| Message ID | a3383042e2ee6c454e024db7a9154dc979a5af9e.1616015337.git.matheus.bernardino@usp.br (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Parallel Checkout (part 2) | expand |
On Wed, Mar 17, 2021 at 10:12 PM Matheus Tavares <matheus.bernardino@usp.br> wrote: > +struct parallel_checkout_item { > + /* pointer to a istate->cache[] entry. Not owned by us. */ > + struct cache_entry *ce; > + struct conv_attrs ca; > + struct stat st; > + enum pc_item_status status; > +}; > + > +struct parallel_checkout { > + enum pc_status status; > + struct parallel_checkout_item *items; > + size_t nr, alloc; > +}; It looks like this struct parallel_checkout contains what is called the parallel checkout queue in many places. It would be a bit better if a name or at least a comment could make that clear. > +static struct parallel_checkout parallel_checkout; [...] > +static void finish_parallel_checkout(void) > +{ > + if (parallel_checkout.status == PC_UNINITIALIZED) > + BUG("cannot finish parallel checkout: not initialized yet"); > + > + free(parallel_checkout.items); Ok, it looks like the queue can indeed be freed like this as the items don't need their fields to be freed. > + memset(¶llel_checkout, 0, sizeof(parallel_checkout)); That should work to reset it. > +} > + > +static int is_eligible_for_parallel_checkout(const struct cache_entry *ce, > + const struct conv_attrs *ca) > +{ > + enum conv_attrs_classification c; > + > + /* > + * Symlinks cannot be checked out in parallel as, in case of path > + * collision, they could racily replace leading directories of other > + * entries being checked out. Submodules are checked out in child > + * processes, which have their own parallel checkout queues. > + */ > + if (!S_ISREG(ce->ce_mode)) > + return 0; > + > + c = classify_conv_attrs(ca); > + switch (c) { > + case CA_CLASS_INCORE: > + return 1; > + > + case CA_CLASS_INCORE_FILTER: > + /* > + * It would be safe to allow concurrent instances of > + * single-file smudge filters, like rot13, but we should not > + * assume that all filters are parallel-process safe. So we > + * don't allow this. > + */ > + return 0; > + > + case CA_CLASS_INCORE_PROCESS: > + /* > + * The parallel queue and the delayed queue are not compatible, > + * so they must be kept completely separated. And we can't tell > + * if a long-running process will delay its response without > + * actually asking it to perform the filtering. Therefore, this > + * type of filter is not allowed in parallel checkout. > + * > + * Furthermore, there should only be one instance of the > + * long-running process filter as we don't know how it is > + * managing its own concurrency. So, spreading the entries that > + * requisite such a filter among the parallel workers would > + * require a lot more inter-process communication. We would > + * probably have to designate a single process to interact with > + * the filter and send all the necessary data to it, for each > + * entry. > + */ > + return 0; So it looks like we don't process entries that need filtering. It's a bit disappointing as the commit message says: "This new interface allows us to enqueue some of the entries being checked out to later uncompress, smudge, and write them in parallel." So it seems to say that entries could be smudged in parallel. Or maybe I am missing something? > + case CA_CLASS_STREAMABLE: > + return 1; > + > + default: > + BUG("unsupported conv_attrs classification '%d'", c); > + } > +} [...] > +static int handle_results(struct checkout *state) > +{ > + int ret = 0; > + size_t i; > + int have_pending = 0; > + > + /* > + * We first update the successfully written entries with the collected > + * stat() data, so that they can be found by mark_colliding_entries(), > + * in the next loop, when necessary. > + */ > + for (i = 0; i < parallel_checkout.nr; i++) { > + struct parallel_checkout_item *pc_item = ¶llel_checkout.items[i]; > + if (pc_item->status == PC_ITEM_WRITTEN) > + update_ce_after_write(state, pc_item->ce, &pc_item->st); > + } > + > + for (i = 0; i < parallel_checkout.nr; i++) { > + struct parallel_checkout_item *pc_item = ¶llel_checkout.items[i]; > + > + switch(pc_item->status) { > + case PC_ITEM_WRITTEN: > + /* Already handled */ > + break; > + case PC_ITEM_COLLIDED: > + /* > + * The entry could not be checked out due to a path > + * collision with another entry. Since there can only > + * be one entry of each colliding group on the disk, we > + * could skip trying to check out this one and move on. > + * However, this would leave the unwritten entries with > + * null stat() fields on the index, which could > + * potentially slow down subsequent operations that > + * require refreshing it: git would not be able to > + * trust st_size and would have to go to the filesystem > + * to see if the contents match (see ie_modified()). > + * > + * Instead, let's pay the overhead only once, now, and > + * call checkout_entry_ca() again for this file, to > + * have it's stat() data stored in the index. This also s/it's/its/ > + * has the benefit of adding this entry and its > + * colliding pair to the collision report message. > + * Additionally, this overwriting behavior is consistent > + * with what the sequential checkout does, so it doesn't > + * add any extra overhead. > + */ > + ret |= checkout_entry_ca(pc_item->ce, &pc_item->ca, > + state, NULL, NULL); > + break; > + case PC_ITEM_PENDING: > + have_pending = 1; > + /* fall through */ > + case PC_ITEM_FAILED: > + ret = -1; > + break; > + default: > + BUG("unknown checkout item status in parallel checkout"); > + } > + } > + > + if (have_pending) > + error(_("parallel checkout finished with pending entries")); Is this an error that can actually happen? Or is it a bug? If this can actually happen what is the state of the working directory and what can the user do? Start another checkout with an option to do it sequentially? > + return ret; > +} [...] > +static int write_pc_item_to_fd(struct parallel_checkout_item *pc_item, int fd, > + const char *path) > +{ > + int ret; > + struct stream_filter *filter; > + struct strbuf buf = STRBUF_INIT; > + char *new_blob; > + unsigned long size; I thought that we shouldn't use unsigned long anymore for sizes, but unfortunately it looks like that's what read_blob_entry() expects. > + size_t newsize = 0; I don't think we need to initialize newsize. Also we could perhaps declare it closer to where it is used below. > + ssize_t wrote; > + > + /* Sanity check */ > + assert(is_eligible_for_parallel_checkout(pc_item->ce, &pc_item->ca)); > + > + filter = get_stream_filter_ca(&pc_item->ca, &pc_item->ce->oid); > + if (filter) { > + if (stream_blob_to_fd(fd, &pc_item->ce->oid, filter, 1)) { > + /* On error, reset fd to try writing without streaming */ > + if (reset_fd(fd, path)) > + return -1; > + } else { > + return 0; > + } > + } > + > + new_blob = read_blob_entry(pc_item->ce, &size); > + if (!new_blob) > + return error("unable to read sha1 file of %s (%s)", path, With the support of sha256, I guess we should avoid talking about sha1. Maybe: s/sha1/object/ Or maybe we could just say that we couldn't read the object, as read_blob_entry() would perhaps read it from a pack-file and not from a loose file? > + oid_to_hex(&pc_item->ce->oid)); > + > + /* > + * checkout metadata is used to give context for external process > + * filters. Files requiring such filters are not eligible for parallel > + * checkout, so pass NULL. > + */ > + ret = convert_to_working_tree_ca(&pc_item->ca, pc_item->ce->name, > + new_blob, size, &buf, NULL); > + > + if (ret) { > + free(new_blob); > + new_blob = strbuf_detach(&buf, &newsize); > + size = newsize; "newsize" seems to be used only here. It would be nice if we could get rid of it and pass "&size" to strbuf_detach(), but maybe we cannot because of the unsigned long/size_t type mismatch. At least we could declare "newsize" in this scope though. > + } > + > + wrote = write_in_full(fd, new_blob, size); > + free(new_blob); > + if (wrote < 0) > + return error("unable to write file %s", path); > + > + return 0; > +} > + [...] > +static void write_pc_item(struct parallel_checkout_item *pc_item, > + struct checkout *state) > +{ > + unsigned int mode = (pc_item->ce->ce_mode & 0100) ? 0777 : 0666; It looks like we are using similar code in different places, so it's probably ok, but maybe it would be nice one day to use a macro or an inline function for this. > + int fd = -1, fstat_done = 0; > + struct strbuf path = STRBUF_INIT; > + const char *dir_sep;
On Wed, Mar 31, 2021 at 1:22 AM Christian Couder <christian.couder@gmail.com> wrote: > > On Wed, Mar 17, 2021 at 10:12 PM Matheus Tavares > <matheus.bernardino@usp.br> wrote: > > > +struct parallel_checkout_item { > > + /* pointer to a istate->cache[] entry. Not owned by us. */ > > + struct cache_entry *ce; > > + struct conv_attrs ca; > > + struct stat st; > > + enum pc_item_status status; > > +}; > > + > > +struct parallel_checkout { > > + enum pc_status status; > > + struct parallel_checkout_item *items; > > + size_t nr, alloc; > > +}; > > It looks like this struct parallel_checkout contains what is called > the parallel checkout queue in many places. It would be a bit better > if a name or at least a comment could make that clear. Right, will do. > > + case CA_CLASS_INCORE_PROCESS: > > + /* > > + * The parallel queue and the delayed queue are not compatible, > > + * so they must be kept completely separated. And we can't tell > > + * if a long-running process will delay its response without > > + * actually asking it to perform the filtering. Therefore, this > > + * type of filter is not allowed in parallel checkout. > > + * > > + * Furthermore, there should only be one instance of the > > + * long-running process filter as we don't know how it is > > + * managing its own concurrency. So, spreading the entries that > > + * requisite such a filter among the parallel workers would > > + * require a lot more inter-process communication. We would > > + * probably have to designate a single process to interact with > > + * the filter and send all the necessary data to it, for each > > + * entry. > > + */ > > + return 0; > > So it looks like we don't process entries that need filtering. It's a > bit disappointing as the commit message says: > > "This new interface allows us to enqueue some of the entries being > checked out to later uncompress, smudge, and write them in parallel." > > So it seems to say that entries could be smudged in parallel. Or maybe > I am missing something? Good point, this part of the commit message is indeed misleading. Only internal filters, like re-encoding and end-of-line conversions, can be performed in parallel. I'll rephrase that sentence, thanks! > > +static int handle_results(struct checkout *state) [...] > > + > > + if (have_pending) > > + error(_("parallel checkout finished with pending entries")); > > Is this an error that can actually happen? Or is it a bug? If this can > actually happen what is the state of the working directory [...] ? This could happen both due to a bug or due to an actual error, e.g. if one of the workers die()s or gets killed before finishing its work queue. In these cases, the files associated with the unfinished items will be missing from the working tree, and their index entries will have null stat() information. > [...] and what > can the user do? Start another checkout with an option to do it > sequentially? Hmm, it depends on what caused the error. For