- •Contents
- •List of Figures
- •List of Tables
- •Acknowledgments
- •Introduction to MPI
- •Overview and Goals
- •Background of MPI-1.0
- •Background of MPI-1.1, MPI-1.2, and MPI-2.0
- •Background of MPI-1.3 and MPI-2.1
- •Background of MPI-2.2
- •Who Should Use This Standard?
- •What Platforms Are Targets For Implementation?
- •What Is Included In The Standard?
- •What Is Not Included In The Standard?
- •Organization of this Document
- •MPI Terms and Conventions
- •Document Notation
- •Naming Conventions
- •Semantic Terms
- •Data Types
- •Opaque Objects
- •Array Arguments
- •State
- •Named Constants
- •Choice
- •Addresses
- •Language Binding
- •Deprecated Names and Functions
- •Fortran Binding Issues
- •C Binding Issues
- •C++ Binding Issues
- •Functions and Macros
- •Processes
- •Error Handling
- •Implementation Issues
- •Independence of Basic Runtime Routines
- •Interaction with Signals
- •Examples
- •Point-to-Point Communication
- •Introduction
- •Blocking Send and Receive Operations
- •Blocking Send
- •Message Data
- •Message Envelope
- •Blocking Receive
- •Return Status
- •Passing MPI_STATUS_IGNORE for Status
- •Data Type Matching and Data Conversion
- •Type Matching Rules
- •Type MPI_CHARACTER
- •Data Conversion
- •Communication Modes
- •Semantics of Point-to-Point Communication
- •Buffer Allocation and Usage
- •Nonblocking Communication
- •Communication Request Objects
- •Communication Initiation
- •Communication Completion
- •Semantics of Nonblocking Communications
- •Multiple Completions
- •Non-destructive Test of status
- •Probe and Cancel
- •Persistent Communication Requests
- •Send-Receive
- •Null Processes
- •Datatypes
- •Derived Datatypes
- •Type Constructors with Explicit Addresses
- •Datatype Constructors
- •Subarray Datatype Constructor
- •Distributed Array Datatype Constructor
- •Address and Size Functions
- •Lower-Bound and Upper-Bound Markers
- •Extent and Bounds of Datatypes
- •True Extent of Datatypes
- •Commit and Free
- •Duplicating a Datatype
- •Use of General Datatypes in Communication
- •Correct Use of Addresses
- •Decoding a Datatype
- •Examples
- •Pack and Unpack
- •Canonical MPI_PACK and MPI_UNPACK
- •Collective Communication
- •Introduction and Overview
- •Communicator Argument
- •Applying Collective Operations to Intercommunicators
- •Barrier Synchronization
- •Broadcast
- •Example using MPI_BCAST
- •Gather
- •Examples using MPI_GATHER, MPI_GATHERV
- •Scatter
- •Examples using MPI_SCATTER, MPI_SCATTERV
- •Example using MPI_ALLGATHER
- •All-to-All Scatter/Gather
- •Global Reduction Operations
- •Reduce
- •Signed Characters and Reductions
- •MINLOC and MAXLOC
- •All-Reduce
- •Process-local reduction
- •Reduce-Scatter
- •MPI_REDUCE_SCATTER_BLOCK
- •MPI_REDUCE_SCATTER
- •Scan
- •Inclusive Scan
- •Exclusive Scan
- •Example using MPI_SCAN
- •Correctness
- •Introduction
- •Features Needed to Support Libraries
- •MPI's Support for Libraries
- •Basic Concepts
- •Groups
- •Contexts
- •Intra-Communicators
- •Group Management
- •Group Accessors
- •Group Constructors
- •Group Destructors
- •Communicator Management
- •Communicator Accessors
- •Communicator Constructors
- •Communicator Destructors
- •Motivating Examples
- •Current Practice #1
- •Current Practice #2
- •(Approximate) Current Practice #3
- •Example #4
- •Library Example #1
- •Library Example #2
- •Inter-Communication
- •Inter-communicator Accessors
- •Inter-communicator Operations
- •Inter-Communication Examples
- •Caching
- •Functionality
- •Communicators
- •Windows
- •Datatypes
- •Error Class for Invalid Keyval
- •Attributes Example
- •Naming Objects
- •Formalizing the Loosely Synchronous Model
- •Basic Statements
- •Models of Execution
- •Static communicator allocation
- •Dynamic communicator allocation
- •The General case
- •Process Topologies
- •Introduction
- •Virtual Topologies
- •Embedding in MPI
- •Overview of the Functions
- •Topology Constructors
- •Cartesian Constructor
- •Cartesian Convenience Function: MPI_DIMS_CREATE
- •General (Graph) Constructor
- •Distributed (Graph) Constructor
- •Topology Inquiry Functions
- •Cartesian Shift Coordinates
- •Partitioning of Cartesian structures
- •Low-Level Topology Functions
- •An Application Example
- •MPI Environmental Management
- •Implementation Information
- •Version Inquiries
- •Environmental Inquiries
- •Tag Values
- •Host Rank
- •IO Rank
- •Clock Synchronization
- •Memory Allocation
- •Error Handling
- •Error Handlers for Communicators
- •Error Handlers for Windows
- •Error Handlers for Files
- •Freeing Errorhandlers and Retrieving Error Strings
- •Error Codes and Classes
- •Error Classes, Error Codes, and Error Handlers
- •Timers and Synchronization
- •Startup
- •Allowing User Functions at Process Termination
- •Determining Whether MPI Has Finished
- •Portable MPI Process Startup
- •The Info Object
- •Process Creation and Management
- •Introduction
- •The Dynamic Process Model
- •Starting Processes
- •The Runtime Environment
- •Process Manager Interface
- •Processes in MPI
- •Starting Processes and Establishing Communication
- •Reserved Keys
- •Spawn Example
- •Manager-worker Example, Using MPI_COMM_SPAWN.
