From 2841e8f81cb2820024804b9341577be1d0ce1240 Mon Sep 17 00:00:00 2001 From: Lars Schneider Date: Fri, 30 Jun 2017 22:41:28 +0200 Subject: convert: add "status=delayed" to filter process protocol Some `clean` / `smudge` filters may require a significant amount of time to process a single blob (e.g. the Git LFS smudge filter might perform network requests). During this process the Git checkout operation is blocked and Git needs to wait until the filter is done to continue with the checkout. Teach the filter process protocol, introduced in edcc8581 ("convert: add filter..process option", 2016-10-16), to accept the status "delayed" as response to a filter request. Upon this response Git continues with the checkout operation. After the checkout operation Git calls "finish_delayed_checkout" which queries the filter for remaining blobs. If the filter is still working on the completion, then the filter is expected to block. If the filter has completed all remaining blobs then an empty response is expected. Git has a multiple code paths that checkout a blob. Support delayed checkouts only in `clone` (in unpack-trees.c) and `checkout` operations for now. The optimization is most effective in these code paths as all files of the tree are processed. Signed-off-by: Lars Schneider Signed-off-by: Junio C Hamano --- Documentation/gitattributes.txt | 69 ++++++++++++++++++++++++++++++++++++++--- 1 file changed, 65 insertions(+), 4 deletions(-) (limited to 'Documentation') diff --git a/Documentation/gitattributes.txt b/Documentation/gitattributes.txt index 4736483865..4049a0b9a8 100644 --- a/Documentation/gitattributes.txt +++ b/Documentation/gitattributes.txt @@ -425,8 +425,8 @@ packet: git< capability=clean packet: git< capability=smudge packet: git< 0000 ------------------------ -Supported filter capabilities in version 2 are "clean" and -"smudge". +Supported filter capabilities in version 2 are "clean", "smudge", +and "delay". Afterwards Git sends a list of "key=value" pairs terminated with a flush packet. The list will contain at least the filter command @@ -512,12 +512,73 @@ the protocol then Git will stop the filter process and restart it with the next file that needs to be processed. Depending on the `filter..required` flag Git will interpret that as error. -After the filter has processed a blob it is expected to wait for -the next "key=value" list containing a command. Git will close +After the filter has processed a command it is expected to wait for +a "key=value" list containing the next command. Git will close the command pipe on exit. The filter is expected to detect EOF and exit gracefully on its own. Git will wait until the filter process has stopped. +Delay +^^^^^ + +If the filter supports the "delay" capability, then Git can send the +flag "can-delay" after the filter command and pathname. This flag +denotes that the filter can delay filtering the current blob (e.g. to +compensate network latencies) by responding with no content but with +the status "delayed" and a flush packet. +------------------------ +packet: git> command=smudge +packet: git> pathname=path/testfile.dat +packet: git> can-delay=1 +packet: git> 0000 +packet: git> CONTENT +packet: git> 0000 +packet: git< status=delayed +packet: git< 0000 +------------------------ + +If the filter supports the "delay" capability then it must support the +"list_available_blobs" command. If Git sends this command, then the +filter is expected to return a list of pathnames representing blobs +that have been delayed earlier and are now available. +The list must be terminated with a flush packet followed +by a "success" status that is also terminated with a flush packet. If +no blobs for the delayed paths are available, yet, then the filter is +expected to block the response until at least one blob becomes +available. The filter can tell Git that it has no more delayed blobs +by sending an empty list. As soon as the filter responds with an empty +list, Git stops asking. All blobs that Git has not received at this +point are considered missing and will result in an error. + +------------------------ +packet: git> command=list_available_blobs +packet: git> 0000 +packet: git< pathname=path/testfile.dat +packet: git< pathname=path/otherfile.dat +packet: git< 0000 +packet: git< status=success +packet: git< 0000 +------------------------ + +After Git received the pathnames, it will request the corresponding +blobs again. These requests contain a pathname and an empty content +section. The filter is expected to respond with the smudged content +in the usual way as explained above. +------------------------ +packet: git> command=smudge +packet: git> pathname=path/testfile.dat +packet: git> 0000 +packet: git> 0000 # empty content! +packet: git< status=success +packet: git< 0000 +packet: git< SMUDGED_CONTENT +packet: git< 0000 +packet: git< 0000 # empty list, keep "status=success" unchanged! +------------------------ + +Example +^^^^^^^ + A long running filter demo implementation can be found in `contrib/long-running-filter/example.pl` located in the Git core repository. If you develop your own long running filter -- cgit v1.2.3