Initial commit of Swage libraries to public repo.

.gitignore

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+.idea
+*.iml
+/out
+target/

LICENSE

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NOTICE

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+Swage
+Copyright 2017 Amazon.com, Inc. or its affiliates. All Rights Reserved. 

README.md

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+# Swage
+
+Swage is a collection of libraries useful for developing and running services.
+
+Currently it consists of the following Java libraries:
+* Metrics
+* Type Safe
+* Thread Context
+* Disseminating Executors
+
+
+## Metrics
+
+The Swage Metrics library provides a clean, robust API for recording metric
+events in a Java application, as well as a core implementation for sending the
+instrumented metric data to AWS CloudWatch.
+
+It consists of the following modules:
+* metrics-core
+* metrics-api
+
+## Type Safe
+
+Swage Type Safe is a small library that provides type-safe solutions that are
+not part of the Java standard libraries.  At the moment it consists soley of
+the TypedMap, a class for storing heterogenous key/value pairs in a a type safe
+way.
+
+It lives in the type-safe module.
+
+
+## Thread Context
+
+Swage Thread Context is a library to help manage and propagate task context in
+an application across threads.  Where a ThreadLocal can help manage context
+within one thread, this library provides a way to manage context where a task
+may span many threads.
+
+It lives in the thread-context module.
+
+
+## Disseminating Executors
+
+The Disseminating Executors library solves the same basic problem as the Thread
+Context library, but with a different approach.  Ths library is intended to
+allow targetd state to cross thread boundaries without invasive changes at
+every execution point.  It uses custom task executors to capture and propagate
+state.
+
+It lives in the disseminating-executors module.

disseminating-executors/README.md

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+# State Captures
+
+This library is intended to allow targeted state to cross thread
+boundaries without invasive changes at every execution point. In
+particular, this enables the developers of framework components the
+ability to, with higher confidence than before, transition their
+thread-local state through multiple thread pools to some relevant exit
+point.
+
+# Example usage
+
+```java
+ExecutorService e = Executors.newCachedThreadPool();
+e = StateCapture.capturingDecorator(e);
+```
+
+# Getting started
+
+For application owners, wrap your `Executors`, `ExecutorService`s
+and `CompletionService`s with `StateCapture.capturingDecorator()`.
+If passing a lambda to a library that controls its own thread pool,
+an application can call `StateCapture.capturingDecorator()` on
+the runnable or callable itself.
+
+# Design goals
+## Motivating example: tracing
+
+A tracing module to a framework could place the data
+they would like to transfer from the entry point to a service to
+the other web clients, so tracing identifiers can be propagated over
+the wire. Tracing is a system-wide cross-cutting concern, but making
+every simple application explicitly wire through all tracing state is
+tedious. For applications that are entirely single-threaded, this is
+simple: just use an ordinary thread local. Unfortunately, this breaks
+at the first use of any executors, commonly used for asynchronous IO.
+
+If the executors are aware of the data that needs to be moved, then
+there's no problem - the data can be copied from one thread to the next.
+However, modifying all points in execution to make this copying happen
+is often a prohibitive amount of work. Making it possible to implement
+applications and frameworks in a forward-compatible way for these
+scenarios should reduce maintenance costs and long-term burden.
+
+## Motivating example: Logging
+
+Logging setups frequently reference thread-local data to put
+information in logs. Log4j 2.x, for example, has both a
+"thread context stack" and a "thread context map". Log formats
+can refer to variables in these thread context variables.
+
+High quality logs have a huge impact on the operational ability
+of teams to identify and fix issues in production, and log metadata
+working as expected across thread boundaries helps reduce MTTR.
+
+Log4j 2.x doesn't provide a convenient mechanism to move data across
+threads and, even if it did, it would be logging-framework specific.
+There is no general solution that multiple logging frameworks have
+adopted. A good solution to this problem should be able to work with
+any logging framework, including ones not yet identified, or any
+other third-party framework with similar requirements. It should not
+require the third-party to make invasive changes to enable this;
+ideally it would require no changes at all.
+
+## Motivating example: non-thread-safe child objects
+
+Some libraries aren't thread safe, but also have some state that
+needs to move from thread to thread. In these cases, a child object
+can be created with the required metadata and passed into the next
+thread. These objects also sometimes require some kind of cleanup
+to occur; this should also be possible.
+
+# Functionality
+This library seeks to address all of the motivating scenarios by
+being unopinionated about the needs of different libraries and
+making it possible for them to implement however fits their world
+view. By providing hooks to provide data to pass across a thread
+boundary and to execute code before and after executing the real
+business task, libraries can do whatever they need to do.
+
+## High-level implementation
+
+At a high level, this library allows state to be captured or created
+by a calling thread in a plugin, moved to the scope of a calling thread,
+then the plugins are given execution control of the data from within
+the called thread.
+
+1. A method like `submit()` is called on a wrapped executor
+2. Every plugin is asked for an object representing captured state
+3. The callee thread begins execution
+4. A before method is called on the object containing the captured state
+5. The actual method is called
+6. An after method is called on the object containing the captured state
+
+## Limitations
+
+This library is not a silver bullet. For example, if data is
+transferred from one thread to another via a shared reference
+to a concurrent data structure, there is no opportunity for
+captured state to be created or processed. This also cannot transfer
+data across other boundaries that do not participate. For example,
+a library may have its own thread pool and create its own tasks. This
+library does not provide a mechanism to make all thread pools
+capture and move state.
+
+# Application integration
+## Single-threaded applications
+Applications that use a single thread don't need to do anything
+## Applications with thread pools
+Applications that use thread pools need to wrap all the thread pools
+they wish to capture state with a state capturing decorator.
+## Applications that use shared data structures to pass data between threads
+These applications will need to integrate with their various
+frameworks and tools through some manual manner since there
+is no automatable mechanism to transfer state between threads
+in this case.
+# Tool integration
+
+Tools that want to capture and move state with this mechanism must
+implement two interfaces: `CapturedState`
+and `StateCaptor`. Additionally,
+the implemented `StateCaptor` should include in the jar via
+the [`ServiceLoader`][1]. To use this, put a text file at
+`META-INF/services/StateCaptor`
+with each fully qualified implementation of `StateCaptor` on
+its own line. These will be picked up and used at runtime. This can also
+be achieved using [Google's AutoService][2].
+
+[1]: http://docs.oracle.com/javase/8/docs/api/java/util/ServiceLoader.html
+[2]: https://github.com/google/auto/tree/master/service