Ruby

fcntl

fcntl.c

lib/fcntl/lock.rb

have_type('struct flock', %w(unistd.h fcntl.h))

static VALUE mFcntl;

static void Init_FcntlLock(void);

mFcntl = rb_define_module("Fcntl");

Init_FcntlLock();

#ifdef HAVE_TYPE_STRUCT_FLOCK

static short

fix2short(VALUE val)

{

int i = FIX2INT(val);

if (i != (short)i) {

const char *s = i > 0 ? "big" : "small";

rb_raise(rb_eRangeError, "Integer %d too %s to for `short'", i, s);

}

return (short)i;

}

static short

val2short(short fallback, VALUE klass, VALUE val)

{

switch (TYPE(val)) {

case T_NIL: return fallback;

case T_SYMBOL:

val = rb_const_get(klass, SYM2ID(val));

/* fall through */

case T_FIXNUM:

return fix2short(val);

}

rb_raise(rb_eTypeError, "must be a Symbol or Integer");

}

static struct flock *

flock_ptr(VALUE self)

{

if (RSTRING_LEN(self) < sizeof(struct flock))

rb_raise(rb_eRuntimeError, "flock buffer shortened");

rb_str_modify(self);

return (struct flock *)RSTRING_PTR(self);

}

static VALUE

lock_init(int argc, VALUE *argv, VALUE self)

{

struct flock *flock;

VALUE type, whence, start, len;

rb_str_resize(self, sizeof(struct flock));

flock = flock_ptr(self);

rb_scan_args(argc, argv, "04", &type, &whence, &start, &len);

flock->l_type = val2short(F_RDLCK, mFcntl, type);

flock->l_whence = val2short(SEEK_SET, rb_cIO, whence);

flock->l_start = NIL_P(start) ? 0 : NUM2OFFT(start);

flock->l_len = NIL_P(len) ? 0 : NUM2OFFT(len);

flock->l_pid = 0;

return self;

}

static VALUE

l_type(VALUE self)

{

return INT2NUM(flock_ptr(self)->l_type);

}

static VALUE

set_l_type(VALUE self, VALUE val)

{

flock_ptr(self)->l_type = val2short(F_RDLCK, mFcntl, val);

return val;

}

static VALUE

l_whence(VALUE self)

{

return INT2NUM(flock_ptr(self)->l_whence);

}

static VALUE

set_l_whence(VALUE self, VALUE val)

{

flock_ptr(self)->l_whence = val2short(SEEK_SET, rb_cIO, val);

return val;

}

static VALUE

l_start(VALUE self)

{

return OFFT2NUM(flock_ptr(self)->l_start);

}

static VALUE

set_l_start(VALUE self, VALUE val)

{

flock_ptr(self)->l_start = NUM2OFFT(val);

return val;

}

static VALUE

l_len(VALUE self)

{

return OFFT2NUM(flock_ptr(self)->l_len);

}

static VALUE

set_l_len(VALUE self, VALUE val)

{

flock_ptr(self)->l_len = NUM2OFFT(val);

return val;

}

static VALUE

l_pid(VALUE self)

{

return PIDT2NUM(flock_ptr(self)->l_pid);

}

static VALUE

lock_inspect(VALUE self)

{

struct flock *flock = flock_ptr(self);

const char fmt[] = "#<%s: type=%s, whence=%s, start=%lld, len=%lld, pid=%ld>";

const char *name = rb_obj_classname(self);

const char *type, *whence;

switch (flock->l_type) {

case F_RDLCK: type = "F_RDLCK"; break;

case F_WRLCK: type = "F_WRLCK"; break;

case F_UNLCK: type = "F_UNLCK"; break;

default: type = "(unknown)";

}

switch (flock->l_whence) {

case SEEK_SET: whence = "SEEK_SET"; break;

case SEEK_CUR: whence = "SEEK_CUR"; break;

case SEEK_END: whence = "SEEK_END"; break;

default: whence = "(unknown)";

}

return rb_sprintf(fmt, name, type, whence,

(long long)flock->l_start,

(long long)flock->l_len,

(long)flock->l_pid);