- •Establishing Communication
- •Names, Addresses, Ports, and All That
- •Server Routines
- •Client Routines
- •Name Publishing
- •Reserved Key Values
- •Client/Server Examples
- •Ocean/Atmosphere - Relies on Name Publishing
- •Simple Client-Server Example.
- •Other Functionality
- •Universe Size
- •Singleton MPI_INIT
- •MPI_APPNUM
- •Releasing Connections
- •Another Way to Establish MPI Communication
- •One-Sided Communications
- •Introduction
- •Initialization
- •Window Creation
- •Window Attributes
- •Communication Calls
- •Examples
- •Accumulate Functions
- •Synchronization Calls
- •Fence
- •General Active Target Synchronization
- •Lock
- •Assertions
- •Examples
- •Error Handling
- •Error Handlers
- •Error Classes
- •Semantics and Correctness
- •Atomicity
- •Progress
- •Registers and Compiler Optimizations
- •External Interfaces
- •Introduction
- •Generalized Requests
- •Examples
- •Associating Information with Status
- •MPI and Threads
- •General
- •Initialization
- •Introduction
- •File Manipulation
- •Opening a File
- •Closing a File
- •Deleting a File
- •Resizing a File
- •Preallocating Space for a File
- •Querying the Size of a File
- •Querying File Parameters
- •File Info
- •Reserved File Hints
- •File Views
- •Data Access
- •Data Access Routines
- •Positioning
- •Synchronism
- •Coordination
- •Data Access Conventions
- •Data Access with Individual File Pointers
- •Data Access with Shared File Pointers
- •Noncollective Operations
- •Collective Operations
- •Seek
- •Split Collective Data Access Routines
- •File Interoperability
- •Datatypes for File Interoperability
- •Extent Callback
- •Datarep Conversion Functions
- •Matching Data Representations
- •Consistency and Semantics
- •File Consistency
- •Random Access vs. Sequential Files
- •Progress
- •Collective File Operations
- •Type Matching
- •Logical vs. Physical File Layout
- •File Size
- •Examples
- •Asynchronous I/O
- •I/O Error Handling
- •I/O Error Classes
- •Examples
- •Subarray Filetype Constructor
- •Requirements
- •Discussion
- •Logic of the Design
- •Examples
- •MPI Library Implementation
- •Systems with Weak Symbols
- •Systems Without Weak Symbols
- •Complications
- •Multiple Counting
- •Linker Oddities
- •Multiple Levels of Interception
- •Deprecated Functions
- •Deprecated since MPI-2.0
- •Deprecated since MPI-2.2
- •Language Bindings
- •Overview
- •Design
- •C++ Classes for MPI
- •Class Member Functions for MPI
- •Semantics
- •C++ Datatypes
- •Communicators
- •Exceptions
- •Mixed-Language Operability
- •Problems With Fortran Bindings for MPI
- •Problems Due to Strong Typing
- •Problems Due to Data Copying and Sequence Association
- •Special Constants
- •Fortran 90 Derived Types
- •A Problem with Register Optimization
- •Basic Fortran Support
- •Extended Fortran Support
- •The mpi Module
- •No Type Mismatch Problems for Subroutines with Choice Arguments
- •Additional Support for Fortran Numeric Intrinsic Types
- •Language Interoperability
- •Introduction
- •Assumptions
- •Initialization
- •Transfer of Handles
- •Status
- •MPI Opaque Objects
- •Datatypes
- •Callback Functions
- •Error Handlers
- •Reduce Operations
- •Addresses
- •Attributes
- •Extra State
- •Constants
- •Interlanguage Communication
- •Language Bindings Summary
- •Groups, Contexts, Communicators, and Caching Fortran Bindings
- •External Interfaces C++ Bindings
- •Change-Log
- •Bibliography
- •Examples Index
- •MPI Declarations Index
- •MPI Function Index
6.6. INTER-COMMUNICATION |
221 |
Group 0 |
Group 1 |
Group 2 |
Figure 6.3: Three-group pipeline.
