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Safer safehandle #32

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garuma wants to merge 3 commits into from
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Safer safehandle #32

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cb100fb
[SafeHandle] Protect Close against asynchronous exceptions
garuma Dec 1, 2010
b07b00e
[SafeHandle] Make success parameter setting atomic wrt async exceptio…
garuma Dec 1, 2010
72d878c
[SafeHandle] Add bits of documentation
garuma Dec 1, 2010
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50 changes: 36 additions & 14 deletions mcs/class/corlib/System.Runtime.InteropServices/SafeHandle.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -30,12 +30,14 @@
// For details, see:
// http://blogs.msdn.com/cbrumme/archive/2004/02/20/77460.aspx
//
// CER-like behavior is implemented for Close and DangerousAddRef
// via the try/finally uninterruptible pattern in case of async
// exceptions like ThreadAbortException.
//
// On implementing SafeHandles:
// http://blogs.msdn.com/bclteam/archive/2005/03/15/396335.aspx
//
// Issues:
// The System.Runtime.ConstrainedExecution.ReliabilityContractAttribute has
// not been applied to any APIs here yet.
//
// TODO: Although DangerousAddRef has been implemented, I need to
// find out whether the runtime performs the P/Invoke if the
Expand All @@ -46,6 +48,7 @@
using System;
using System.Runtime.InteropServices;
using System.Runtime.ConstrainedExecution;
using System.Runtime.CompilerServices;
using System.Threading;

namespace System.Runtime.InteropServices
Expand Down Expand Up @@ -81,16 +84,27 @@ public void Close ()
if (refcount == 0)
throw new ObjectDisposedException (GetType ().FullName);

int newcount, current;
do {
current = refcount;
newcount = current-1;
} while (Interlocked.CompareExchange (ref refcount, newcount, current) != current);

if (newcount == 0 && owns_handle && !IsInvalid){
ReleaseHandle ();
handle = invalid_handle_value;
refcount = -1;
int newcount = 0, current = 0;
bool registered = false;
RuntimeHelpers.PrepareConstrainedRegions ();
try {
do {
current = refcount;
newcount = current-1;

// See notes for explanation
try {}
finally {
if (Interlocked.CompareExchange (ref refcount, newcount, current) == current)
registered = true;
}
} while (!registered);
} finally {
if (registered && newcount == 0 && owns_handle && !IsInvalid){
ReleaseHandle ();
handle = invalid_handle_value;
refcount = -1;
}
}
}

Expand All @@ -109,6 +123,7 @@ public void DangerousAddRef (ref bool success)
if (refcount <= 0)
throw new ObjectDisposedException (GetType ().FullName);

bool registered = false;
int newcount, current;
do {
current = refcount;
Expand All @@ -123,8 +138,15 @@ public void DangerousAddRef (ref bool success)
//
throw new ObjectDisposedException (GetType ().FullName);
}
} while (Interlocked.CompareExchange (ref refcount, newcount, current) != current);
success = true;

// See notes for explanations
RuntimeHelpers.PrepareConstrainedRegions ();
try {}
finally {
if (Interlocked.CompareExchange (ref refcount, newcount, current) == current)
registered = success = true;
}
} while (!registered);
}

[ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
Expand Down