example, if the user accidentally killed one of the workers, starting another checkout (either parallel or sequential) should be able to create the missing files. But that might not be the case if the error was caused by a fatal condition in one of the workers which led it to die() (like a packet write failure or corrupted object). Nevertheless, I think it might be interesting to rephrase the error message here to be more explicit about the outcome state. Perhaps even mention how many entries will be missing. > [...] > > > +static int write_pc_item_to_fd(struct parallel_checkout_item *pc_item, int fd, > > + const char *path) > > +{ > > + int ret; > > + struct stream_filter *filter; > > + struct strbuf buf = STRBUF_INIT; > > + char *new_blob; > > + unsigned long size; > > I thought that we shouldn't use unsigned long anymore for sizes, but > unfortunately it looks like that's what read_blob_entry() expects. > > > + size_t newsize = 0; > > I don't think we need to initialize newsize. Also we could perhaps > declare it closer to where it is used below. > > > + ssize_t wrote; > > + > > + /* Sanity check */ > > + assert(is_eligible_for_parallel_checkout(pc_item->ce, &pc_item->ca)); > > + > > + filter = get_stream_filter_ca(&pc_item->ca, &pc_item->ce->oid); > > + if (filter) { > > + if (stream_blob_to_fd(fd, &pc_item->ce->oid, filter, 1)) { > > + /* On error, reset fd to try writing without streaming */ > > + if (reset_fd(fd, path)) > > + return -1; > > + } else { > > + return 0; > > + } > > + } > > + > > + new_blob = read_blob_entry(pc_item->ce, &size); > > + if (!new_blob) > > + return error("unable to read sha1 file of %s (%s)", path, > > With the support of sha256, I guess we should avoid talking about > sha1. Maybe: s/sha1/object/ Or maybe we could just say that we > couldn't read the object, as read_blob_entry() would perhaps read it > from a pack-file and not from a loose file? Good point, thanks! > > + oid_to_hex(&pc_item->ce->oid)); > > + > > + /* > > + * checkout metadata is used to give context for external process > > + * filters. Files requiring such filters are not eligible for parallel > > + * checkout, so pass NULL. > > + */ > > + ret = convert_to_working_tree_ca(&pc_item->ca, pc_item->ce->name, > > + new_blob, size, &buf, NULL); > > + > > + if (ret) { > > + free(new_blob); > > + new_blob = strbuf_detach(&buf, &newsize); > > + size = newsize; > > "newsize" seems to be used only here. It would be nice if we could get > rid of it and pass "&size" to strbuf_detach(), but maybe we cannot > because of the unsigned long/size_t type mismatch. At least we could > declare "newsize" in this scope though. Sure, I'll move "newsize" down to this block and remove the initialization, thanks.
diff --git a/Makefile b/Makefile index dfb0f1000f..f7b9ab49f9 100644 --- a/Makefile +++ b/Makefile @@ -938,6 +938,7 @@ LIB_OBJS += pack-revindex.o LIB_OBJS += pack-write.o LIB_OBJS += packfile.o LIB_OBJS += pager.o +LIB_OBJS += parallel-checkout.o LIB_OBJS += parse-options-cb.o LIB_OBJS += parse-options.o LIB_OBJS += patch-delta.o diff --git a/entry.c b/entry.c index 2ce16414a7..6a22c45050 100644 --- a/entry.c +++ b/entry.c @@ -7,6 +7,7 @@ #include "progress.h" #include "fsmonitor.h" #include "entry.h" +#include "parallel-checkout.h" static void create_directories(const char *path, int path_len, const struct checkout *state) @@ -426,8 +427,17 @@ static void mark_colliding_entries(const struct checkout *state, for (i = 0; i < state->istate->cache_nr; i++) { struct cache_entry *dup = state->istate->cache[i]; - if (dup == ce) - break; + if (dup == ce) { + /* + * Parallel checkout doesn't create the files in index + * order. So the other side of the collision may appear + * after the given cache_entry in the array. + */ + if (parallel_checkout_status() == PC_RUNNING) + continue; + else + break; + } if (dup->ce_flags & (CE_MATCHED | CE_VALID | CE_SKIP_WORKTREE)) continue; @@ -536,6 +546,9 @@ int checkout_entry_ca(struct cache_entry *ce, struct conv_attrs *ca, ca = &ca_buf; } + if (!enqueue_checkout(ce, ca)) + return 0; + return write_entry(ce, path.buf, ca, state, 0); } diff --git a/parallel-checkout.c b/parallel-checkout.c new file mode 100644 index 0000000000..80a60eb2d3 --- /dev/null +++ b/parallel-checkout.c @@ -0,0 +1,368 @@ +#include "cache.h" +#include "entry.h" +#include "parallel-checkout.h" +#include "streaming.h" + +enum pc_item_status { + PC_ITEM_PENDING = 0, + PC_ITEM_WRITTEN, + /* + * The entry could not be written because there was another file + * already present in its path or leading directories. Since + * checkout_entry_ca() removes such files from the working tree before + * enqueueing the entry for parallel checkout, it means that there was + * a path collision among the entries being written. + */ + PC_ITEM_COLLIDED, + PC_ITEM_FAILED, +}; + +struct parallel_checkout_item { + /* pointer to a istate->cache[] entry. Not owned by us. */ + struct cache_entry *ce; + struct conv_attrs ca; + struct stat st; + enum pc_item_status status; +}; + +struct parallel_checkout { + enum pc_status status; + struct parallel_checkout_item *items; + size_t nr, alloc; +}; + +static struct parallel_checkout parallel_checkout; + +enum pc_status parallel_checkout_status(void) +{ + return parallel_checkout.status; +} + +void init_parallel_checkout(void) +{ + if (parallel_checkout.status != PC_UNINITIALIZED) + BUG("parallel checkout already initialized"); + + parallel_checkout.status = PC_ACCEPTING_ENTRIES; +} + +static void finish_parallel_checkout(void) +{ + if (parallel_checkout.status == PC_UNINITIALIZED) + BUG("cannot finish parallel checkout: not initialized yet"); + + free(parallel_checkout.items); + memset(¶llel_checkout, 0, sizeof(parallel_checkout)); +} + +static int is_eligible_for_parallel_checkout(const struct cache_entry *ce, + const struct conv_attrs *ca) +{ + enum conv_attrs_classification c; + + /* + * Symlinks cannot be checked out in parallel as, in case of path + * collision, they could racily replace leading directories of other + * entries being checked out. Submodules are checked out in child + * processes, which have their own parallel checkout queues. + */ + if (!S_ISREG(ce->ce_mode)) + return 0; + + c = classify_conv_attrs(ca); + switch (c) { + case CA_CLASS_INCORE: + return 1; + + case CA_CLASS_INCORE_FILTER: + /* + * It would be safe to allow concurrent instances of + * single-file smudge filters, like rot13, but we should not + * assume that all filters are parallel-process safe. So we + * don't allow this. + */ + return 0; + + case CA_CLASS_INCORE_PROCESS: + /* + * The parallel queue and the delayed queue are not compatible, + * so they must be kept completely separated. And we can't tell + * if a long-running process will delay its response without + * actually asking it to perform the filtering. Therefore, this + * type of filter is not allowed in parallel checkout. + * + * Furthermore, there should only be one instance of the + * long-running process filter as we don't know how it is + * managing its own concurrency. So, spreading the entries that + * requisite such a filter among the parallel workers would + * require a lot more inter-process communication. We would + * probably have to designate a single process to interact with + * the filter and send all the necessary data to it, for each + * entry. + */ + return 0; + + case CA_CLASS_STREAMABLE: + return 1; + + default: + BUG("unsupported conv_attrs classification '%d'", c); + } +} + +int enqueue_checkout(struct cache_entry *ce, struct conv_attrs *ca) +{ + struct parallel_checkout_item *pc_item; + + if (parallel_checkout.status != PC_ACCEPTING_ENTRIES || + !is_eligible_for_parallel_checkout(ce, ca)) + return -1; + + ALLOC_GROW(parallel_checkout.items, parallel_checkout.nr + 1, + parallel_checkout.alloc); + + pc_item = ¶llel_checkout.items[parallel_checkout.nr++]; + pc_item->ce = ce; + memcpy(&pc_item->ca, ca, sizeof(pc_item->ca)); + pc_item->status = PC_ITEM_PENDING; + + return 0; +} + +static int handle_results(struct checkout *state) +{ + int ret = 0; + size_t i; + int have_pending = 0; + + /* + * We first update the successfully written entries with the collected + * stat() data, so that they can be found by mark_colliding_entries(), + * in the next loop, when necessary. + */ + for (i = 0; i < parallel_checkout.nr; i++) { + struct parallel_checkout_item *pc_item = ¶llel_checkout.items[i]; + if (pc_item->status == PC_ITEM_WRITTEN) + update_ce_after_write(state, pc_item->ce, &pc_item->st); + } + + for (i = 0; i < parallel_checkout.nr; i++) { + struct parallel_checkout_item *pc_item = ¶llel_checkout.items[i]; + + switch(pc_item->status) { + case PC_ITEM_WRITTEN: + /* Already handled */ + break; + case PC_ITEM_COLLIDED: + /* + * The entry could not be checked out due to a path + * collision with another entry. Since there can only + * be one entry of each colliding group on the disk, we + * could skip trying to check out this one and move on. + * However, this would leave the unwritten entries with + * null stat() fields on the index, which could + * potentially slow down subsequent operations that + * require refreshing it: git would not be able to + * trust st_size and would have to go to the filesystem + * to see if the contents match (see ie_modified()). + * + * Instead, let's pay the overhead only once, now, and + * call checkout_entry_ca() again for this file, to + * have it's stat() data stored in the index. This also + * has the benefit of adding this entry and its + * colliding pair to the collision report message. + * Additionally, this overwriting behavior is consistent + * with what the sequential checkout does, so it doesn't + * add any extra overhead. + */ + ret |= checkout_entry_ca(pc_item->ce, &pc_item->ca, + state, NULL, NULL); + break; + case PC_ITEM_PENDING: + have_pending = 1; + /* fall through */ + case PC_ITEM_FAILED: + ret = -1; + break; + default: + BUG("unknown checkout item status in parallel checkout"); + } + } + + if (have_pending) + error(_("parallel checkout finished with pending entries")); + + return ret; +} + +static int reset_fd(int fd, const char *path) +{ + if (lseek(fd, 0, SEEK_SET) != 0) + return error_errno("failed to rewind descriptor of %s", path); + if (ftruncate(fd, 0)) + return error_errno("failed to truncate file %s", path); + return 0; +} + +static int write_pc_item_to_fd(struct parallel_checkout_item *pc_item, int fd, + const char *path) +{ + int ret; + struct stream_filter *filter; + struct strbuf buf = STRBUF_INIT; + char *new_blob; + unsigned long size; + size_t newsize = 0; + ssize_t wrote; + + /* Sanity check */ + assert(is_eligible_for_parallel_checkout(pc_item->ce, &pc_item->ca)); + + filter = get_stream_filter_ca(&pc_item->ca, &pc_item->ce->oid); + if (filter) { + if (stream_blob_to_fd(fd, &pc_item->ce->oid, filter, 1)) { + /* On error, reset fd to try writing without streaming */ + if (reset_fd(fd, path)) + return -1; + } else { + return 0; + } + } + + new_blob = read_blob_entry(pc_item->ce, &size); + if (!new_blob) + return error("unable to read sha1 file of %s (%s)", path, + oid_to_hex(&pc_item->ce->oid)); + + /* + * checkout metadata is used to give context for external process + * filters. Files requiring such filters are not eligible for parallel + * checkout, so pass NULL. + */ + ret = convert_to_working_tree_ca(&pc_item->ca, pc_item->ce->name, + new_blob, size, &buf, NULL); + + if (ret) { + free(new_blob); + new_blob = strbuf_detach(&buf, &newsize); + size = newsize; + } + + wrote = write_in_full(fd, new_blob, size); + free(new_blob); + if (wrote < 0) + return error("unable to write file %s", path); + + return 0; +} + +static int close_and_clear(int *fd) +{ + int ret = 0; + + if (*fd >= 0) { + ret = close(*fd); + *fd = -1; + } + + return ret; +} + +static void write_pc_item(struct parallel_checkout_item *pc_item, + struct checkout *state) +{ + unsigned int mode = (pc_item->ce->ce_mode & 0100) ? 