}

static void

Init_FcntlLock(void)

{

VALUE cFcntlLock = rb_define_class_under(mFcntl, "Lock", rb_cString);

rb_define_private_method(cFcntlLock, "initialize", lock_init, -1);

rb_define_method(cFcntlLock, "type", l_type, 0);

rb_define_method(cFcntlLock, "type=", set_l_type, 1);

rb_define_method(cFcntlLock, "whence", l_whence, 0);

rb_define_method(cFcntlLock, "whence=", set_l_whence, 1);

rb_define_method(cFcntlLock, "start", l_start, 0);

rb_define_method(cFcntlLock, "start=", set_l_start, 1);

rb_define_method(cFcntlLock, "len", l_len, 0);

rb_define_method(cFcntlLock, "len=", set_l_len, 1);

rb_define_method(cFcntlLock, "pid", l_pid, 0);

rb_define_method(cFcntlLock, "inspect", lock_inspect, 0);

rb_require("fcntl/lock");

}

#else /* ! HAVE_TYPE_STRUCT_FLOCK */

static void Init_FcntlLock(void) { }

#endif /* HAVE_TYPE_STRUCT_FLOCK */

# Fcntl::Lock is used for POSIX advisory record locks. Unlike File#flock,

# POSIX locks provide byte-range granularity and work with some

# implementations of NFS.

#

# Fcntl::Lock objects may be passed as the second argument to IO#fcntl,

# but there is also a high-level interface documented in examples

# below.

#

# Fcntl::Lock objects consists of the following readable and writable

# attributes:

#

# - type - the type of lock: :F_RDLCK, :F_WRLCK, :F_UNLCK

# - whence - interpretation of +start+: :SEEK_SET, :SEEK_CUR, :SEEK_END

# - start - starting offset (in bytes)

# - len - number of bytes to lock, zero for the entire file

#

# The +pid+ attribute is read-only and used for Fcntl::Lock.get operations,

# it is the process identifier holding the lock.

#

# Examples:

#

# file = File.open("/path/to/file", "rb+")

# Fcntl::Lock.synchronize(file) do

# # other processes may not lock any part of the file for writing

# end

#

# Fcntl::Lock.synchronize(file, :F_RDLCK, :SEEK_SET, 90, 10) do

# # places a shared read lock on the 10 bytes after the first 90 bytes

# end

#

# Fcntl::Lock.get(file)

# #=> #<Fcntl::Flock: type=F_RDLCK, whence=SEEK_SET, start=90, len=10, pid=4>

#

# Example (low level):

#

# lock = Fcntl::Lock.new(:F_WRLCK, :SEEK_SET, 0, 100)

# file.fcntl(Fcntl::F_SETLKW, lock)

# # first 100 bytes are now locked for reading or writing

#

# lock.type = :F_UNLCK

# file.fcntl(Fcntl::F_SETLKW, lock)

# # first 100 bytes now may be locked by other processes

class Fcntl::Lock < String

include Fcntl

def self.__fcntl_retry(file, cmd, lock) # :nodoc:

file.fcntl cmd, lock

rescue Errno::EINTR

retry

end

# Obtains an advisory lock, runs the given block and releases the lock

# when the block completes. Returns the result of the block.

#

# +type+ is optional and may be +nil+, in which case the lock +type+ is

# determined based on the file access flags.

#

# +whence+, +start+, and +len+ are all optional and documented under

# Fcntl::Lock.

def self.synchronize(file, type=nil, whence=IO::SEEK_SET, start=0, len=0)

type ||= (file.fcntl(F_GETFL) & O_ACCMODE) == O_RDONLY ? F_RDLCK : F_WRLCK

lock = new(type, whence, start, len)

