Example of using package flock

#### IN ORDER ####
# In first session, run:
write(1, "test.txt")
obj.lock <- flock::lock("test.txt")

# In second session, run this (this will wait the unlock in the first session)
obj.lock <- flock::lock("test.txt")
write(2, "test.txt", append = TRUE)
flock::unlock(obj.lock)

# Then run this in first session (session 2 will run when unlocking)
write(3, "test.txt", append = TRUE)
flock::unlock(obj.lock)

# Verif in any session (3 is written before 2)
readLines("test.txt")