ЭЛЕКТРОННАЯ БИБЛИОТЕКА КОАПП |
Сборники Художественной, Технической, Справочной, Английской, Нормативной, Исторической, и др. литературы. |
11.13. Storing Data Structures to DiskProblemYou want to save your large, complex data structure to disk so you don't have to build it up each time your program runs. SolutionUse the CPAN module Storable's use Storable; store(\%hash, "filename"); # later on... $href = retrieve("filename"); # by ref %hash = %{ retrieve("filename") }; # direct to hash DiscussionThe Storable module uses C functions and a binary format to walk Perl's internal data structures and lay out its data. It's more efficient than a pure Perl and string-based approach, but it's also more fragile.
use Storable qw(nstore); nstore(\%hash, "filename"); # later ... $href = retrieve("filename"); No matter whether The Here's code to save a hash to a file, with locking. We don't open with the use Storable qw(nstore_fd); use Fcntl qw(:DEFAULT :flock); sysopen(DF, "/tmp/datafile", O_RDWR|O_CREAT, 0666) or die "can't open /tmp/datafile: $!"; flock(DF, LOCK_EX) or die "can't lock /tmp/datafile: $!"; nstore_fd(\%hash, *DF) or die "can't store hash\n"; truncate(DF, tell(DF)); close(DF); Here's code to restore that hash from a file, with locking: use Storable; use Fcntl qw(:DEFAULT :flock); open(DF, "< /tmp/datafile") or die "can't open /tmp/datafile: $!"; flock(DF, LOCK_SH) or die "can't lock /tmp/datafile: $!"; $href = retrieve(*DF); close(DF); With care, you can pass large data objects efficiently between processes with this strategy, since a filehandle connected to a pipe or socket is still a byte stream, just like a plain file. Unlike the various DBM bindings, Storable does not restrict you to using only hashes (or arrays, with DB_File). Arbitrary data structures, including objects, can be stored to disk. The whole structure must be read in or written out in its entirety. See AlsoThe section on "Remote Procedure Calls (RPC)" in Chapter 13 of Advanced Perl Programming; Recipe 11.14 |