Daniel Stenberg wrote:
On Thu, 12 Mar 2009, Hendrik Schober wrote:
The new code is attached. (Note: This doesn't crash every time I start it.
Percentage varies widely. I suppose this is an MT issue.)
MT as in multi-threading? Then nope, as the example doesn't use threads...
It does. Internally, libcurl creates a bunch of threads for the
requests. One of them crashes.
I have checked the code on a Linux machine. But that had libcurl 7.18.2
installed. I was unable to reproduce the issue on that machine.
Just now I ran it quite a number of times on 7.19.4 on linux with valgrind and
it worked fine every time! I don't have any windows box around to try on. I'm
a bit surprised too, since the example is portable and the difference between
linux and windows internally for this kind of stuff is not that big.
When 7.19.4 crashes on windows, is the stack trace the same every time? Does
it crash doing the same transfer? Does the code require 10 handles to get the
crash or can it happen with less? If so, where is the limit exactly?
The stack trace is the very same, every time:
libcurld.dll!Curl_llist_insert_next(curl_llist * list=0x01398910, curl_llist_element * e=0x035c8fe0, const void * p=0x036c1098)
Line 70 C
libcurld.dll!Curl_hash_add(curl_hash * h=0x01398810, void * key=0x03530e88, unsigned int key_len=20, void * p=0x0363d118) Line
162 + 0x14 bytes C
libcurld.dll!Curl_cache_addr(SessionHandle * data=0x0154fbd8, Curl_addrinfo * addr=0x0356a5a8, const char * hostname=0x0356aec8,
int port=80) Line 368 + 0x1a bytes C
libcurld.dll!addrinfo_callback(void * arg=0x0348c0d0, int status=0, void *
addr=0x01359490) Line 118 + 0x21 bytes C
libcurld.dll!Curl_addrinfo4_callback(void * arg=0x0348c0d0, int status=0,
hostent * hostent=0x01359490) Line 154 + 0x11 bytes C
libcurld.dll!gethostbyname_thread(void * arg=0x0348c0d0) Line 264 + 0xf
bytes C
msvcr90d.dll!_callthreadstartex() Line 348 + 0xf bytes C
msvcr90d.dll!_threadstartex(void * ptd=0x0348c6b0) Line 331 C
The real code tests with seven handles to very different URLs. I
put in those in the test so that I can quickly create as many
valid requests as I want. AFAICS, it crashes in different handles.
(At least, the URLs are different. Since those are created the
same way in a loop every time, I just assume that the handles are
different.)
With the current test, 10 handles are enough to get a crash in
about 4-8 out of 10 times I start the application. But it's not a
hard number, it's just probabilities. I've seen it working with
10,000 handles and crash with just 2.
I have the feeling that, whenever I looked closer at the crashes,
it crashed within the first ten handles, but I only have looked
closely at a few of them, so that could be accidental.
Since it always crashes in one of the threads libcurl creates
internally, and since the crashes are so unpredictable, I assume
it's a threading issue.
Do you know of any libcurl version that worked with this?
So far, I have only upgraded from 7.19.3 to the latest version
7.19.4. We had assumed the error is on our side, so I have spent
my time mainly into boiling it down into a small self-containing
repro case.
What Windows version are you testing this on?
This is XP SP3, latest patches installed. It also crashes on our
two Windows test machines.
Schobi
