From 68587e2920b52ad75f0badb4d3040b574797ac9e Mon Sep 17 00:00:00 2001
From: Phil Jones <philj56@gmail.com>
Date: Tue, 25 Oct 2022 00:26:03 +0100
Subject: Disallow multiple simultaneous tofi instances.

---
 src/lock.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 src/lock.c

(limited to 'src/lock.c')

diff --git a/src/lock.c b/src/lock.c
new file mode 100644
index 0000000..133d327
--- /dev/null
+++ b/src/lock.c
@@ -0,0 +1,71 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/file.h>
+#include "log.h"
+#include "xmalloc.h"
+
+static const char *default_cache_dir = ".cache/";
+static const char *lock_filename = "tofi.lock";
+
+[[nodiscard("memory leaked")]]
+static char *get_lock_path() {
+	char *lock_name = NULL;
+	const char *runtime_path = getenv("XDG_RUNTIME_DIR");
+	if (runtime_path == NULL) {
+		runtime_path = getenv("XDG_CACHE_HOME");
+	}
+	if (runtime_path == NULL) {
+		const char *home = getenv("HOME");
+		if (home == NULL) {
+			log_error("Couldn't retrieve HOME from environment.\n");
+			return NULL;
+		}
+		size_t len = strlen(home) + 1
+			+ strlen(default_cache_dir) + 1
+			+ strlen(lock_filename) + 1;
+		lock_name = xmalloc(len);
+		snprintf(
+			lock_name,
+			len,
+			"%s/%s/%s",
+			home,
+			default_cache_dir,
+			lock_filename);
+	} else {
+		size_t len = strlen(runtime_path) + 1
+			+ strlen(lock_filename) + 1;
+		lock_name = xmalloc(len);
+		snprintf(
+			lock_name,
+			len,
+			"%s/%s",
+			runtime_path,
+			lock_filename);
+	}
+	return lock_name;
+}
+
+bool lock_check(void)
+{
+	bool ret = false;
+	char *filename = get_lock_path();
+	errno = 0;
+	int fd = open(filename, O_RDONLY | O_CREAT, S_IRUSR | S_IWUSR);
+	if (fd == -1) {
+		log_error("Failed to open lock file %s: %s.\n", filename, strerror(errno));
+	} else if (flock(fd, LOCK_EX | LOCK_NB) == -1) {
+		if (errno == EWOULDBLOCK) {
+			/*
+			 * We can't lock the file because another tofi process
+			 * already has.
+			 */
+			ret = true;
+		}
+        }
+
+	free(filename);
+	return ret;
+}
-- 
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