {
+                    std.process.exit(1);
+                }
+                self.attempt += 1;
+
+                log.info(.app, "Received termination signal...", .{});
+                for (self.listeners.items) |*item| {
+                    item.start(item.args.ptr);
+                }
+                continue;
+            },
+            else => continue,
+        }
+    }
+}