1 files changed, 655 insertions, 0 deletions

diff --git a/parallel-checkout.c b/parallel-checkout.c
new file mode 100644
index 0000000..09e8b10
--- /dev/null
+++ b/parallel-checkout.c
@@ -0,0 +1,655 @@
+#include "cache.h"
+#include "config.h"
+#include "entry.h"
+#include "parallel-checkout.h"
+#include "pkt-line.h"
+#include "progress.h"
+#include "run-command.h"
+#include "sigchain.h"
+#include "streaming.h"
+#include "thread-utils.h"
+
+struct pc_worker {
+	struct child_process cp;
+	size_t next_item_to_complete, nr_items_to_complete;
+};
+
+struct parallel_checkout {
+	enum pc_status status;
+	struct parallel_checkout_item *items; /* The parallel checkout queue. */
+	size_t nr, alloc;
+	struct progress *progress;
+	unsigned int *progress_cnt;
+};
+
+static struct parallel_checkout parallel_checkout;
+
+enum pc_status parallel_checkout_status(void)
+{
+	return parallel_checkout.status;
+}
+
+static const int DEFAULT_THRESHOLD_FOR_PARALLELISM = 100;
+static const int DEFAULT_NUM_WORKERS = 1;
+
+void get_parallel_checkout_configs(int *num_workers, int *threshold)
+{
+	if (git_config_get_int("checkout.workers", num_workers))
+		*num_workers = DEFAULT_NUM_WORKERS;
+	else if (*num_workers < 1)
+		*num_workers = online_cpus();
+
+	if (git_config_get_int("checkout.thresholdForParallelism", threshold))
+		*threshold = DEFAULT_THRESHOLD_FOR_PARALLELISM;
+}
+
+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(&parallel_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;
+	size_t packed_item_size;
+
+	/*
+	 * 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;
+
+	packed_item_size = sizeof(struct pc_item_fixed_portion) + ce->ce_namelen +
+		(ca->working_tree_encoding ? strlen(ca->working_tree_encoding) : 0);
+
+	/*
+	 * The amount of data we send to the workers per checkout item is
+	 * typically small (75~300B). So unless we find an insanely huge path
+	 * of 64KB, we should never reach the 65KB limit of one pkt-line. If
+	 * that does happen, we let the sequential code handle the item.
+	 */
+	if (packed_item_size > LARGE_PACKET_DATA_MAX)
+		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 = &parallel_checkout.items[parallel_checkout.nr];
+	pc_item->ce = ce;
+	memcpy(&pc_item->ca, ca, sizeof(pc_item->ca));
+	pc_item->status = PC_ITEM_PENDING;
+	pc_item->id = parallel_checkout.nr;
+	parallel_checkout.nr++;
+
+	return 0;
+}
+
+size_t pc_queue_size(void)
+{
+	return parallel_checkout.nr;
+}
+
+static void advance_progress_meter(void)
+{
+	if (parallel_checkout.progress) {
+		(*parallel_checkout.progress_cnt)++;
+		display_progress(parallel_checkout.progress,
+				 *parallel_checkout.progress_cnt);
+	}
+}
+
+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 = &parallel_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 = &parallel_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 its 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);
+			advance_progress_meter();
+			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 *blob;
+	unsigned long size;
+	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;
+		}
+	}
+
+	blob = read_blob_entry(pc_item->ce, &size);
+	if (!blob)
+		return error("cannot read object %s '%s'",
+			     oid_to_hex(&pc_item->ce->oid), pc_item->ce->name);
+
+	/*
+	 * checkout metadata is used to give context for external process
+	 * filters. Files requiring such filters are not eligible for parallel
+	 * checkout, so pass NULL. Note: if that changes, the metadata must also
+	 * be passed from the main process to the workers.
