Malcom,
That's great! Is strerror() thread-safe in the recent version of Solaris?
In any case, to be correct you still need to make sure that the code passed to
strerror() is a valid one. For this you need to check errno after the call to
strerror(). Please check the code snippet I sent earlier for HPUX.
-- Asokan
________________________________________
From: malcolm [malcolm.kaval...@oracle.com]
Sent: Saturday, December 13, 2014 3:13 PM
To: common-dev@hadoop.apache.org
Subject: Re: Solaris Port SOLVED!
Wiping egg off face ...
After consulting with the Solaris team (and looking at the source code
and man page) , it turns out that strerror itself on Solaris is MT-Safe
! (Just like HPUX)
So, after all this effort, all I need to do is modify terror as follows:
const char* terror(int errnum)
{
#if defined(__sun)
return strerror(errnum); // MT-Safe under Solaris
#else
if ((errnum < 0) || (errnum >= sys_nerr)) {
return "unknown error.";
}
return sys_errlist[errnum];
#endif
}
And in two other files where sys_errlist is referenced directly
(NativeIO and hdfs_http_client.c), I replaced this direct access instead
with a call to terror.
Thanks for all your help and patience,
I'll file a JIRA asap,
Cheers,
Malcolm
On 12/13/2014 05:26 PM, malcolm wrote:
> Thanks Asokan,
>
> Looked up Gcc's thread local variables, seems a bit complex though and
> quite specific to Gnu.
>
> Intialization of the static errlist array should be thread safe i.e.
> initially the array is nulled out, and afterwards if two threads write
> to the same address, then they would be writing the same string.
>
> But if we are ok with changing 5 files, not just terror, then I would
> just remove terror completely and use strerror_r (or the alternatives
> for Windows and HP_UX) in the caller code instead i.e. using your
> suggestion for a local buffer in the caller, wherever needed. The more
> I think about it, the more this seems to be the right thing to do.
>
> Cheers,
> Malcolm
>
>
> On 12/13/2014 04:38 PM, Asokan, M wrote:
>> Malcom,
>> Gcc supports thread-local variables. See
>>
>> https://gcc.gnu.org/onlinedocs/gcc-3.3.1/gcc/Thread-Local.html
>>
>> I am not sure about native compilers on Solaris, HPUX, or AIX.
>>
>> In any case, I found out that the Windows native code in Hadoop seems
>> to handle error messages properly. Here is what I found:
>>
>> $ find ~/work/hadoop/hadoop-trunk/ -name '*.c'|xargs grep
>> FormatMessage|awk -F: '{print $1}'|sort -u
>> /home/asokan/work/hadoop/hadoop-trunk/hadoop-common-project/hadoop-common/src/main/native/src/org/apache/hadoop/io/nativeio/NativeIO.c
>>
>> /home/asokan/work/hadoop/hadoop-trunk/hadoop-common-project/hadoop-common/src/main/native/src/org/apache/hadoop/security/JniBasedUnixGroupsMappingWin.c
>>
>> /home/asokan/work/hadoop/hadoop-trunk/hadoop-common-project/hadoop-common/src/main/winutils/libwinutils.c
>>
>>
>>
>> $ find ~/work/hadoop/hadoop-trunk/ -name '*.c'|xargs grep terror|awk
>> -F: '{print $1}'|sort -u
>> /home/asokan/work/hadoop/hadoop-trunk/hadoop-common-project/hadoop-common/src/main/native/src/exception.c
>>
>> /home/asokan/work/hadoop/hadoop-trunk/hadoop-common-project/hadoop-common/src/main/native/src/org/apache/hadoop/io/nativeio/SharedFileDescriptorFactory.c
>>
>> /home/asokan/work/hadoop/hadoop-trunk/hadoop-common-project/hadoop-common/src/main/native/src/org/apache/hadoop/net/unix/DomainSocket.c
>>
>> /home/asokan/work/hadoop/hadoop-trunk/hadoop-common-project/hadoop-common/src/main/native/src/org/apache/hadoop/net/unix/DomainSocketWatcher.c
>>
>> /home/asokan/work/hadoop/hadoop-trunk/hadoop-common-project/hadoop-common/src/main/native/src/org/apache/hadoop/security/JniBasedUnixGroupsMapping.c
>>
>>
>>
>> This means you need not worry about the Windows version of terror().
>> You need to change five files that contain UNIX specific native code.
