Polly 5.1.1-v5-x-cachealpha0001

v5.0 is a major release with significant new resilience policies: Timeout; Bulkhead Isolation; Fallback; and PolicyWrap. See release notes back to v5.0.0 for full details.

 5.x-cachealpha
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 - Exposes central infrastructure for forthcoming CachePolicy, so that implementations of ICacheProvider, ICacheKeyStrategy, ITtlStrategy and ICacheItemSerializer can be coded against it.  
 - ALPHA STATUS: refinement may occur.   

 5.1.0
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 - Allow different parts of a policy execution to exchange data via a mutable Context travelling with each execution.

 5.0.6
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 - Update NETStandard.Library dependency to latest 1.6.1 for .NetStandard1.0 target.  Resolves compatibility for some Xamarin targets.

 5.0.5
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 - Bug fix: Prevent request stampede during half-open state of CircuitBreaker and AdvancedCircuitBreaker.  Enforce only one new trial call per break duration, during half-open state.
 - Bug fix: Prevent duplicate raising of the onBreak delegate, if executions started when a circuit was closed, return faults when a circuit has already opened.
 - Optimisation: Optimise hotpaths for Circuit-Breaker, Retry and Fallback policies.
 - Add NoOpPolicy: NoOpPolicy executes delegates without intervention; for eg stubbing out Polly in unit testing.

 5.0.4 pre
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 - (.NET40Async package changes only)

 5.0.3 RTM
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 - Refine implementation of cancellable synchronous WaitAndRetry
 - Minor breaking change: Where a user delegate does not observe cancellation, Polly will now honour the delegate's outcome rather than throw for the unobserved cancellation (issue 188).

 5.0.2 alpha
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 - .NETStandard1.0 target: Correctly state dependencies. 
 - .NETStandard1.0 target: Fix SemVer stamping of Polly.dll.
 - PCL259 project and target: Remove, in favour of .NETStandard1.0 target.  PCL259 targets are still supported, via .NETStandard1.0 target.
 - Mark Polly.dll as CLSCompliant.
 
 5.0.1 alpha
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 - Add a .NETStandard1.0 target.

 5.0.0 alpha
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 A major release, adding significant new resilience policies:
 - Timeout policy: allows timing out any execution
 - Bulkhead isolation policy: limits the resources consumable by governed actions, such that a faulting channel cannot cause cascading failures.
 - Fallback policy: provides for a fallback execution or value, in case of overall failure
 - PolicyWrap: allows flexibly combining Policy instances of any type, to form an overall resilience strategy.

 Other changes include:
 - Add PolicyKeys and context to all policy executions, for logging and to support later introduction of policy events and metrics. 
 - Add CancellationToken support to synchronous executions.
 - Add some missing ExecuteAndCapture/Async overloads. 
 - Remove invalid ExecuteAsync overloads taking (but not making use of) a CancellationToken
 - Provide .NET4.0 support uniquely through Polly.NET40Async package
 - Retire ContextualPolicy (not part of documented API; support now in Policy base class)
 - Discontinue .NET3.5 support

 4.3.0
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 - Added ability for policies to handle return results.  Optimised circuit-breaker hot path.  Fixed circuit-breaker threshold bug.  
 
 4.2.4
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 - Added overloads to WaitAndRetry and WaitAndRetryAsync methods that accept an onRetry delegate which includes the attempt count.
 
 4.2.3
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 - Cleaned up new Polly.Net40Async NuGet package, removing Polly.dll and unused framework folders.
 
 4.2.2
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 - Add new Polly.Net40Async project supporting async for .NET40 via Microsoft.Bcl.Async.  This is available as separate Nuget packages Polly.Net40Async and Polly.Net40Async-signed.

 4.2.1
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 - Allowed async onRetry delegates to async retry policies.

 4.2.0
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 - Added AdvancedCircuitBreaker - Thanks to @reisenberger and @kristianhald
 
 4.1.2
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 - Fixed an issue with the onReset delegate of the CircuitBreaker.
 
 4.1.1
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 - Add ExecuteAndCapture support with arbitrary context data - Thanks to @reisenberger
 
 4.1.0 
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 - Add Wait and retry forever policy - Thanks to @nedstoyanov 
 - Remove time-limit on CircuitBreaker state-change delegates - Thanks to @reisenberger 
 
 4.0.0 
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 - Add async support and circuit-breaker support for ContextualPolicy 
 - Add manual control of circuit-breaker (reset and manual circuit isolation) 
 - Add public reporting of circuit-breaker state, for health/performance monitoring 
 - Add delegates on changes of circuit state - Thanks to @reisenberger 
 
 3.0.0 
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 - Add cancellation support for all async Policy execution - Thanks to @reisenberger 
 
 2.2.7 
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 - Fixes an issue where continueOnCapturedContext needed to be specified in two places (on action execution and Policy configuration), when wanting to flow async action execution on the captured context - Thanks to @reisenberger 
 - Fixes excess line ending issues 
 
 2.2.6 
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 - Async sleep fix, plus added continueOnCapturedContext parameter on async methods to control whether continuation and retry will run on captured synchronization context - Thanks to @yevhen 
 
 2.2.5
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 - Policies with a retry count of zero are now allowed
 
 2.2.4
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 - Add .NET Core support
 
 2.2.3
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 - Fix PCL implementation of `SystemClock.Reset`
 - Added ability to capture the results of executing a policy via `ExecuteAndCapture`
 
 2.2.2
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 - Added extra `NotOnCapturedContext` call to prevent potential deadlocks when blocking on asynchronous calls
 
 2.2.1
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 - Replaced non-blocking sleep implementation with a blocking one for PCL
 
 2.2.0
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 - Added Async Support (PCL)
 - PCL Profile updated from Profile78 ->  Profile 259
 - Added missing WaitAndRetryAsync overload
 
 2.1.0
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 - Added Async Support (.NET Framework 4.5 Only)
 
 2.0.0
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 - Added Portable Class Library
 - The "Polly" NuGet package is now no longer strongly named. The strongly named NuGet package is now "Polly-Signed"
 
 1.1.0
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 - Added additional overloads to Retry
 - Allow arbitrary data to be passed to policy execution