Prepare to access a file by many concurrent processes:

Protect concurrent access with a lock file in the same directory:

Use several parallel processes to try to write to the same file concurrently:

The data has been written (in a nondeterministic order) without interference among the processes:

Initialize a file by writing 0 into it:

Concurrently read the file and write an updated value:

All accesses have effectively been serialized:

Unprotected concurrent accesses may overwrite each other's values and even read partial content:

Using a shared variable in WithLock is equivalent to CriticalSection:

Update operations on local symbols are automatically protected from concurrency:

If a file used as a lock already exists, the locking will hang:

This evaluation will not return until it is aborted:

Always use a nonexisting file as a lock:

If a local symbol used as a lock has a value, the locking will hang:

This evaluation will not return until it is aborted:

Always use a nonexisting local symbol as a lock:

Not all file systems support the required operation for local symbol locking:

File locks are supported in more cases:

Launch parallel kernels on the local and one remote machine:

Files and lock files created on a local file system may not be available on remote machines:

Concurrently write to file on all parallel subkernels:

Only the results from the local kernels are available in the file:

The results from the remote machine have been written to a file local to that machine:

Use a file and lock file on a shared file system:

Concurrently write to file on all parallel subkernels:

Now, all results are written to the same file: