Title: COMP309/509 - Lecture 15
class: middle, center, inverse
COMP309/509 - Parallel and Distributed Computing
Lecture 15 - Programming with PVM
By Mitchell Welch
University of New England
Reading
Summary
- Communication and Synchronisation in PVM
- Single Program Multiple Data Paradigm
- PVM Synchronisation
man Page Items
Communication and Synchronisation in PVM
- Communication is asynchronous:
- A send returns immediately, the message is on its way.
- Some message ordering is guaranteed.
- To send you go through these steps:
- Initialise the buffer.
- Pack the buffer.
- Send the buffer.
- Receiving must be done explicitly.
- Unpacking must be done in the same order it was packed.
Communication and Synchronisation in PVM
- Synchronization in PVM is limited.
- There is no shared memory.
- One form of synchronzation is barriers
- We’ll discuss them in more detail after an example.
Single Program Multiple Data Paradigm
spmd2.c spawns itself so this is the SP paradigm.- In this example we use groups to
- synchronize with the rest of the group.
- find out our rank in the group.
- find out the tids of neighbours in a ring configuration.
- sychronization by token ring
- pass a token around a ring
- the node with the token has exclusive access to the critical section
- it executes the critical section of code,
- then passes the token to the next node in the ring.
Single Program Multiple Data Paradigm
- When using groups we need to link with gpvm3:
all: spmd2
spmd2: spmd2.c
gcc -Wall spmd.c -lpvm3 -lgpvm3 -o spmd2
host:
cp -f spmd ${HOME}/pvm3/bin/LINUXI386/
clean:
rm -f spmd2 *~
Single Program Multiple Data Paradigm
Single Program Multiple Data Paradigm
- pvm directs output from spawned tasks to a file.
- Not to the terminal.
- Since that, after all, may be on another machine.
- The file is called
pvml.<your uid> in the /tmp/ directory
- To find your user id, use id:
bourbaki.Examples> id
uid=3191(comp309) gid=6310(admin) groups=6310(admin)
bourbaki.Examples>
bourbaki.une.edu.au.Examples> ./spmd2
me = 0 mytid = 262155
token ring done
bourbaki.une.edu.au.Examples>
bourbaki.une.edu.au.Examples> id
uid=794(comp381) gid=6310(admin) groups=6310(admin)
bourbaki.une.edu.au.Examples> more /tmp/pvml.794
...
[t80040000] 09/30 12:44:27 [t40072] me = 13 mytid = 262258
[t80040000] 09/30 12:44:27 [t40073] me = 14 mytid = 262259
[t80040000] 09/30 12:44:27 [t40074] me = 15 mytid = 262260
[t80040000] 09/30 12:44:27 [t40066] I'm ring node 1
[t80040000] 09/30 12:44:27 [t40066] I'm ring node 1 with token -9
[t80040000] 09/30 12:44:27 [t40067] I'm ring node 2
[t80040000] 09/30 12:44:27 [t40067] I'm ring node 2 with token -9
[t80040000] 09/30 12:44:27 [t40068] I'm ring node 3
[t80040000] 09/30 12:44:27 [t40068] I'm ring node 3 with token -9
[t80040000] 09/30 12:44:27 [t40069] I'm ring node 4
[t80040000] 09/30 12:44:27 [t40069] I'm ring node 4 with token -9
...
bourbaki.une.edu.au.Examples>
PVM Synchronisation man Page Items
- The
pvm_joingroup enrolls the calling process in a named group.
- A typical call:
int inum = pvm_joingroup(char *group);
group is the name of the group, a C string, i.e. a NULL terminated array of char.inum is the membership number.inum starts at 0 and increases.- If
inum is negative an error occurred.
PVM Synchronisation man Page Items
- When using groups a (
group, inum) pair uniquely identifies a PVM process.
- If a task leaves a group by calling
pvm_lvgroup and later rejoins the same group, the task is not guaranteed to get the same instance number.
- PVM attempts to reuse old instance numbers, so when a task joins a group it will get the lowest available instance number.
- A task can be a member of multiple groups simultaneously.
Example use:
inum = pvm_joingroup("Brett's Big BAD Group");
PVM Synchronisation man Page Items
- The pvm_freezegroup makes a dynamic group static.
- The group information is then “cached” by all group members.
- A typical call:
int info = pvm_freezegroup(char *group, int count);
group is the name of the group, a C string.count indicates the size the dynamic group should be when made staticpvm_freezegroup is a synchronizing routine and must be called by all group members to complete.- Freezing a group makes certain group operations more efficient.
PVM Synchronisation man Page Items
- The pvm_barrier blocks the calling process until the specified number of processes in the group have called it.
- A typical call:
int info = pvm_barrier(char *group, int count);
group is the name of the group, a C string.- The group must exist and the calling process must be a member of the group.
count specifies the number of group members that must call pvm_barrier before they are all released.
PVM Synchronisation man Page Items
- Though not required, count is expected to be the total number of members of the specified group.
- If info is negative, an error occurred.
- The count argument is required because processes could be joining the given group after other processes have called pvm_barrier.
- An example use:
inum = pvm_barrier("Mitch's Big BAD Group", 43);
PVM Synchronisation man Page Items
- The pvm_lvgroup call unenrolls the calling process from a named group.
- A typical call:
int info = pvm_lvgroup(char *group);
- group is the name of the group.
- info is 0 if successful, negative if an error occurred.
- If a process leaves a group by calling either
pvm_lvgroup or pvm_exit, and later rejoins the same group, the process may be assigned a new instance number.
- Old instance numbers are reassigned to processes calling
pvm_joingroup.
info = pvm_lvgroup("Any group that would have me as a member!" );
PVM Synchronisation man Page Items
- The pvm_gettid call returns the tid of the process identified by a group name and instance number.
- A typical call:
int tid = pvm_gettid(char *group, int inum);
group is the name of the group.
fool = pvm_gettid("Any group that would have me as a member!", 0);
Summary
- Synchronization in PVM
- Single Program Multiple Data Paradigm
- PVM Synchronisation
man Page Items
class: middle, center, inverse
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Reading