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Distributed Programming in Argus Barbara Liskov Papers We Love SF - January 2017

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Caitie McCaffrey @caitie Distributed Systems Engineer CaitieM.com

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1988

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“Technological advances have made it cost effective to construct large systems from collections of computer connected via networks. To support such systems, there is a growing need for effective way to organize and maintain distributed programs” Guardians and Actions: Linguistic Support for Robust, Distributed Programs

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Atomicity RPC &

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Guardians and Actions: Linguistic Support for Robust, Distributed Programs “We believe that the most desirable form of communication is the paired send and reply” Remote Procedure Calls

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Guardians and Actions: Linguistic Support for Robust, Distributed Programs “We believe the form of communication that is needed is remote procedure call with at-most-once semantics” Remote Procedure Calls

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Argus RPC In

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“a special kind of abstract object whose purpose is to encapsulate a resource” Guardians Distributed Programming in Argus

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“it permits its resource to be accessed by means of special procedures, called handlers” Handlers Distributed Programming in Argus

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Argus Banking with

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Branch Guardian Open (a: account_number) Close (a: account_number) Deposit (a: account_number, amt: int) Withdraw (a: account_number, amt: int) Total() Handlers

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Branch A Branch B Account 123 : $100 Account 456: $50 Account 789: $250 Open (123) Deposit(123, 100) Open (456) Deposit(456, 50) Open (789) Deposit(789, 250)

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Atomicity RPC &

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“An adequate language must provide a modular, reasonably automatic method for achieving consistency ” Atomicity Distributed Programming in Argus

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Guardians and Actions: Linguistic Support for Robust, Distributed Programs “Our solution to the problem of maintaining consistent distributed data in the face of concurrent, potentially interfering activities, and in the face of system failures such as node crashes and network disruptions while these activities are running is to make activities atomic” Atomicity

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Argus Atomicity In

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Serializable Actions Total (abort or commit)

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Atomic Abstract Data Type Atomic Objects Argus Provides: atomic arrays, records, variants, characters, and integers

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Read Write Lock Locking Rules Multiple Readers are Allowed Readers Exclude Writers Writer Exclude other Writers & Readers

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Distributed Programing in Argus “Computation in Argus starts as a top action at some guardian. The computation spreads to other guardians by means of handler calls. Execution of a handler call may cause some objects at the handler’s guardian to be modified, and may in turn lead to further calls”

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Argus Banking with

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Branch A Branch B Account 123 : $100 Account 456: $50 Account 789: $250 Transfer( amt: int, from: account_number, to: account_number)

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Branch B Account 789: $250 Branch A Account 123 : $100 Account 456: $50 SubAction: Deposit (123, 50) Transfer Action SubAction: Withdraw(789, 50) Transfer Deposit Withdraw

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Branch B Account 789: $250 Branch A Account 123 : $100 Account 456: $50 SubAction: Deposit (123, 50) Transfer Action SubAction: Withdraw(789, 50) Transfer Deposit Withdraw enter topaction coenter action branchA.Deposit(123, 50) action branchB.Withdraw(789, 50) end end

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Branch B Account 789: $250 Branch A Account 123 : $100 Account 456: $50 Deposit (123, 50) Transfer Action Withdraw(789, 50)

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Branch B Account 789: $250 Branch A Account 123 : $100 Account 456: $50 Deposit (123, 50) Transfer Action Withdraw(789, 50) Account 123 : $150 Account 789: $200 V1 V1

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Branch B Account 789: $250 Branch A Account 123 : $100 Account 456: $50 Deposit Success Transfer Action Withdraw Success Account 123 : $150 Account 789: $200 V1 V1

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Branch B Account 789: $250 Branch A Account 123 : $100 Account 456: $50 Transfer Action Account 123 : $150 Account 789: $200 V1 V1 Commit Top Level Action 2PC Transfer Deposit Withdraw

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Branch B Branch A Prepare Transfer Action Prepare Commit Top Level Action 2PC: Phase 1 V1 V1 Account 789: $250 Account 123 : $100 Account 456: $50 Account 123 : $150 Account 789: $200

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Branch B Branch A Prepare Success Transfer Action Prepare Success Commit Top Level Action 2PC: Phase 1 V1 V1 Account 789: $250 Account 123 : $100 Account 456: $50 Account 123 : $150 Account 789: $200

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Branch B Branch A Account 456: $50 Commit Transfer Action Commit Account 123 : $150 Account 789: $200 Commit Top Level Action 2PC : Phase 2

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Branch B Branch A Account 456: $50 Commit Success Transfer Action Commit Success Account 123 : $150 Account 789: $200 Commit Top Level Action 2PC : Complete

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Argus Banking with

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Branch B Account 789: $200 Branch A Account 123 : $150 Account 456: $50 SubAction: Deposit (123, 100) Transfer Action SubAction: Withdraw(456, 100) Transfer Deposit Withdraw

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Branch B Account 789: $200 Branch A Account 123 : $150 Account 456: $50 Deposit (123, 100) Transfer Action Withdraw(456, 100)

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Branch B Account 789: $200 Branch A Account 123 : $150 Account 456: $50 Deposit Success Transfer Action Withdraw Abort V1 Account 123 : $250 Transfer Deposit Withdraw

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Branch B Account 789: $200 Branch A Account 123 : $150 Account 456: $50 Abort Deposit Transfer Action V1 Account 123 : $250 Abort Top Level Action 2PC : Abort

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Branch B Account 789: $200 Branch A Account 123 : $150 Account 456: $50 Deposit Aborted Transfer Action Abort Top Level Action 2PC : Abort

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Branch B Account 789: $200 Branch A Account 123 : $150 Account 456: $50 Transfer Action

