#include <filelock.h>

Guard to create a file lock.

This can be used to make sure concurrent processes do not interfere when for example writing files.

The lock file will be deleted when the FileLock is destroyed.

Internally this uses some POSIX system calls to atomically check for the existence of a file and create it if it does not exists. This works even over NFS (for at least NFSv3 and Linux 2.6).

Definition at line 30 of file filelock.h.

Public Member Functions
	FileLock (const std::filesystem::path &path)
	Construct a file lock guard with a lock file at the given path. More...

	~FileLock ()
	Delete the lock file when the guard is destroyed. More...

bool	acquire ()
	Try to acquire the file lock. More...

Private Attributes
std::filesystem::path	path_
	Path to the file lock. More...

bool	acquired_
	Whether the lock has been acquired. More...

Constructor & Destructor Documentation

◆ FileLock()

smash::FileLock::FileLock ( const std::filesystem::path & path )

explicit

Construct a file lock guard with a lock file at the given path.

This will not create a file, use acquire() for that.

Parameters

[in] path Path to file.

Returns: Constructed object.

Definition at line 19 of file filelock.cc.

20 : path_(path), acquired_(false) {}

smash::FileLock::acquired_

bool acquired_

Whether the lock has been acquired.

Definition: filelock.h:56

smash::FileLock::path_

std::filesystem::path path_

Path to the file lock.

Definition: filelock.h:54

◆ ~FileLock()

smash::FileLock::~FileLock ( )

Delete the lock file when the guard is destroyed.

Definition at line 41 of file filelock.cc.

                     {
   if (acquired_) {
     std::filesystem::remove(path_);
   }
 }

Member Function Documentation

◆ acquire()

bool smash::FileLock::acquire ( )

Try to acquire the file lock.

Returns: Returns false if the file already exists. Returns true and creates the file otherwise.

Exceptions

std::runtime_error if called another time after returning true or if the lockfile cannot be closed.

Definition at line 22 of file filelock.cc.

                        {
   if (acquired_) {
     throw std::runtime_error("FileLock \"" + path_.native() +
                              "\" was already acquired.");
   }
   // The following POSIX syscall fails if the file already exists and creates it
   // otherwise. This is atomic, so there cannot be a race.
   const int fd =
       open(path_.native().c_str(), O_EXCL | O_CREAT, S_IRUSR | S_IWUSR);
   if (fd < 0) {
     return false;
   }
   acquired_ = true;
   if (close(fd) != 0) {
     throw std::runtime_error("Could not close file lock.");
   }
   return true;
 }

Member Data Documentation

◆ path_

std::filesystem::path smash::FileLock::path_

private

Path to the file lock.

Definition at line 54 of file filelock.h.

◆ acquired_

bool smash::FileLock::acquired_