Fix TransactionManager DefaultTimeout/MaximumTimeout setter race condition

[Copilot]

TransactionManager.DefaultTimeout has a race condition where a concurrent read can overwrite a value set by another thread. The getter uses LazyInitializer.EnsureInitialized (which acquires s_classSyncObject lock) while the setter used Interlocked.Exchange + a plain write to the s_defaultTimeoutValidated flag — outside any lock. A concurrent getter thread could see the flag as false, enter EnsureInitialized, acquire the lock, and overwrite the setter's new value with the config default.

Changes

• Perform all work in the DefaultTimeout and MaximumTimeout under a lock to ensure coherent state and avoid race conditions
• Delete unnecessary ceremony for default values that was left-over from .NET Framework configuration system

Fixes #105124

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[jkotas]

@copilot

• Delete MachineSettingsSection, ConfigurationStrings, DefaultSettingsSection. Inline the default values in the few places that they are used instead.
• Delete s_defaultTimeoutValidated and s_cachedMaxTimeout.
• Initialize s_defaultTimeoutTicks with default value: static long s_defaultTimeoutTicks = TimeSpan.FromMinutes(1).Ticks;
• Rename s_maximumTimeout to s_maximumTimeoutTicks and initialize it with default value: static long s_maximumTimeoutTicks = TimeSpan.FromMinutes(10).Ticks;
• Change DefaultTimeout getter to just return the static value:

TransactionsEtwProvider etwLog = TransactionsEtwProvider.Log;
if (etwLog.IsEnabled())
{
     etwLog.MethodEnter(TraceSourceType.TraceSourceBase, "TransactionManager.get_DefaultTimeout");
     etwLog.MethodExit(TraceSourceType.TraceSourceBase, "TransactionManager.get_DefaultTimeout");
}
return new TimeSpan(Interlocked.Read(ref s_defaultTimeoutTicks));

• Dtto for MaximumTimeout setter
• Change DefaultTimeout setter to take a lock around the validation and updates to ensure coherent state:

lock (ClassSyncObject)
{
    TimeSpan validatedTimeout = ValidateTimeout(value);
    Interlocked.Exchange(ref s_defaultTimeoutTicks, validatedTimeout.Ticks);
    timeoutAdjusted = validatedTimeout != value;
}
if (timeoutAdjusted)
{
    if (etwLog.IsEnabled())
    {
        etwLog.ConfiguredDefaultTimeoutAdjusted();
    }
}

• Change MaximumTimeout setter to take a lock around the validation and updates to ensure coherent state:

lock (ClassSyncObject)
{
    Interlocked.Exchange(ref s_maximumTimeoutTicks, value.Ticks);

    TimeSpan timeout = new TimeSpan(s_defaultTimeoutTicks);
    TimeSpan validatedTimeout = ValidateTimeout(value);
    Interlocked.Exchange(ref s_defaultTimeoutTicks, validatedTimeout.Ticks);
    timeoutAdjusted = validatedTimeout != timeout;
}
if (timeoutAdjusted)
{
    if (etwLog.IsEnabled())
    {
        etwLog.ConfiguredDefaultTimeoutAdjusted();
    }
}

• Update PR description to reflect the changes

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[Copilot]

@copilot

• Delete MachineSettingsSection, ConfigurationStrings, DefaultSettingsSection. Inline the default values in the few places that they are used instead.
  ...

Done in the latest commit. Here's a summary of all changes made:

• Deleted MachineSettingsSection.cs, ConfigurationStrings.cs, and DefaultSettingsSection.cs; removed them from the .csproj
• s_defaultTimeoutTicks initialized to TimeSpan.FromMinutes(1).Ticks
• s_maximumTimeout renamed to s_maximumTimeoutTicks (long) and initialized to TimeSpan.FromMinutes(10).Ticks
• s_defaultTimeoutValidated and s_cachedMaxTimeout deleted
• DefaultTimeout getter simplified to just ETW + Interlocked.Read
• MaximumTimeout getter simplified to just ETW + Interlocked.Read
• DefaultTimeout setter: ValidateTimeout and Interlocked.Exchange inside the lock, event fired outside
• MaximumTimeout setter: Interlocked.Exchange for the new max, then revalidate the current default timeout inside the lock, event fired outside
• DistributedTransactionManager inlined with ""

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[jkotas]

@steveisok Could you please approve this? The approval from @AndriySvyryd is not good enough for some reason.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

Suppressed comments (1)

src/libraries/System.Transactions.Local/src/System/Transactions/TransactionManager.cs:353

• Inside MaximumTimeout setter, s_defaultTimeoutTicks is read directly (new TimeSpan(s_defaultTimeoutTicks)) even though the field is otherwise accessed via Interlocked. While this is currently under the same lock as all writers, using Interlocked.Read here keeps the access pattern consistent and avoids relying on that invariant for correctness on 32-bit / future refactors.

                    TimeSpan timeout = new TimeSpan(s_defaultTimeoutTicks);