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Sub-Actions “Argus allows actions to be nested; thus an action can have one or more sub-actions“ Distributed Programming in Argus Transfer Deposit Withdraw

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Sub-Actions Replicate Action Replica A Replica B

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Sub-Actions Replicate Deposit Replica A Replica B Transfer Deposit Withdraw Replicate Withdraw Replica A Replica B

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Sub-Actions Replicate Deposit Replica A Replica B Transfer Deposit Withdraw Replicate Withdraw Replica A Replica B

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Sub-Actions Replicate Deposit Replica A Replica B Transfer Deposit Withdraw Replicate Withdraw Replica A Replica B

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Sub-Actions Replicate Deposit Replica A Replica B Transfer Deposit Withdraw Replicate Withdraw Replica A Replica B Abort

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Sub-Actions Replicate Deposit Replica A Replica B Transfer Deposit Withdraw Replicate Withdraw Replica A Replica B

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Sub-Actions Replicate Deposit Replica A Replica B Transfer Deposit Withdraw Replicate Withdraw Replica A Replica B

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Sub-Actions Replicate Deposit Replica A Replica B Transfer Deposit Withdraw Replicate Withdraw Replica A Replica B 2PC: Abort

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Sub-Actions “Argus runs every handler call as a sub-action…this extra action ensures that calls have a zero or one semantics.“ Distributed Programming in Argus

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What if Sub-Actions try to access the same atomic object?

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What if Sub-Actions try to access the same atomic object?

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Read Lock: All holders of write locks on x must be ancestors of S Write Lock: All holders of write locks on x must be ancestors of S. Locking Rules for Sub-Actions Distributed Programming in Argus

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Commit: S’s parent acquires S’s lock on x. If S holds a write lock on x, then S’s version becomes S’s parent version Abort: S’s lock and version (if any) are discarded Version Management Rules for Sub Actions Distributed Programming in Argus

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Sub Action Locking Account Balance Object $200 Value X Y Z 1.5% Interest 2% Interest Read Balance

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Account Balance Object $200 V1 $203 Value X Y Z 1.5% Interest 2% Interest Read Balance X: Write Lock (V1) Sub Action Locking

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Account Balance Object $200 V1 $203 V2 $207.06 Value X Y Z 1.5% Interest 2% Interest Read Balance X: Write Lock (V1) Y: Write Lock (V2) Sub Action Locking

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Account Balance Object $200 V1 $203 V2 $207.06 Value X Y Z W 1.5% Interest 2% Interest Read Balance .5% Interest X: Write Lock (V1) Y: Write Lock (V2) Z: Read Lock (V2) Sub Action Locking

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Account Balance Object $200 V1 $203 V2 V3 $207.06 $208.10 Value X Y Z W 1.5% Interest 2% Interest Read Balance .5% Interest X: Write Lock (V1) Y: Write Lock (V2) Z: Read Lock (V2) W: Write Lock (V3) Sub Action Locking

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Account Balance Object $200 V1 $203 X: Write Lock (V1) V2 V3 $207.06 $208.10 Value Y: Write Lock (V2) Z: Write Lock (V3) X Y Z W 1.5% Interest 2% Interest Read Balance .5% Interest Sub Action Locking

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Account Balance Object $200 V1 $203 X: Write Lock (V1) V2 V3 $207.06 $208.10 Value Y: Write Lock (V3) X Y Z W 1.5% Interest 2% Interest Read Balance .5% Interest Sub Action Locking

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Account Balance Object $200 V1 $203 X: Write Lock (V3) V2 V3 $207.06 $208.10 Value X Y Z W 1.5% Interest 2% Interest Read Balance .5% Interest Sub Action Locking

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Account Balance Object $200 V1 $203 X: Write Lock (V3) V2 V3 $207.06 $208.10 Value Y: Write Lock (V3) Z: Write Lock (V3) X Y Z W 1.5% Interest 2% Interest Read Balance .5% Interest Sub Action Locking Two Phase Commit

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Account Balance Object $208.10 Value X Y Z W 1.5% Interest 2% Interest Read Balance .5% Interest Sub Action Locking

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Problems with Argus

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“The concurrency that is built in to the mail system can lead to a number of deadlock situations” Guardians and Actions: Linguistic Support for Robust, Distributed Programs “As implemented most of the handlers can deadlock with other concurrent operations” Distributed Programming in Argus Deadlocks

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Deadlocks “The programmer must think about deadlocks and starvation and implement the code to avoid them when possible" Distributed Programming in Argus

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Blocking Calls “A new process is created to perform an incoming handler call …[so guardians can] have the ability to execute many request concurrently … if the guardian is running on a single-processor node, then only one process will be running at a time” Guardians and Actions: Linguistic Support for Robust, Distributed Programs

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Blocking Calls “A new process is created to perform an incoming handler call …[so guardians can] have the ability to execute many request concurrently … if the guardian is running on a single-processor node, then only one process will be running at a time” Guardians and Actions: Linguistic Support for Robust, Distributed Programs Promises: linguistic support for efficient asynchronous procedure calls in distributed systems B. Liskov, L.Shrira 1988

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So where do we go from here?

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“Guardians allow programs to be decomposed into units of tightly coupled data and processing” Distributed Programming in Argus Guardians

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Microservices

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“Atomic actions are an important tool both for understanding what a system should do and for implementing it correctly” Distributed Programming in Argus

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2014

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Halo 4: Statistics Service

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2015

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2015 “We focus our study on the common use of feral or a pplication-level, mechanisms for maintaining database integrity”

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2015

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CRDT * Stolen from Chris Meiklejohn in practice

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2012

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2012 “ Spanner is the first system to distribute data at global scale and support externally-consistent distributed transaction”

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2016

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Conclusion

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Thank You! @caitie