подождите, пока дочерний процесс остановится или завершится (wait for a child process to stop or terminate)
Возвращаемое значение (Return value)
If wait() or waitpid() returns because the status of a child
process is available, these functions shall return a value equal
to the process ID of the child process for which status is
reported. If wait() or waitpid() returns due to the delivery of a
signal to the calling process, -1 shall be returned and errno set
to [EINTR]. If waitpid() was invoked with WNOHANG set in
options, it has at least one child process specified by pid for
which status is not available, and status is not available for
any process specified by pid, 0 is returned. Otherwise, -1 shall
be returned, and errno set to indicate the error.