>>
>> I have a question on your suggested implementation:
>>
>> How do you initialize the static errlist array in a thread-safe manner?
>>
>> ________________________________
>> Here is another thread-safe implementation that I could come up with:
>>
>> #include <string.h>
>> #include <stdlib.h>
>> #include <errno.h>
>> #include <stdio.h>
>>
>> #define MESSAGE_BUFFER_SIZE 256
>>
>> char * getSystemErrorMessage(char * buf, int buf_len, int code) {
>> #if defined(_HPUX_SOURCE)
>> char * msg;
>> errno = 0;
>> msg = strerror(code);
>> if (errno == 0) {
>> strncpy(buf, msg, buf_len-1);
>> buf[buf_len-1] = '\0';
>> } else {
>> snprintf(buf, buf_len, "%s %d",
>> "Can't get system error message for code", code);
>> }
>> #else
>> if (strerror_r(code, buf, buf_len) != 0) {
>> snprintf(buf, buf_len, "%s %d",
>> "Can't get system error message for code", code);
>> }
>> #endif
>> return buf;
>> }
>>
>> #define TERROR(code) \
>> getSystemErrorMessage(messageBuffer, sizeof(messageBuffer), code)
>>
>> int main(int argc, char ** argv) {
>> if (argc > 1) {
>> char messageBuffer[MESSAGE_BUFFER_SIZE];
>> int code = atoi(argv[1]);
>>
>> fprintf(stderr, "System error for code %s: %s\n", argv[1],
>> TERROR(code));
>> }
>> return 0;
>> }
>>
>>
>> This changes terror to a macro TERROR and requires all functions that
>> call TERROR macro to declare the local variable messageBuffer. Since
>> there are only five files to modify, I think it is not a big effort.
>> What do you think?
>>
>> -- Asokan
>>
>> On 12/13/2014 04:29 AM, malcolm wrote:
>> Colin,
>>
>> I am not sure what you mean by a thread-local buffer (in native
>> code). In Java this is pretty standard, but I couldn't find any
>> implementation for C code.
>>
>> Here is the terror function:
>>
>> const char* terror(int errnum)
>> {
>> if ((errnum < 0) || (errnum >= sys_nerr)) {
>> return "unknown error.";
>> }
>> return sys_errlist[errnum];
>> }
>>
>>
>> The interface is identical to strerror, but the implementation is
>> actually re-entrant since it returns a pointer to a static string.
>>
>> If I understand your suggestion, the new function would look like this:
>>
>> const char* terror(int errnum)
>> {
>> static char result[65];
>>
>> strerror_r(errnum, result, 64);
>>
>> return result;
>> }
>>
>> No need for snprintf, strerror_r has the 'n' bounding built-in.
>>
>> Of course, this is still non-re-entrant, so unless the caller copies
>> the returned buffer, before the function is called again, there is a
>> problem.
>>
>> After considerable thought, I have come up with this version of
>> terror, tested OK on Windows, Linux and Solaris:
>>
>> #if defined(_WIN32)
>> #define strerror_r(errno,buf,len) strerror_s(buf,len,errno)
>> #endif
>>
>> #define MAX_ERRORS 256
>> #define MAX_ERROR_LEN 80
>>
>> char *terror(int errnum)
>> {
>>
>> static char errlist[MAX_ERRORS][MAX_ERROR_LEN+1]; // cache of
>> error messages
>>
>> if ( errnum >= 0 && errnum < MAX_ERRORS )
>> {
>> if ( errlist[errnum][0] == 0 )
>> strerror_r( errnum, errlist[errnum], MAX_ERROR_LEN);
>>
>> return errlist[errnum];
>> }
>> else
>> {
>> return "Unknown error";
>> }
>> }
>>
>> This version is portable and re-entrant.
>>
>> On windows, the largest errnum is 43, on Ubuntu 14.04 we have 133,
>> and on Solaris 11.1 we get 151.
>>
>> If this is OK with you, I will open a jira for this.
>>
>>
>> Thanks,
>> Malcolm
>>
>>
>> On 12/12/2014 11:10 PM, Colin McCabe wrote:
>> Just use snprintf to copy the error message from strerror_r into a
>> thread-local buffer of 64 bytes or so. Then preserve the existing
>> terror() interface.
>>
>> Can you open a jira for this?
