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Bug #703

closed

string output duplication occurs if the same file descriptor written to in different threads

Added by rogerdpack (Roger Pack) over 12 years ago. Updated about 10 years ago.

Status:
Closed
Priority:
Normal
Assignee:
-
Target version:
-
ruby -v:
Backport:
[ruby-core:19668]

Description

=begin
ruby-dev:32566

a = Thread.new { p '4'}
b = Thread.new { p '3' }
a.join
b.join

results in
"4"
"3"
"4"
"3"

because the buffer is modified simultaneously by two threads within io_fflush [I think].
=end

Actions #1

Updated by gnufied (hemant kumar) over 12 years ago

=begin
I do not see this problem, with:

ruby 1.9.0 (2008-09-30 revision 0) [i686-linux]

=end

Actions #2

Updated by matz (Yukihiro Matsumoto) over 12 years ago

=begin
Hi,

In message "Re: [ruby-core:19668] [Bug #703] string output duplication occurs if the same file descriptor written to in different threads"
on Sat, 1 Nov 2008 02:38:52 +0900, Roger Pack redmine@ruby-lang.org writes:

|ruby-dev:32566

It's not related to ruby-dev:32566, I think.

|a = Thread.new { p '4'}
|b = Thread.new { p '3' }
|a.join
|b.join
|
|results in
|"4"
|"3"
|"4"
|"3"
|
|because the buffer is modified simultaneously by two threads within io_fflush [I think].

It doesn't happen on either trunk nor 1.8.7. What's your version, and
platform?

                        matz.

=end

Actions #3

Updated by nobu (Nobuyoshi Nakada) over 12 years ago

=begin
Hi,

At Mon, 3 Nov 2008 09:04:37 +0900,
Yukihiro Matsumoto wrote in [ruby-core:19676]:

It doesn't happen on either trunk nor 1.8.7. What's your version, and
platform?

It could reproduced with full ruby, but not with miniruby nor
full ruby with disabling gems.

$ ./ruby -v bug-703.rb
ruby 1.9.0 (2008-11-03 revision 20092) [i686-linux]
"4"
"3"
"4"
"3"

$ ./ruby --disable-gems bug-703.rb
"4"
"3"

Interestingly, -v makes it occur again.

$ ./ruby -v --disable-gems bug-703.rb
ruby 1.9.0 (2008-11-03 revision 20092) [i686-linux]
"4"
"3"
"4"
"3"

But -v after --disable-gems doesn't.

$ ./ruby --disable-gems -v bug-703.rb
ruby 1.9.0 (2008-11-03 revision 20092) [i686-linux]
"4"
"3"

--
Nobu Nakada

=end

Actions #4

Updated by nobu (Nobuyoshi Nakada) over 12 years ago

=begin
Hi,

At Mon, 3 Nov 2008 09:44:44 +0900,
Nobuyoshi Nakada wrote in [ruby-core:19678]:

It doesn't happen on either trunk nor 1.8.7. What's your version, and
platform?

It could reproduced with full ruby, but not with miniruby nor
full ruby with disabling gems.

It seems a mere timing and probability issue. And seems solved
by serializing write operations, as Roger figured out.

Index: gc.c
===================================================================
--- gc.c (revision 20101)
+++ gc.c (working copy)
@@ -1509,4 +1509,5 @@ gc_mark_children(rb_objspace_t *objspace
gc_mark(objspace, obj->as.file.fptr->writeconv_pre_ecopts, lev);
gc_mark(objspace, obj->as.file.fptr->encs.ecopts, lev);

  • gc_mark(objspace, obj->as.file.fptr->write_lock, lev); } break; Index: io.c =================================================================== --- io.c (revision 20101) +++ io.c (working copy) @@ -525,9 +525,27 @@ rb_write_internal(int fd, void *buf, siz }

+static long
+io_writable_length(rb_io_t *fptr, long l)
+{

  • if (PIPE_BUF < l &&
  • !rb_thread_alone() &&
  • wsplit_p(fptr)) {
  • l = PIPE_BUF;
  • }
  • return l; +} + +static VALUE +io_flush_buffer(VALUE arg) +{
  • rb_io_t *fptr = (rb_io_t *)arg;
  • long l = io_writable_length(fptr, fptr->wbuf_len);
  • return rb_write_internal(fptr->fd, fptr->wbuf+fptr->wbuf_off, l); +} + static int io_fflush(rb_io_t *fptr) {
  • int r, l;
  • int wbuf_off, wbuf_len;
  • long r;

    rb_io_check_closed(fptr);
    @@ -540,13 +558,5 @@ io_fflush(rb_io_t *fptr)
    if (fptr->wbuf_len == 0)
    return 0;

  • wbuf_off = fptr->wbuf_off;

  • wbuf_len = fptr->wbuf_len;

  • l = wbuf_len;

  • if (PIPE_BUF < l &&

  •    !rb_thread_alone() &&
    
  •    wsplit_p(fptr)) {
    
  •    l = PIPE_BUF;
    
  • }

  • r = rb_write_internal(fptr->fd, fptr->wbuf+wbuf_off, l);

  • r = rb_mutex_synchronize(fptr->write_lock, io_flush_buffer, (VALUE)fptr);
    /* xxx: Other threads may modify wbuf.

