h5testFileLocking {rhdf5} | R Documentation

## Test and set file locking for HDF5

### Description

HDF5 1.10 uses file locking by default. On some file systems this is not available, and the HDF5 library will throw an error if the user attempts to create or access a file located on such a file system. These functions help identify if file locking is available without throwing an error, and allow the locking to be disabled for the duration of the R session if needed.

### Usage

    h5testFileLocking(location)
    h5disableFileLocking()
    h5enableFileLocking()

### Arguments

`location` | The name of a directory or file to test. If an existing directory is provided a temporary file will be created in this folder. If non-existant location is provided a file with the name will be created, tested for file locking, and then removed. Providing an existing file will result in an error.

### Details

`h5testFileLocking` will create a temporary file and then attempt to apply a file lock using the appropriate function within the HDF5 library. The success or failure of the locking is then recorded and the temporary file removed. Even relatively low level functions such as `H5Fcreate` will fail inelegantly if file locking fails.

`h5disableFileLocking` will set the environment variable `RHDF5_USE_FILE_LOCKING=FALSE`, which is the recommended was to disable this behaviour if file locking is not supported. This will only persist within the current R session. You can set the environment variable outside of R if this is a more general issue on your system.

`h5enableFileLocking` will unset the `RHDF5_USE_FILE_LOCKING`.

More discussion of HDF5's use of file locking can be found online e.g. https://forum.hdfgroup.org/t/hdf5-1-10-0-and-flock/3761/4 or https://forum.hdfgroup.org/t/hdf5-files-on-nfs/3985/5

### Value

`h5testFileLocking` returns `TRUE` if a file can be successfully locked at the specified location, or `FALSE` otherwise.

`h5disableFileLocking` and `h5enableFileLocking` set are called for the side effect of setting or unsetting the environment variable `HDF5_USE_FILE_LOCKING` and do not return anything.

### Author(s)

Mike Smith

### Examples

    ## either a file name or directory can be tested
    file <- tempfile()
    dir <- tempdir()

    h5testFileLocking(dir)
    h5testFileLocking(file)

    ## we can check for file locking, and disable if needed
    if( !h5testFileLocking(dir) ) {
      h5disableFileLocking()
    }

[Package rhdf5 version 2.34.0 Index]