atomic_write.h File Reference

#include <cstddef>
#include <filesystem>

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Functions
void	write_bytes_atomic (const std::filesystem::path &target, const void *bytes, std::size_t size, bool restrict_perms=false)

Function Documentation

write_bytes_atomic()

void write_bytes_atomic	(	const std::filesystem::path &	target,
		const void *	bytes,
		std::size_t	size,
		bool	restrict_perms = false
	)

Atomically write size bytes from bytes to target.

Writes to a sibling <target>.tmp.<process-salt>.<seq> first, then std::filesystem::renames onto the target. The rename is atomic on POSIX same-filesystem and on Win32 (replace-existing semantics), so concurrent writers in different processes / threads either see the previous complete file or one complete writer's payload — never a partial-write file on the visible path.

The temp-path suffix combines a process-unique 64-bit salt (drawn once per process from std::random_device) with a process-local atomic counter, so concurrent writers never collide on their intermediates.

When restrict_perms is true, the temp file is chmod'd to owner-only (0600) before the rename, so the post-rename file inherits the tight permissions without a brief world-readable window. No-op on Windows where the POSIX permission model doesn't apply.

Throws std::runtime_error on open/write/rename failure; the temp file is unlinked before throwing. Assumes target.parent_path() already exists.

Definition at line 132 of file CPfilepaths.cpp.