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SYSLIB0004: The constrained execution region (CER) feature is not supported

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The Constrained execution regions (CER) feature is supported only in .NET Framework. As such, various CER-related APIs are marked obsolete, starting in .NET 5. Using these APIs generates warning SYSLIB0004 at compile time.

The following CER-related APIs are obsolete:

However, the following CER-related APIs are not obsolete:

Workarounds

  • If you've applied a CER attribute to a method, remove the attribute. These attributes have no effect in .NET 5 and later versions.

    // REMOVE the attribute below.
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
public void DoSomething()
{
}

// REMOVE the attribute below.
[PrePrepareMethod]
public void DoSomething()
{
}

  • If you are calling RuntimeHelpers.ProbeForSufficientStack or RuntimeHelpers.PrepareContractedDelegate, remove the call. These calls have no effect in .NET 5 and later versions.

    public void DoSomething()
{
    // REMOVE the call below.
    RuntimeHelpers.ProbeForSufficientStack();

    // (Remainder of your method logic here.)
}

  • If you are calling RuntimeHelpers.PrepareConstrainedRegions, remove the call. This call has no effect in .NET 5 and later versions.

    public void DoSomething_Old()
{
    // REMOVE the call below.
    RuntimeHelpers.PrepareConstrainedRegions();
    try
    {
        // try code
    }
    finally
    {
        // cleanup code
    }
}

public void DoSomething_Corrected()
{
    // There is no call to PrepareConstrainedRegions. It's a normal try / finally block.

    try
    {
        // try code
    }
    finally
    {
        // cleanup code
    }
}

  • If you are calling RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup, replace the call with a standard try/catch/finally block.

    // The sample below produces warning SYSLIB0004.
public void DoSomething_Old()
{
    RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(MyTryCode, MyCleanupCode, null);
}
public void MyTryCode(object state) { /* try code */ }
public void MyCleanupCode(object state, bool exceptionThrown) { /* cleanup code */ }

// The corrected sample below does not produce warning SYSLIB0004.
public void DoSomething_Corrected()
{
    try
    {
        // try code
    }
    catch (Exception ex)
    {
        // exception handling code
    }
    finally
    {
        // cleanup code
    }
}

Suppress a warning

If you must use the obsolete APIs, you can suppress the warning in code or in your project file.

To suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the warning.

// Disable the warning.
#pragma warning disable SYSLIB0004

// Code that uses obsolete API.
// ...

// Re-enable the warning.
#pragma warning restore SYSLIB0004

To suppress all the SYSLIB0004 warnings in your project, add a <NoWarn> property to your project file.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
   ...
   <NoWarn>$(NoWarn);SYSLIB0004</NoWarn>
  </PropertyGroup>
</Project>

For more information, see Suppress warnings.

See also