LOGICAL HIGH
fMPI::Intracomm MPI::Intercomm::Merge(bool high) const (binding deprecated, see Section 15.2) g
This function creates an intra-communicator from the union of the two groups that are associated with intercomm. All processes should provide the same high value within each of the two groups. If processes in one group provided the value high = false and processes in the other group provided the value high = true then the union orders the \low" group before the \high" group. If all processes provided the same high argument then the order of the union is arbitrary. This call is blocking and collective within the union of the two groups.
The error handler on the new intercommunicator in each process is inherited from the communicator that contributes the local group. Note that this can result in di erent processes in the same communicator having di erent error handlers.
Advice to implementors. The implementation of MPI_INTERCOMM_MERGE,
MPI_COMM_FREE and MPI_COMM_DUP are similar to the implementation of MPI_INTERCOMM_CREATE, except that contexts private to the input inter-com- municator are used for communication between group leaders rather than contexts inside a bridge communicator. (End of advice to implementors.)
6.6.3 Inter-Communication Examples
Example 1: Three-Group \Pipeline"
Groups 0 and 1 communicate. Groups 1 and 2 communicate. Therefore, group 0 requires one inter-communicator, group 1 requires two inter-communicators, and group 2 requires 1 inter-communicator.
int main(int |
argc, char **argv) |
||
{ |
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MPI_Comm |
myComm; |
/* intra-communicator of local sub-group */ |
|
MPI_Comm |
myFirstComm; |
/* |
inter-communicator */ |
MPI_Comm |
mySecondComm; /* |
second inter-communicator (group 1 only) */ |
|
int membershipKey; int rank;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
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222 CHAPTER 6. GROUPS, CONTEXTS, COMMUNICATORS, AND CACHING
1/* User code must generate membershipKey in the range [0, 1, 2] */
2
3
membershipKey = rank % 3;
4/* Build intra-communicator for local sub-group */
5MPI_Comm_split(MPI_COMM_WORLD, membershipKey, rank, &myComm);
6
7/* Build inter-communicators. Tags are hard-coded. */
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if (membershipKey == 0) |
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{ |
/* Group 0 communicates with |
group 1. */ |
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MPI_Intercomm_create( |
myComm, 0, MPI_COMM_WORLD, |
1, |
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1, &myFirstComm); |
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} |
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else if (membershipKey == 1) |
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{ |
/* Group |
1 communicates with groups |
0 and 2. */ |
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MPI_Intercomm_create( |
myComm, 0, MPI_COMM_WORLD, |
0, |
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1, &myFirstComm); |
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MPI_Intercomm_create( |
myComm, 0, MPI_COMM_WORLD, |
2, |
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12, &mySecondComm); |
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} |
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else if (membershipKey == 2) |
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{ |
/* Group 2 communicates with |
group 1. */ |
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MPI_Intercomm_create( |
myComm, 0, MPI_COMM_WORLD, |
1, |
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12, &myFirstComm); |
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} |
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/* Do work ... */
28switch(membershipKey) /* free communicators appropriately */
29{
30case 1:
31MPI_Comm_free(&mySecondComm);
32case 0:
33case 2:
34MPI_Comm_free(&myFirstComm);
35break;
36}
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41
MPI_Finalize();
}
42 Example 2: Three-Group \Ring"
43
Groups 0 and 1 communicate. Groups 1 and 2 communicate. Groups 0 and 2 communicate.
44
Therefore, each requires two inter-communicators.
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int main(int argc, char **argv)
{
MPI_Comm |
myComm; |
/* intra-communicator of local sub-group */ |
6.6. INTER-COMMUNICATION |
223 |
Group 0 |
Group 1 |
Group 2 |
|
Figure 6.4: Three-group ring. |
MPI_Comm |
myFirstComm; /* inter-communicators */ |
MPI_Comm |
mySecondComm; |
MPI_Status |
status; |
int membershipKey; int rank;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
...
/* User code must generate membershipKey in the range [0, 1, 2] */ membershipKey = rank % 3;
/* Build intra-communicator for local sub-group */ MPI_Comm_split(MPI_COMM_WORLD, membershipKey, rank, &myComm);
/* Build inter-communicators. Tags are hard-coded. */ if (membershipKey == 0)
{ |
/* Group 0 communicates with groups 1 and 2. */ |
|||
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MPI_Intercomm_create( |
myComm, |
0, |
MPI_COMM_WORLD, 1, |
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1, &myFirstComm); |
||
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MPI_Intercomm_create( |
myComm, |
0, |
MPI_COMM_WORLD, 2, |
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2, &mySecondComm); |
||
}
else if (membershipKey == 1)
{ /* Group 1 communicates with groups 0 and 2. */ MPI_Intercomm_create( myComm, 0, MPI_COMM_WORLD, 0,
1, &myFirstComm); MPI_Intercomm_create( myComm, 0, MPI_COMM_WORLD, 2,
12, &mySecondComm);
}
else if (membershipKey == 2)
{ /* Group 2 communicates with groups 0 and 1. */ MPI_Intercomm_create( myComm, 0, MPI_COMM_WORLD, 0,
2, &myFirstComm); MPI_Intercomm_create( myComm, 0, MPI_COMM_WORLD, 1,
12, &mySecondComm);
}
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