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Add IO#pread and IO#pwrite methods

These methods are useful for safe/concurrent file I/O in
multi-thread/process environments and also fairly standard
nowadays especially in systems supporting pthreads.

Based on patches by Avseyev <sergey.avseyev@gmail.com> at
[ruby-core:79290].  [Feature #4532]

* configure.in: check for pwrite(2).  pread() is already used
  internally for IO.copy_stream.

* io.c: implement wrappers for pread(2) and pwrite(2) and expose
  them in IO.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58240 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
This commit is contained in:
nobu 2017-04-03 00:10:50 +00:00
parent 78ad438f0a
commit 8109114b18
5 changed files with 175 additions and 0 deletions

5
NEWS
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@ -24,6 +24,11 @@ with all sufficient information, see the ChangeLog file or Redmine
* Integer.sqrt [Feature #13219]
* IO
* IO#pread [Feature #4532]
* IO#pwrite [Feature #4532]
* Regexp
* Update Onigmo 6.1.1.
* Support absent operator https://github.com/k-takata/Onigmo/issues/82

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@ -2427,6 +2427,7 @@ AC_CHECK_FUNCS(posix_fadvise)
AC_CHECK_FUNCS(posix_memalign)
AC_CHECK_FUNCS(ppoll)
AC_CHECK_FUNCS(pread)
AC_CHECK_FUNCS(pwrite)
AC_CHECK_FUNCS(qsort_r)
AC_CHECK_FUNCS(qsort_s)
AC_CHECK_FUNCS(readlink)

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@ -37,6 +37,9 @@ arton
* He is the distributor of ActiveScriptRuby and experimental 1.9.0-x installers for win32.
* Wrote patches for win32ole, gc.c, tmpdir.rb
Sergey Avseyev
* Added IO#pread and IO#pwrite.
== B
Daniel Berger