>>
>> best,
>> Colin
>>
>> On Thu, Dec 11, 2014 at 8:35 PM,
>> malcolm<malcolm.kaval...@oracle.com><mailto:malcolm.kaval...@oracle.com>
>> wrote:
>> So, turns out that if I had naively changed all calls to terror or
>> references to sys_errlist, to using strerror_r, then I would have broken
>> code for Windows and HPUX (and possibly other OSes).
>>
>> If we are to assume that current code runs fine on all platforms
>> (maybe even
>> AIX an MacOS, for example), then any change/additions made to the
>> code and
>> not ifdeffed appropriately can break on other OSes. On the other
>> hand, too
>> many ifdefs can pollute the code source and render it less readable
>> (though
>> possibly less important).
>>
>> In the general case what are code contributors responsibilities to
>> adding
>> code regarding OSes besides Linux ?
>> What OSes does jenkins test on ?
>> I guess maintainers of code on non-tested platforms are responsible for
>> their own testing ?
>>
>> How do we avoid the ping-pong effect, i.e. I make a generic change to
>> code
>> which breaks on Windows, then the Windows maintainer reverts changes to
>> break on Solaris for example ? Or does this not happen in actuality ?
>>
>>
>> On 12/11/2014 11:25 PM, Asokan, M wrote:
>> Hi Malcom,
>> The Windows versions of strerror() and strerror_s() functions are
>> probably meant for ANSI C library functions that set errno. For core
>> Windows API calls (like UNIX system calls), one gets the error number by
>> calling GetLastError() function. In the code snippet I sent earlier,
>> the
>> "code" argument is the value returned by GetLastError(). Neither
>> strerror()
>> nor strerror_s() will give the correct error message for this error
>> code.
>>
>> You could probably look at libwinutils.c in Hadoop source. It uses
>> FormatMessageW (which returns messages in Unicode.) My requirement
>> was to
>> return messages in current system locale.
>>
>> -- Asokan
>> ________________________________________
>> From: malcolm
>> [malcolm.kaval...@oracle.com<mailto:malcolm.kaval...@oracle.com>]
>> Sent: Thursday, December 11, 2014 4:04 PM
>> To:common-dev@hadoop.apache.org<mailto:To:common-dev@hadoop.apache.org>
>> Subject: Re: Solaris Port
>>
>> Hi Asok,
>>
>> I googled and found that windows has strerror, and strerror_s (which is
>> the strerror_r equivalent).
>> Is there a reason why you didn't use this call ?
>>
>> On 12/11/2014 06:27 PM, Asokan, M wrote:
>> Hi Malcom,
>> Recently, I had to work on a function to get system error
>> message on
>> various systems. Here is the piece of code I came up with. Hope it
>> helps.
>>
>> static void get_system_error_message(char * buf, int buf_len, int code)
>> {
>> #if defined(_WIN32)
>> LPVOID lpMsgBuf;
>> DWORD status = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
>> FORMAT_MESSAGE_FROM_SYSTEM |
>> FORMAT_MESSAGE_IGNORE_INSERTS,
>> NULL, code,
>> MAKELANGID(LANG_NEUTRAL,
>> SUBLANG_DEFAULT),
>> /* Default
>> language */
>> (LPTSTR) &lpMsgBuf, 0, NULL);
>> if (status > 0)
>> {
>> strncpy(buf, (char *)lpMsgBuf, buf_len-1);
>> buf[buf_len-1] = '\0';
>> /* Free the buffer returned by system */
>> LocalFree(lpMsgBuf);
>> }
>> else
>> {
>> _snprintf(buf, buf_len-1 , "%s %d",
>> "Can't get system error message for code", code);
>> buf[buf_len-1] = '\0';
>> }
>> #else
>> #if defined(_HPUX_SOURCE)
>> {
>> char * msg;
>> errno = 0;
>> msg = strerror(code);
>> if (errno == 0)
>> {
>> strncpy(buf, msg, buf_len-1);
>> buf[buf_len-1] = '\0';
>> }
>> else
>> {
>> snprintf(buf, buf_len, "%s %d",
>> "Can't get system error message for code", code);
>> }
>> }
>> #else
>> if (strerror_r(code, buf, buf_len) != 0)
>> {
>> snprintf(buf, buf_len, "%s %d",
>> "Can't get system error message for code", code);
>> }
>> #endif
>> #endif
>> }
>>
>> Note that HPUX does not have strerror_r() since strerror() itself is
>> thread-safe. Also Windows does not have snprintf(). The equivalent
>> function _snprintf() has a subtle difference in its interface.
