Difference between revisions of "Talk:Transactions"
(→Examples) |
(Processing loop example) |
||
| Line 24: | Line 24: | ||
----------------- | ----------------- | ||
| − | |||
feature<br/> | feature<br/> | ||
incorrect_removal(container: DISPENSER) is<br/> | incorrect_removal(container: DISPENSER) is<br/> | ||
| Line 38: | Line 37: | ||
---------------- | ---------------- | ||
| − | |||
Example of concurrency:<br/> | Example of concurrency:<br/> | ||
feature<br/> | feature<br/> | ||
| Line 52: | Line 50: | ||
---------------- | ---------------- | ||
| − | |||
feature<br/> | feature<br/> | ||
write_file is<br/> | write_file is<br/> | ||
| Line 64: | Line 61: | ||
This is how transactional features can be mapped on to external function calls that support transactional operations | This is how transactional features can be mapped on to external function calls that support transactional operations | ||
---------------- | ---------------- | ||
| + | |||
| + | feature<br/> | ||
| + | source: DISPENSER[ANY] --Where items are taken from | ||
| + | destination: DISPENSER[ANY] -- where items are put after processing | ||
| + | running: BOOLEAN -- Flag to stop processing | ||
| + | |||
| + | consumer is<br/> | ||
| + | do | ||
| + | from | ||
| + | until | ||
| + | not (running) | ||
| + | loop --This loop will spawn multiple threads, microthreads, hyperthreads, or whatever the implementation is and runtime chooses, all processing a single item. | ||
| + | process_single_item | ||
| + | end | ||
| + | end | ||
| + | |||
| + | process_single_item is | ||
| + | local | ||
| + | item: ANY | ||
| + | transaction --Since this is a transaction, accessing the container is safe even when run concurrently. | ||
| + | item := source.item | ||
| + | source.remove | ||
| + | io.put_string(item.to_string) | ||
| + | destination.put(item) | ||
| + | end | ||
Revision as of 10:48, 6 April 2007
Discussion of the feasibility and desirability of implementing transactional concurrency in Eiffel.
Examples please
I think we need to see some examples (well, I do for one).
Examples
The main thing to remember is that the proposal states that all features calls are asynchronous.
Transactions are assured with transactional memory, probably implemented as software transactional memory.
Example of transaction:
feature
correct_removal(container: DISPENSER) is
transaction -- This is a transaction so it is assured to be atomic and isolated
if
not(container.is_empty)
then
container.remove
end
end
This feature is assured to be correct because is is isolated and atomic with respect to the system. If the container has been modified between the call to is_empty and remove, the feature would be aborted and retried.
feature
incorrect_removal(container: DISPENSER) is
do
if
not(container.is_empty)
then
container.remove
end
end
This is the standard example of concurrency issues with preconditions. The container can change between the call to is_empty and remove. Using transactions avoids this.
Example of concurrency:
feature
write_all_files is
do
write_file_1
write_file_2
write_file_3
write_file_4
end
Since all feature calls would be asynchronous, the four write_file features could be executed in parallel if the runtime decides to do so. This is not a transaction so isolation across these calls is not assured.
feature
write_file is
external
"operating_system_write"
abort
"operating_system_abort"
commit
"operating_system_commit"
This is how transactional features can be mapped on to external function calls that support transactional operations
feature
source: DISPENSER[ANY] --Where items are taken from
destination: DISPENSER[ANY] -- where items are put after processing
running: BOOLEAN -- Flag to stop processing
consumer is
do
from
until
not (running)
loop --This loop will spawn multiple threads, microthreads, hyperthreads, or whatever the implementation is and runtime chooses, all processing a single item.
process_single_item
end
end
process_single_item is local item: ANY transaction --Since this is a transaction, accessing the container is safe even when run concurrently. item := source.item source.remove io.put_string(item.to_string) destination.put(item) end