145
io.c
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@ -4832,6 +4832,148 @@ rb_io_sysread(int argc, VALUE *argv, VALUE io)
return str;
}
#if defined(HAVE_PREAD) || defined(HAVE_PWRITE)
struct prdwr_internal_arg {
int fd;
void *buf;
size_t count;
off_t offset;
};
#endif /* HAVE_PREAD || HAVE_PWRITE */
#if defined(HAVE_PREAD)
static VALUE
internal_pread_func(void *arg)
{
struct prdwr_internal_arg *p = arg;
return (VALUE)pread(p->fd, p->buf, p->count, p->offset);
}
static VALUE
pread_internal_call(VALUE arg)
{
struct prdwr_internal_arg *p = (struct prdwr_internal_arg *)arg;
return rb_thread_io_blocking_region(internal_pread_func, p, p->fd);
}
/*
* call-seq:
* ios.pread(maxlen, offset[, outbuf]) -> string
*
* Reads <i>maxlen</i> bytes from <em>ios</em> using the pread system call
* and returns them as a string without modifying the underlying
* descriptor offset. This is advantageous compared to combining IO#seek
* and IO#read in that it is atomic, allowing multiple threads/process to
* share the same IO object for reading the file at various locations.
* This bypasses any userspace buffering of the IO layer.
* If the optional <i>outbuf</i> argument is present, it must
* reference a String, which will receive the data.
* Raises <code>SystemCallError</code> on error, <code>EOFError</code>
* at end of file and <code>NotImplementedError</code> if platform does not
* implement the system call.
*
* f = File.new("testfile")
* f.read #=> "This is line one\nThis is line two\n"
* f.pread(12, 0) #=> "This is line"
* f.pread(9, 8) #=> "line one\n"
*/
static VALUE
rb_io_pread(int argc, VALUE *argv, VALUE io)
{
VALUE len, offset, str;
rb_io_t *fptr;
ssize_t n;
struct prdwr_internal_arg arg;
rb_scan_args(argc, argv, "21", &len, &offset, &str);
arg.count = NUM2SIZET(len);
arg.offset = NUM2OFFT(offset);
io_setstrbuf(&str, (long)arg.count);
if (arg.count == 0) return str;
arg.buf = RSTRING_PTR(str);
GetOpenFile(io, fptr);
rb_io_check_byte_readable(fptr);
arg.fd = fptr->fd;
rb_io_check_closed(fptr);
rb_str_locktmp(str);
n = (ssize_t)rb_ensure(pread_internal_call, (VALUE)&arg, rb_str_unlocktmp, str);
if (n == -1) {
rb_sys_fail_path(fptr->pathv);
}
io_set_read_length(str, n);
if (n == 0 && arg.count > 0) {
rb_eof_error();
}
OBJ_TAINT(str);
return str;
}
#else
# define rb_io_pread rb_f_notimplement
#endif /* HAVE_PREAD */
#if defined(HAVE_PWRITE)
static VALUE
internal_pwrite_func(void *ptr)
{
struct prdwr_internal_arg *arg = ptr;
return (VALUE)pwrite(arg->fd, arg->buf, arg->count, arg->offset);
}
/*
* call-seq:
* ios.pwrite(string, offset) -> integer
*
* Writes the given string to <em>ios</em> at <i>offset</i> using pwrite()
* system call. This is advantageous to combining IO#seek and IO#write
* in that it is atomic, allowing multiple threads/process to share the
* same IO object for reading the file at various locations.
* This bypasses any userspace buffering of the IO layer.
* Returns the number of bytes written.
* Raises <code>SystemCallError</code> on error and <code>NotImplementedError</code>
* if platform does not implement the system call.
*
* f = File.new("out", "w")
* f.pwrite("ABCDEF", 3) #=> 6
*
* File.read("out") #=> "\u0000\u0000\u0000ABCDEF"
*/
static VALUE
rb_io_pwrite(VALUE io, VALUE offset, VALUE str)
{
rb_io_t *fptr;
ssize_t n;
struct prdwr_internal_arg arg;
if (!RB_TYPE_P(str, T_STRING))
str = rb_obj_as_string(str);
arg.buf = RSTRING_PTR(str);
arg.count = (size_t)RSTRING_LEN(str);
arg.offset = NUM2OFFT(offset);
io = GetWriteIO(io);
GetOpenFile(io, fptr);
rb_io_check_writable(fptr);
arg.fd = fptr->fd;
n = (ssize_t)rb_thread_io_blocking_region(internal_pwrite_func, &arg, fptr->fd);
RB_GC_GUARD(str);
if (n == -1) rb_sys_fail_path(fptr->pathv);
return SSIZET2NUM(n);
}
#else
# define rb_io_pwrite rb_f_notimplement
#endif /* HAVE_PWRITE */
VALUE
rb_io_binmode(VALUE io)
{
@ -12464,6 +12606,9 @@ Init_IO(void)
rb_define_method(rb_cIO, "syswrite", rb_io_syswrite, 1);
rb_define_method(rb_cIO, "sysread", rb_io_sysread, -1);
rb_define_method(rb_cIO, "pread", rb_io_pread, -1);
rb_define_method(rb_cIO, "pwrite", rb_io_pwrite, 2);
rb_define_method(rb_cIO, "fileno", rb_io_fileno, 0);
rb_define_alias(rb_cIO, "to_i", "fileno");
rb_define_method(rb_cIO, "to_io", rb_io_to_io, 0);

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@ -3525,5 +3525,26 @@ __END__
end
end
end
def test_pread
make_tempfile { |t|
open(t.path) do |f|
assert_equal("bar", f.pread(3, 4))
buf = "asdf"
assert_equal("bar", f.pread(3, 4, buf))
assert_equal("bar", buf)
assert_raise(EOFError) { f.pread(1, f.size) }
end
}
end if IO.method_defined?(:pread)
def test_pwrite
make_tempfile { |t|
open(t.path, IO::RDWR) do |f|
assert_equal(3, f.pwrite(4, "ooo"))
assert_equal("ooo", f.pread(3, 4))
end
}
end if IO.method_defined?(:pread) and IO.method_defined?(:pwrite)
end
end