From 375caac5019aa174cf33b537335a085f43a2407d Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Mon, 13 May 2024 13:12:40 -0400
Subject: sighook: New utilities for hooking signals

This allows multiple hooks to be installed for a single signal.
---
 tests/sighook.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 tests/sighook.c

(limited to 'tests/sighook.c')

diff --git a/tests/sighook.c b/tests/sighook.c
new file mode 100644
index 0000000..e5dd47f
--- /dev/null
+++ b/tests/sighook.c
@@ -0,0 +1,97 @@
+// Copyright © Tavian Barnes <tavianator@tavianator.com>
+// SPDX-License-Identifier: 0BSD
+
+#include "prelude.h"
+#include "tests.h"
+#include "sighook.h"
+#include "atomic.h"
+#include "thread.h"
+#include <pthread.h>
+#include <signal.h>
+#include <sys/time.h>
+
+static atomic size_t count = 0;
+
+/** SIGALRM handler. */
+static void alrm_hook(int sig, siginfo_t *info, void *arg) {
+	fetch_add(&count, 1, relaxed);
+}
+
+/** Swap out an old hook for a new hook. */
+static int swap_hooks(struct sighook **hook) {
+	struct sighook *next = sighook(SIGALRM, alrm_hook, NULL, SH_CONTINUE);
+	if (!bfs_pcheck(next, "sighook(SIGALRM)")) {
+		return -1;
+	}
+
+	sigunhook(*hook);
+	*hook = next;
+	return 0;
+}
+
+/** Background thread that rapidly (un)registers signal hooks. */
+static void *hook_thread(void *ptr) {
+	struct sighook *hook = sighook(SIGALRM, alrm_hook, NULL, SH_CONTINUE);
+	if (!bfs_pcheck(hook, "sighook(SIGALRM)")) {
+		return NULL;
+	}
+
+	while (load(&count, relaxed) < 1000) {
+		if (swap_hooks(&hook) != 0) {
+			sigunhook(hook);
+			return NULL;
+		}
+	}
+
+	sigunhook(hook);
+	return &count;
+}
+
+bool check_sighook(void) {
+	bool ret = true;
+
+	struct sighook *hook = sighook(SIGALRM, alrm_hook, NULL, SH_CONTINUE);
+	ret &= bfs_pcheck(hook, "sighook(SIGALRM)");
+	if (!ret) {
+		goto done;
+	}
+
+	struct itimerval ival = {
+		.it_value = {
+			.tv_usec = 100,
+		},
+		.it_interval = {
+			.tv_usec = 100,
+		},
+	};
+	ret &= bfs_pcheck(setitimer(ITIMER_REAL, &ival, NULL) == 0);
+	if (!ret) {
+		goto unhook;
+	}
+
+	pthread_t thread;
+	ret &= bfs_pcheck(thread_create(&thread, NULL, hook_thread, NULL) == 0);
+	if (!ret) {
+		goto untime;
+	}
+
+	while (ret && load(&count, relaxed) < 1000) {
+		ret &= swap_hooks(&hook) == 0;
+	}
+
+ 	void *ptr;
+	thread_join(thread, &ptr);
+	ret &= bfs_check(ptr);
+
+untime:
+	ival.it_value.tv_usec = 0;
+	ret &= bfs_pcheck(setitimer(ITIMER_REAL, &ival, NULL) == 0);
+	if (!ret) {
+		goto unhook;
+	}
+
+unhook:
+	sigunhook(hook);
+done:
+	return ret;
+}
-- 
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