0777 : 0666; + int fd = -1, fstat_done = 0; + struct strbuf path = STRBUF_INIT; + const char *dir_sep; + + strbuf_add(&path, state->base_dir, state->base_dir_len); + strbuf_add(&path, pc_item->ce->name, pc_item->ce->ce_namelen); + + dir_sep = find_last_dir_sep(path.buf); + + /* + * The leading dirs should have been already created by now. But, in + * case of path collisions, one of the dirs could have been replaced by + * a symlink (checked out after we enqueued this entry for parallel + * checkout). Thus, we must check the leading dirs again. + */ + if (dir_sep && !has_dirs_only_path(path.buf, dir_sep - path.buf, + state->base_dir_len)) { + pc_item->status = PC_ITEM_COLLIDED; + goto out; + } + + fd = open(path.buf, O_WRONLY | O_CREAT | O_EXCL, mode); + + if (fd < 0) { + if (errno == EEXIST || errno == EISDIR) { + /* + * Errors which probably represent a path collision. + * Suppress the error message and mark the item to be + * retried later, sequentially. ENOTDIR and ENOENT are + * also interesting, but the above has_dirs_only_path() + * call should have already caught these cases. + */ + pc_item->status = PC_ITEM_COLLIDED; + } else { + error_errno("failed to open file %s", path.buf); + pc_item->status = PC_ITEM_FAILED; + } + goto out; + } + + if (write_pc_item_to_fd(pc_item, fd, path.buf)) { + /* Error was already reported. */ + pc_item->status = PC_ITEM_FAILED; + goto out; + } + + fstat_done = fstat_checkout_output(fd, state, &pc_item->st); + + if (close_and_clear(&fd)) { + error_errno("unable to close file %s", path.buf); + pc_item->status = PC_ITEM_FAILED; + goto out; + } + + if (state->refresh_cache && !fstat_done && lstat(path.buf, &pc_item->st) < 0) { + error_errno("unable to stat just-written file %s", path.buf); + pc_item->status = PC_ITEM_FAILED; + goto out; + } + + pc_item->status = PC_ITEM_WRITTEN; + +out: + /* + * No need to check close() return at this point. Either fd is already + * closed, or we are on an error path. + */ + close_and_clear(&fd); + strbuf_release(&path); +} + +static void write_items_sequentially(struct checkout *state) +{ + size_t i; + + for (i = 0; i < parallel_checkout.nr; i++) + write_pc_item(¶llel_checkout.items[i], state); +} + +int run_parallel_checkout(struct checkout *state) +{ + int ret; + + if (parallel_checkout.status != PC_ACCEPTING_ENTRIES) + BUG("cannot run parallel checkout: uninitialized or already running"); + + parallel_checkout.status = PC_RUNNING; + + write_items_sequentially(state); + ret = handle_results(state); + + finish_parallel_checkout(); + return ret; +} diff --git a/parallel-checkout.h b/parallel-checkout.h new file mode 100644 index 0000000000..4ad2a519b3 --- /dev/null +++ b/parallel-checkout.h @@ -0,0 +1,32 @@ +#ifndef PARALLEL_CHECKOUT_H +#define PARALLEL_CHECKOUT_H + +struct cache_entry; +struct checkout; +struct conv_attrs; + +enum pc_status { + PC_UNINITIALIZED = 0, + PC_ACCEPTING_ENTRIES, + PC_RUNNING, +}; + +enum pc_status parallel_checkout_status(void); + +/* + * Put parallel checkout into the PC_ACCEPTING_ENTRIES state. Should be used + * only when in the PC_UNINITIALIZED state. + */ +void init_parallel_checkout(void); + +/* + * Return -1 if parallel checkout is currently not accepting entries or if the + * entry is not eligible for parallel checkout. Otherwise, enqueue the entry + * for later write and return 0. + */ +int enqueue_checkout(struct cache_entry *ce, struct conv_attrs *ca); + +/* Write all the queued entries, returning 0 on success.