[WIP/PATCH] restart writes on EINTR

[WIP/PATCH] restart writes on EINTR

[Eric Wong]

Only compile-tested, and I gotta run out for a bit and my not
return alive.  I just noticed some EINTR errors while writing to
pipes and haven't dealt with stdio or C in ages at this point.

diff --git a/src/formats_i.c b/src/formats_i.c
index 7048040d..d4082cc5 100644
--- a/src/formats_i.c
+++ b/src/formats_i.c
@@ -129,10 +129,21 @@ int lsx_padbytes(sox_format_t * ft, size_t n)
  */
 size_t lsx_writebuf(sox_format_t * ft, void const * buf, size_t len)
 {
-  size_t ret = fwrite(buf, (size_t) 1, len, (FILE*)ft->fp);
-  if (ret != len) {
-    lsx_fail_errno(ft, errno, "error writing output file");
-    clearerr((FILE*)ft->fp); /* Allows us to seek back to write header */
+  FILE *fp = (FILE*)ft->fp;
+  const char *c = (const char *)buf;
+  size_t ret = fwrite(c, 1, len, fp);
+
+  while (ret != len) {
+    switch (errno) {
+    case EINTR:
+      len -= ret;
+      c += ret;
+      ret = fwrite(c, 1, len, fp);
+      break;
+    default:
+      lsx_fail_errno(ft, errno, "error writing output file");
+      clearerr(fp); /* Allows us to seek back to write header */
+    }
   }
   ft->tell_off += ret;
   return ret;


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Re: [WIP/PATCH] restart writes on EINTR

[Måns Rullgård]

Eric Wong <normalperson@yhbt.net> writes:

> Only compile-tested, and I gotta run out for a bit and my not
> return alive.  I just noticed some EINTR errors while writing to
> pipes and haven't dealt with stdio or C in ages at this point.
>
> diff --git a/src/formats_i.c b/src/formats_i.c
> index 7048040d..d4082cc5 100644
> --- a/src/formats_i.c
> +++ b/src/formats_i.c
> @@ -129,10 +129,21 @@ int lsx_padbytes(sox_format_t * ft, size_t n)
>   */
>  size_t lsx_writebuf(sox_format_t * ft, void const * buf, size_t len)
>  {
> -  size_t ret = fwrite(buf, (size_t) 1, len, (FILE*)ft->fp);
> -  if (ret != len) {
> -    lsx_fail_errno(ft, errno, "error writing output file");
> -    clearerr((FILE*)ft->fp); /* Allows us to seek back to write header */
> +  FILE *fp = (FILE*)ft->fp;
> +  const char *c = (const char *)buf;
> +  size_t ret = fwrite(c, 1, len, fp);
> +
> +  while (ret != len) {
> +    switch (errno) {
> +    case EINTR:
> +      len -= ret;
> +      c += ret;
> +      ret = fwrite(c, 1, len, fp);
> +      break;
> +    default:
> +      lsx_fail_errno(ft, errno, "error writing output file");
> +      clearerr(fp); /* Allows us to seek back to write header */
> +    }
>    }
>    ft->tell_off += ret;
>    return ret;

The return value and ft->tell_off will be wrong in case the fwrite() was
restarted.

What did you do that caused the EINTR error?

-- 
Måns Rullgård


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Re: [WIP/PATCH] restart writes on EINTR

[Eric Wong]

Måns Rullgård <mans@mansr.com> wrote:
> The return value and ft->tell_off will be wrong in case the fwrite() was
> restarted.

Right, updated patch (covers fread + fflush) below; but still
somewhere else is hitting EINTR...  I'm still alive for now,
but not feeling great about it :<

> What did you do that caused the EINTR error?

