<div dir="ltr">I'm somewhat concerned about following scenario:<div><br></div><div>File file_obj(...);</div><div><span style="font-size:12.8000001907349px">LockFile lock (</span>file_obj<span style="font-size:12.8000001907349px">.GetDescriptor ());</span><br></div><div><span style="font-size:12.8000001907349px">..</span></div><div><span style="font-size:12.8000001907349px"><br></span></div><div><span style="font-size:12.8000001907349px">My understanding, that on Windows if </span><span style="font-size:12.8000001907349px">LockFile duplicates original handle (i.e. </span><span style="font-size:12.8000001907349px">file.GetDescriptor ()</span><span style="font-size:12.8000001907349px">) only a duplicated handle will be allowed to call IO functions on this file within locked region, meanwhile </span>file_obj will be blocked on IO.</div><div>If <span style="font-size:12.8000001907349px">LockFile just holds a reference to original handle then </span>file_obj can proceed on IO operations in exclusive mode.<span style="font-size:12.8000001907349px"> </span></div><div><br></div><div><span style="font-size:12.8000001907349px">In order to make it clear that </span><span style="font-size:12.8000001907349px">LockFile references File we can make LockFile to take File& as constructor parameter instead of a raw handle.</span></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, May 21, 2015 at 10:28 AM, Zachary Turner <span dir="ltr"><<a href="mailto:zturner@google.com" target="_blank">zturner@google.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Why does someone other than the LockFile object care about holding a raw handle? Shouldn't it just hold a reference/pointer to the LockFile? <br><div class="HOEnZb"><div class="h5"><div class="gmail_quote">On Thu, May 21, 2015 at 10:06 AM Oleksiy Vyalov <<a href="mailto:ovyalov@google.com" target="_blank">ovyalov@google.com</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Windows file lock is tied to a file handle - using handle duplication effectively applies locking on duplicated handle, not on original, so your original handle will be blocked on IO trying to read/write.<div>Maybe we can just eliminate CloseHandle call (<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_llvm-2Dmirror_lldb_blob_master_source_Host_windows_LockFileWindows.cpp-23L50&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=DDUMf06MYELAe1Nlv7KChiwJLLHbYha4jtK_AOiWqwQ&m=AnU0fRg8cEkrU4FRRo8LBOO2c2os9lsqazJJPhM9lPA&s=M7jxj1eQtT3HJVHCjs0IZj-PuIj3evpSXZgOGtA-H5g&e=" target="_blank">https://github.com/llvm-mirror/lldb/blob/master/source/Host/windows/LockFileWindows.cpp#L50</a>) if file will be eventually closed by LockFileWindows caller.</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, May 21, 2015 at 9:58 AM, Zachary Turner <span dir="ltr"><<a href="mailto:zturner@google.com" target="_blank">zturner@google.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">I don't experience this crash but looking at the proposed fix it certainly seems like a plausible explanation. Seems to me like something should transfer ownership though rather than duplicating the handle<div><div><br><div class="gmail_quote">On Thu, May 21, 2015 at 9:52 AM Colin Riley <<a href="mailto:colin@codeplay.com" target="_blank">colin@codeplay.com</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
Windows 7 64, Debug, latest vs13.</div><div bgcolor="#FFFFFF" text="#000000"><br>
<br>
<div>On 21/05/2015 17:39, Oleksiy Vyalov
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hi Colin,
<div><br>
</div>
<div>could you give more context about crash - what build
configuration do you use (debug, release,..) and which OS?</div>
<div>I'm running this code on Windows 7 and haven't noticed any
failures.</div>
<div><br>
</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, May 21, 2015 at 8:57 AM, Colin
Riley <span dir="ltr"><<a href="mailto:colin@codeplay.com" target="_blank">colin@codeplay.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"> <br>
Zachary, do you see this on windows at all? Tip for us
results in crashes when releasing file descriptors without
the below fix. <br>
<br>
Colin
<div>
<div><br>
<br>
<div>On 19/05/2015 12:52, Aidan Dodds wrote:<br>
</div>
</div>
</div>
<blockquote type="cite">
<div>
<div>Hi, <br>
<br>
We have been seeing a crash on windows when
connecting to an android target using lldb-server. <br>
I am not sure if this affects other platforms too. <br>
I think this was introduced with <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_D9056&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=DDUMf06MYELAe1Nlv7KChiwJLLHbYha4jtK_AOiWqwQ&m=AnU0fRg8cEkrU4FRRo8LBOO2c2os9lsqazJJPhM9lPA&s=yXsPcdmH0YtsyvNtFMke9wMIdBYbAN2f8YGnxcYfLbM&e=" target="_blank">http://reviews.llvm.org/D9056</a>.
<br>
<br>
I tracked the crash back to the workings of
ModuleCache::GetAndPut(). <br>
<br>
The crash seems to be due to a file descriptor being
released twice, once by the original "File
lock_file" and again by the "LockFile lock" who
share the same file descriptor. <br>
<br>
The file descriptor sharing happens because of this
line: <br>
ModuleCache.cpp @ 164 <br>
LockFile lock (lock_file.GetDescriptor ()); <br>
<br>
Both destructors attempt to release effectively the
same file descriptor. I was able to fix the crash
by duplicating the file handle in the lock file
constructor using _dup(). (patch attached) <br>
I wasn't sure if this was the right fix however. Has
anyone else seen this? <br>
Should "File lock_file" perhaps transfer its file
descriptor completely rather then share it? <br>
<br>
Thanks, <br>
Aidan <br>
<br>
<fieldset></fieldset>
<br>
</div>
</div>
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<div>
<div dir="ltr"><span style="color:rgb(85,85,85);font-family:sans-serif;line-height:20px;background-color:rgb(255,255,255);border-width:2px 0px 0px;border-style:solid;border-color:rgb(213,15,37);padding-top:2px;margin-top:2px">Oleksiy
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<pre cols="72">--
- Colin Riley
Senior Director,
Parallel/Graphics Debugger Systems
Codeplay Software Ltd
45 York Place, Edinburgh, EH1 3HP
Tel: 0131 466 0503
Fax: 0131 557 6600
Website: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__www.codeplay.com&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=DDUMf06MYELAe1Nlv7KChiwJLLHbYha4jtK_AOiWqwQ&m=AnU0fRg8cEkrU4FRRo8LBOO2c2os9lsqazJJPhM9lPA&s=fyw3nMZirw-az_D3WoYlO7a93TrBtjGVMN6tIPXTnUg&e=" target="_blank">http://www.codeplay.com</a>
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</div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br><div><div dir="ltr"><span style="color:rgb(85,85,85);font-family:sans-serif;line-height:20px;background-color:rgb(255,255,255);border-width:2px 0px 0px;border-style:solid;border-color:rgb(213,15,37);padding-top:2px;margin-top:2px">Oleksiy Vyalov |</span><span style="color:rgb(85,85,85);font-family:sans-serif;line-height:20px;background-color:rgb(255,255,255);border-width:2px 0px 0px;border-style:solid;border-color:rgb(51,105,232);padding-top:2px;margin-top:2px"> Software Engineer |</span><span style="color:rgb(85,85,85);font-family:sans-serif;line-height:20px;background-color:rgb(255,255,255);border-width:2px 0px 0px;border-style:solid;border-color:rgb(0,153,57);padding-top:2px;margin-top:2px"> <a href="mailto:ovyalov@google.com" target="_blank">ovyalov<font color="#1155cc">@google.com</font></a></span></div></div>
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