*/ +int run_parallel_checkout(struct checkout *state); + +#endif /* PARALLEL_CHECKOUT_H */ diff --git a/unpack-trees.c b/unpack-trees.c index 5b3dd38f8c..b9548de96a 100644 --- a/unpack-trees.c +++ b/unpack-trees.c @@ -17,6 +17,7 @@ #include "object-store.h" #include "promisor-remote.h" #include "entry.h" +#include "parallel-checkout.h" /* * Error messages expected by scripts out of plumbing commands such as @@ -441,7 +442,6 @@ static int check_updates(struct unpack_trees_options *o, if (should_update_submodules()) load_gitmodules_file(index, &state); - enable_delayed_checkout(&state); if (has_promisor_remote()) { /* * Prefetch the objects that are to be checked out in the loop @@ -464,6 +464,9 @@ static int check_updates(struct unpack_trees_options *o, to_fetch.oid, to_fetch.nr); oid_array_clear(&to_fetch); } + + enable_delayed_checkout(&state); + init_parallel_checkout(); for (i = 0; i < index->cache_nr; i++) { struct cache_entry *ce = index->cache[i]; @@ -477,6 +480,7 @@ static int check_updates(struct unpack_trees_options *o, } } stop_progress(&progress); + errs |= run_parallel_checkout(&state); errs |= finish_delayed_checkout(&state, NULL); git_attr_set_direction(GIT_ATTR_CHECKIN);
This new interface allows us to enqueue some of the entries being checked out to later uncompress, smudge, and write them in parallel. For now, the parallel checkout machinery is enabled by default and there is no user configuration, but run_parallel_checkout() just writes the queued entries in sequence (without spawning additional workers). The next patch will actually implement the parallelism and, later, we will make it configurable. Note that, to avoid potential data races, not all entries are eligible for parallel checkout. Also, paths that collide on disk (e.g. case-sensitive paths in case-insensitive file systems), are detected by the parallel checkout code and skipped, so that they can be safely sequentially handled later. The collision detection works like the following: - If the collision was at basename (e.g. 'a/b' and 'a/B'), the framework detects it by looking for EEXIST and EISDIR errors after an open(O_CREAT | O_EXCL) failure. - If the collision was at dirname (e.g. 'a/b' and 'A'), it is detected at the has_dirs_only_path() check, which is done for the leading path of each item in the parallel checkout queue. Both verifications rely on the fact that, before enqueueing an entry for parallel checkout, checkout_entry() makes sure that there is no file at the entry's path and that its leading components are all real directories. So, any later change in these conditions indicates that there was a collision (either between two parallel-eligible entries or between an eligible and an ineligible one). After all parallel-eligible entries have been processed, the collided (and thus, skipped) entries are sequentially fed to checkout_entry() again. This is similar to the way the current code deals with collisions, overwriting the previously checked out entries with the subsequent ones. The only difference is that, since we no longer create the files in the same order that they appear on index, we are not able to determine which of the colliding entries will survive on disk (for the classic code, it is always the last entry). Co-authored-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Co-authored-by: Jeff Hostetler <jeffhost@microsoft.com> Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br> --- Makefile | 1 + entry.c | 17 +- parallel-checkout.c | 368 ++++++++++++++++++++++++++++++++++++++++++++ parallel-checkout.h | 32 ++++ unpack-trees.c | 6 +- 5 files changed, 421 insertions(+), 3 deletions(-) create mode 100644 parallel-checkout.c create mode 100644 parallel-checkout.h