SIGWINCH

-------8<-------
Subject: [PATCH] WIP EINTR handling

Still incomplete, SIGWINCH in a complex pipeline
(sox -M "|sox ..." "|sox ..." -p) is still causing problems for me
even with this patch.   Not sure how much time I can devote to
tracking more of it down of if I'll just setsid the parent script
and call it a day since I fear this can turn into a long-term
whack-a-mole situation...
---
 src/formats.c   |  6 ++++-
 src/formats_i.c | 59 +++++++++++++++++++++++++++++++++++++++----------
 2 files changed, 52 insertions(+), 13 deletions(-)

diff --git a/src/formats.c b/src/formats.c
index 3fcf4382..31ab99f8 100644
--- a/src/formats.c
+++ b/src/formats.c
@@ -370,6 +370,10 @@ static sox_bool is_url(char const * text) /* detects only wget-supported URLs */
 
 static int xfclose(FILE * file, lsx_io_type io_type)
 {
+  int ret;
+  do {
+    ret = fflush(file);
+  } while (ret == EOF && errno == EINTR);
   return
 #ifdef HAVE_POPEN
     io_type != lsx_io_file? pclose(file) :
@@ -1064,7 +1068,7 @@ int sox_close(sox_format_t * ft)
   if (ft->fp == stdin) {
     sox_globals.stdin_in_use_by = NULL;
   } else if (ft->fp == stdout) {
-    fflush(stdout);
+    lsx_flush(ft);
     sox_globals.stdout_in_use_by = NULL;
   } else if (ft->fp) {
     xfclose(ft->fp, ft->io_type);
diff --git a/src/formats_i.c b/src/formats_i.c
index 7048040d..c4ead348 100644
--- a/src/formats_i.c
+++ b/src/formats_i.c
@@ -95,11 +95,24 @@ int lsx_check_read_params(sox_format_t * ft, unsigned channels,
  */
 size_t lsx_readbuf(sox_format_t * ft, void *buf, size_t len)
 {
-  size_t ret = fread(buf, (size_t) 1, len, (FILE*)ft->fp);
-  if (ret != len && ferror((FILE*)ft->fp))
-    lsx_fail_errno(ft, errno, "lsx_readbuf");
-  ft->tell_off += ret;
-  return ret;
+  FILE *fp = (FILE*)ft->fp;
+
+  while (1) {
+    size_t ret = fread(buf, 1, len, fp);
+    ft->tell_off += ret;
+
+    if (ret)
+      return ret;
+
+    if (feof(fp))
+      break;
+    if (ferror(fp) && errno != EINTR) {
+      lsx_fail_errno(ft, errno, "lsx_readbuf");
+      break;
+    }
+  }
+
+  return 0;
 }
 
 /* Skip input without seeking. */
@@ -129,13 +142,29 @@ int lsx_padbytes(sox_format_t * ft, size_t n)
  */
 size_t lsx_writebuf(sox_format_t * ft, void const * buf, size_t len)
 {
-  size_t ret = fwrite(buf, (size_t) 1, len, (FILE*)ft->fp);
-  if (ret != len) {
-    lsx_fail_errno(ft, errno, "error writing output file");
-    clearerr((FILE*)ft->fp); /* Allows us to seek back to write header */
+  FILE *fp = (FILE*)ft->fp;
+  const char *c = (const char *)buf;
+  sox_uint64_t orig_off = ft->tell_off;
+
+  while (len) {
+    size_t ret = fwrite(c, 1, len, fp);
+
+    ft->tell_off += ret;
+    c += ret;
+    len -= ret;
+    if (len && ferror(fp)) {
+      if (errno == EINTR) {
+        clearerr(fp);
+        /* retry */
+      } else {
+        lsx_fail_errno(ft, errno, "error writing output file");
+        clearerr(fp); /* Allows us to seek back to write header */
+        break;
+      }
+    }
   }
-  ft->tell_off += ret;
-  return ret;
+
+  return ft->tell_off - orig_off;
 }
 
 sox_uint64_t lsx_filelength(sox_format_t * ft)
@@ -148,7 +177,13 @@ sox_uint64_t lsx_filelength(sox_format_t * ft)
 
 int lsx_flush(sox_format_t * ft)
 {
-  return fflush((FILE*)ft->fp);
+  int ret;
+
+  do {
+    ret = fflush((FILE *)ft->fp);
+  } while (ret == EOF && errno == EINTR);
+
+  return ret;
 }
 
 off_t lsx_tell(sox_format_t * ft)


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