>>
>> -- Asokan
>> ________________________________________
>> From: malcolm
>> [malcolm.kaval...@oracle.com<mailto:malcolm.kaval...@oracle.com>]
>> Sent: Thursday, December 11, 2014 11:02 AM
>> To:common-dev@hadoop.apache.org<mailto:To:common-dev@hadoop.apache.org>
>> Subject: Re: Solaris Port
>>
>> Fine with me, I volunteer to do this, if accepted.
>>
>> On 12/11/2014 05:48 PM, Allen Wittenauer wrote:
>> sys_errlist was removed for a reason. Creating a fake sys_errlist on
>> Solaris will mean the libhadoop.so will need to be tied a specific build
>> (kernel/include pairing) and therefore limits upward
>> mobility/compatibility.
>> That doesn’t seem like a very good idea.
>>
>> IMO, switching to strerror_r is much preferred, since other than the
>> brain-dead GNU libc version, is highly portable and should work
>> regardless
>> of the kernel or OS in place.
>>
>> On Dec 11, 2014, at 5:20 AM,
>> malcolm<malcolm.kaval...@oracle.com><mailto:malcolm.kaval...@oracle.com>
>> wrote:
>>
>> FYI, there are a couple more files that reference sys_errlist directly
>> (not just terror within exception.c) , but also hdfs_http_client.c and
>> NativeiO.c
>>
>> On 12/11/2014 07:38 AM, malcolm wrote:
>> Hi Colin,
>>
>> Exactly, as you noticed, the problem is the thread-local buffer needed
>> to return from terror.
>> Currently, terror just returns a static string from an array, this is
>> fast, simple and error-proof.
>>
>> In order to use strerror_r inside terror, would require allocating a
>> buffer inside terror and depend on the caller to free the buffer after
>> using it, or to pass a buffer to terrror (which is basically the same as
>> strerror_r, rendering terror redundant).
>> Both cases require modification outside terror itself, as far as I can
>> tell, no simple fix. Unless you have an alternative which I haven't
>> thought
>> of ?
>>
>> As far as I can tell, we have two choices:
>>
>> 1. Remove terror and replace calls with strerror_r, passing a buffer
>> from the callee.
>> Advantage: a more modern portable interface.
>> Disadvantage: All calls to terror need to be modified, though
>> all seem to be in a few files as far as I can tell.
>>
>> 2. Adding a sys_errlist array (ifdeffed for Solaris)
>> Advantage: no change to any calls to terror
>> Disadvantage: 2 additional files added to source tree (.c and
>> .h) and some minor ifdefs only used for Solaris.
>>
>> I think it is more a question of style than anything else, so I leave
>> you to make the call.
>>
>> Thanks for your patience,
>> Malcolm
>>
>>
>>
>>
>>
>> On 12/10/2014 09:54 PM, Colin McCabe wrote:
>> On Wed, Dec 10, 2014 at 2:31 AM, malcolm
>> <malcolm.kaval...@oracle.com><mailto:malcolm.kaval...@oracle.com> wrote:
>> Hi Colin,
>>
>> Thanks for the hints around JIRAs.
>>
>> You are correct errno still exists, however sys_errlist does not.
>>
>> Hadoop uses a function terror (defined in exception.c) which indexes
>> sys_errlist by errno to return the error message from the array.
>> This
>> function is called 26 times in various places (in 2.2)
>>
>> Originally, I thought to replace all calls to terror with strerror,
>> but
>> there can be issues with multi-threading (it returns a buffer which
>> can be
>> overwritten), so it seemed simpler just to recreate the sys_errlist
>> message
>> array.
>>
>> There is also a multi-threaded version strerror_r where you pass the
>> buffer
>> as a parameter, but this would necessitate changing every call to
>> terror
>> with mutiple lines of code.
>> Why don't you just use strerror_r inside terror()?
>>
>> I wrote that code originally. The reason I didn't want to use
>> strerror_r there is because GNU libc provides a non-POSIX definition
>> of strerror_r, and forcing it to use the POSIX one is a pain. But you
>> can do it. You also will require a thread-local buffer to hold the
>> return from strerror_r, since it is not guaranteed to be static
>> (although in practice it is 99% of the time-- another annoyance with
>> the API).
>>
>>
>> ________________________________
>>
>>
>>
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>
________________________________
ATTENTION: -----
The information contained in this message (including any files transmitted with
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