__fcntl_retry(file, F_SETLKW, lock)

begin

yield file

ensure

lock.type = F_UNLCK

__fcntl_retry(file, F_SETLKW, lock)

end

end

# Describes a type of lock we would like to place on the given +file+

# but does not place it.

#

# Returns a Fcntl::Lock object that either describes a conflicting lock

# that prevents a lock from being placed or one with its type set

# to +Fcntl::F_UNLCK+ with other fields (if specified) unchanged.

#

# +type+ is optional and may be +nil+, in which case the lock +type+ is

# determined based on the file access flags.

#

# +whence+, +start+, and +len+ are all optional and documented under

# Fcntl::Lock.

def self.get(file, type=nil, whence=IO::SEEK_SET, start=0, len=0)

type ||= (file.fcntl(F_GETFL) & O_ACCMODE) == O_RDONLY ? F_RDLCK : F_WRLCK

lock = new(type, whence, start, len)

__fcntl_retry(file, F_GETLK, lock)

lock

end

end

require "test/unit"

begin

require "fcntl"

rescue LoadError

end

require "tempfile"

class TestFcntlLock < Test::Unit::TestCase

def test_initialize_noargs

flock = Fcntl::Lock.new

assert_equal Fcntl::F_RDLCK, flock.type

assert_equal IO::SEEK_SET, flock.whence

assert_equal 0, flock.start

assert_equal 0, flock.len

end

def test_inspect

expect = "#<Fcntl::Lock: type=F_RDLCK, whence=SEEK_SET, " \

"start=0, len=0, pid=0>"

assert_equal expect, Fcntl::Lock.new.inspect

end

def test_initialize_write_lock

flock = Fcntl::Lock.new Fcntl::F_WRLCK

assert_equal Fcntl::F_WRLCK, flock.type

assert_equal IO::SEEK_SET, flock.whence

assert_equal 0, flock.start

assert_equal 0, flock.len

end

def test_accessors

flock = Fcntl::Lock.new

assert_kind_of Integer, flock.pid

flock.type = Fcntl::F_UNLCK

assert_equal Fcntl::F_UNLCK, flock.type

flock.whence = IO::SEEK_CUR

assert_equal IO::SEEK_CUR, flock.whence

flock.len = 2

assert_equal 2, flock.len

flock.start = 3

assert_equal 3, flock.start

end

def test_get_lock

lock = Fcntl::Lock.new Fcntl::F_WRLCK

pid = nil

Tempfile.open(self.class.name) do |tmp|

r, w = IO.pipe

pid = fork do

File.open(tmp.path, "wb") do |fp|

fp.fcntl Fcntl::F_SETLKW, lock

r.close

w.syswrite "."

sleep

end

end

w.close

assert_equal ".", r.read(1)

r.close

tmp.fcntl Fcntl::F_GETLK, lock

end

assert_equal pid, lock.pid

Process.kill :TERM, pid

Process.waitpid2(pid)

end

def test_synchronize

lock = Fcntl::Lock.new :F_WRLCK, :SEEK_CUR, 5, 6

tmp = Tempfile.new(self.class.name)

r, w = IO.pipe

pid = fork do

r.close

Fcntl::Lock.synchronize(tmp, :F_WRLCK, :SEEK_CUR, 5, 6) do

w.syswrite('.')

sleep

end

end

w.close

assert_equal ".", r.read(1)

tmp.fcntl Fcntl::F_GETLK, lock

r.close

Process.kill :TERM, pid

Process.waitpid2(pid)

assert_equal Fcntl::F_WRLCK, lock.type

assert_equal IO::SEEK_SET, lock.whence

assert_equal 5, lock.start

assert_equal 6, lock.len

assert_equal pid, lock.pid

tmp.close!

end

def test_get_lock

tmp = Tempfile.new(self.class.name)

r, w = IO.pipe

pid = fork do

r.close

Fcntl::Lock.synchronize(tmp) do

w.syswrite('.')

sleep

end

end

w.close

assert_equal ".", r.read(1)

lock = Fcntl::Lock.get(tmp)

r.close

Process.kill :TERM, pid

Process.waitpid2(pid)

assert_equal Fcntl::F_WRLCK, lock.type

assert_equal IO::SEEK_SET, lock.whence

assert_equal 0, lock.start

assert_equal 0, lock.len

assert_equal pid, lock.pid

tmp.close!

end

end if defined? Fcntl::Lock