common background fork

repertory/librepertory/include/utils/unix/unix_utils.hpp

@@ -37,6 +37,8 @@ inline const std::array<std::string, 4U> attribute_namespaces = {
 };
 #endif
 
+[[nodiscard]] auto create_daemon(std::function<int()> main_func) -> int;
+
 [[nodiscard]] auto from_api_error(api_error err) -> int;
 
 [[nodiscard]] auto to_api_error(int err) -> api_error;

repertory/librepertory/src/utils/unix/unix_utils.cpp

@@ -23,7 +23,7 @@
 
 #include "utils/unix/unix_utils.hpp"
 
-#include "utils/error_utils.hpp"
+#include "utils/path.hpp"
 
 namespace repertory::utils {
 auto from_api_error(api_error err) -> int {
@@ -223,6 +223,53 @@ void windows_create_to_unix(const UINT32 &create_options,
     mode |= (S_IXUSR);
   }
 }
+
+auto create_daemon(std::function<int()> main_func) -> int {
+  auto pid = fork();
+  if (pid < 0) {
+    return 1;
+  }
+
+  if (pid == 0) {
+    signal(SIGCHLD, SIG_DFL);
+    if (setsid() < 0) {
+      return 1;
+    }
+
+    auto second_pid = fork();
+    if (second_pid < 0) {
+      return 1;
+    }
+
+    if (second_pid > 0) {
+      exit(0);
+    }
+
+    close(STDIN_FILENO);
+    close(STDOUT_FILENO);
+    close(STDERR_FILENO);
+
+    auto file_desc = open("/dev/null", O_RDWR);
+    if (file_desc < 0) {
+      return 1;
+    }
+
+    dup2(file_desc, STDIN_FILENO);
+    dup2(file_desc, STDOUT_FILENO);
+    dup2(file_desc, STDERR_FILENO);
+
+    if (file_desc > STDERR_FILENO) {
+      close(file_desc);
+    }
+
+    umask(0);
+    chdir("/");
+    return main_func();
+  }
+
+  signal(SIGCHLD, SIG_IGN);
+  return 0;
+}
 } // namespace repertory::utils
 
-#endif // !_WIN32
+#endif // !defined(_WIN32)