    • A lock is required, definitely. */ @@ -732,9 +742,23 @@ make_writeconv(rb_io_t *fptr)

/* writing functions */
+struct binwrite_arg {

  • rb_io_t *fptr;
  • VALUE str;
  • long offset;
  • long length; +}; + +static VALUE +io_binwrite_string(VALUE arg) +{
  • struct binwrite_arg *p = (struct binwrite_arg *)arg;
  • long l = io_writable_length(p->fptr, p->length);
  • return rb_write_internal(p->fptr->fd, RSTRING_PTR(p->str)+p->offset, l); +}

static long
io_binwrite(VALUE str, rb_io_t *fptr, int nosync)
{

  • long len, n, r, l, offset = 0;
  • long len, n, r, offset = 0;

    len = RSTRING_LEN(str);
    @@ -745,7 +769,10 @@ io_binwrite(VALUE str, rb_io_t *fptr, in
    fptr->wbuf_capa = 8192;
    fptr->wbuf = ALLOC_N(char, fptr->wbuf_capa);

  • fptr->write_lock = rb_mutex_new();
    }
    if ((!nosync && (fptr->mode & (FMODE_SYNC|FMODE_TTY))) ||
    (fptr->wbuf && fptr->wbuf_capa <= fptr->wbuf_len + len)) {

  • struct binwrite_arg arg;
    +
    /* xxx: use writev to avoid double write if available */
    if (fptr->wbuf_len && fptr->wbuf_len+len <= fptr->wbuf_capa) {
    @@ -767,12 +794,10 @@ io_binwrite(VALUE str, rb_io_t *fptr, in
    rb_io_check_closed(fptr);
    }

  • arg.fptr = fptr;

  • arg.str = str;

  • arg.offset = offset;
    retry:

  •    l = n;
    
  •    if (PIPE_BUF < l &&
    
  •        !rb_thread_alone() &&
    
  •        wsplit_p(fptr)) {
    
  •        l = PIPE_BUF;
    
  •    }
    
  • r = rb_write_internal(fptr->fd, RSTRING_PTR(str)+offset, l);

  • arg.length = n;

  • r = rb_mutex_synchronize(fptr->write_lock, io_binwrite_string, (VALUE)&arg);
    /* xxx: other threads may modify given string. */
    if (r == n) return len;
    @@ -3040,4 +3065,17 @@ finish_writeconv(rb_io_t *fptr, int nora
    }

+struct finish_writeconv_arg {

  • rb_io_t *fptr;
  • int noraise; +}; + +static VALUE +finish_writeconv_sync(VALUE arg) +{
  • struct finish_writeconv_arg *p = (struct finish_writeconv_arg *)arg;
  • finish_writeconv(p->fptr, p->noraise);
  • return Qnil; +} + static void fptr_finalize(rb_io_t *fptr, int noraise) @@ -3045,5 +3083,13 @@ fptr_finalize(rb_io_t *fptr, int noraise int ebadf = 0; if (fptr->writeconv) {
  • finish_writeconv(fptr, noraise);
  • if (fptr->write_lock) {
  • struct finish_writeconv_arg arg;
  • arg.fptr = fptr;
  • arg.noraise = noraise;
  • rb_mutex_synchronize(fptr->write_lock, finish_writeconv_sync, (VALUE)&arg);
  • }
  • else {
  • finish_writeconv(fptr, noraise);
  • }
    }
    if (fptr->wbuf_len) {

    Index: include/ruby/io.h

    --- include/ruby/io.h (revision 20101)
    +++ include/ruby/io.h (working copy)
    @@ -74,4 +74,5 @@ typedef struct rb_io_t {
    int writeconv_initialized;

  • VALUE write_lock;
    } rb_io_t;

@@ -134,4 +135,5 @@ typedef struct rb_io_t {
fp->encs.ecflags = 0;\
fp->encs.ecopts = Qnil;\

  • fp->write_lock = 0;\ } while (0)

--
Nobu Nakada

=end

Actions #5

Updated by nobu (Nobuyoshi Nakada) over 12 years ago

  • Status changed from Open to Closed
  • % Done changed from 0 to 100

=begin
Applied in changeset r20144.
=end

Actions #6

Updated by rogerdpack (Roger Pack) over 12 years ago

=begin
Thank you that fixed it. I don't have OS X to be able to tell if the test named after ruby-dev:32566 is also fixed but wouldn't be surprised if it was.
Regards.
-=R
=end

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