+	 */
+	ret = convert_to_working_tree_ca(&pc_item->ca, pc_item->ce->name,
+					 blob, size, &buf, NULL);
+
+	if (ret) {
+		size_t newsize;
+		free(blob);
+		blob = strbuf_detach(&buf, &newsize);
+		size = newsize;
+	}
+
+	wrote = write_in_full(fd, blob, size);
+	free(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;
+}
+
+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;
+		close_and_clear(&fd);
+		unlink(path.buf);
+		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:
+	strbuf_release(&path);
+}
+
+static void send_one_item(int fd, struct parallel_checkout_item *pc_item)
+{
+	size_t len_data;
+	char *data, *variant;
+	struct pc_item_fixed_portion *fixed_portion;
+	const char *working_tree_encoding = pc_item->ca.working_tree_encoding;
+	size_t name_len = pc_item->ce->ce_namelen;
+	size_t working_tree_encoding_len = working_tree_encoding ?
+					   strlen(working_tree_encoding) : 0;
+
+	/*
+	 * Any changes in the calculation of the message size must also be made
+	 * in is_eligible_for_parallel_checkout().
+	 */
+	len_data = sizeof(struct pc_item_fixed_portion) + name_len +
+		   working_tree_encoding_len;
+
+	data = xcalloc(1, len_data);
+
+	fixed_portion = (struct pc_item_fixed_portion *)data;
+	fixed_portion->id = pc_item->id;
+	fixed_portion->ce_mode = pc_item->ce->ce_mode;
+	fixed_portion->crlf_action = pc_item->ca.crlf_action;
+	fixed_portion->ident = pc_item->ca.ident;
+	fixed_portion->name_len = name_len;
+	fixed_portion->working_tree_encoding_len = working_tree_encoding_len;
+	/*
+	 * We use hashcpy() instead of oidcpy() because the hash[] positions
+	 * after `the_hash_algo->rawsz` might not be initialized. And Valgrind
+	 * would complain about passing uninitialized bytes to a syscall
+	 * (write(2)). There is no real harm in this case, but the warning could
+	 * hinder the detection of actual errors.
+	 */
+	hashcpy(fixed_portion->oid.hash, pc_item->ce->oid.hash);
+
+	variant = data + sizeof(*fixed_portion);
+	if (working_tree_encoding_len) {
+		memcpy(variant, working_tree_encoding, working_tree_encoding_len);
+		variant += working_tree_encoding_len;
+	}
+	memcpy(variant, pc_item->ce->name, name_len);
+
+	packet_write(fd, data, len_data);
+
+	free(data);
+}
+
+static void send_batch(int fd, size_t start, size_t nr)
+{
+	size_t i;
+	sigchain_push(SIGPIPE, SIG_IGN);
+	for (i = 0; i < nr; i++)
+		send_one_item(fd, &parallel_checkout.items[start + i]);
+	packet_flush(fd);
+	sigchain_pop(SIGPIPE);
+}
+
+static struct pc_worker *setup_workers(struct checkout *state, int num_workers)
+{
+	struct pc_worker *workers;
+	int i, workers_with_one_extra_item;
+	size_t base_batch_size, batch_beginning = 0;
+
+	ALLOC_ARRAY(workers, num_workers);
+
+	for (i = 0; i < num_workers; i++) {
+		struct child_process *cp = &workers[i].cp;
+
+		child_process_init(cp);
+		cp->git_cmd = 1;
+		cp->in = -1;
+		cp->out = -1;
+		cp->clean_on_exit = 1;
+		strvec_push(&cp->args, "checkout--worker");
+		if (state->base_dir_len)
+			strvec_pushf(&cp->args, "--prefix=%s", state->base_dir);
+		if (start_command(cp))
+			die("failed to spawn checkout worker");
+	}
+
+	base_batch_size = parallel_checkout.nr / num_workers;
+	workers_with_one_extra_item = parallel_checkout.nr % num_workers;
+
+	for (i = 0; i < num_workers; i++) {
+		struct pc_worker *worker = &workers[i];
+		size_t batch_size = base_batch_size;
+
+		/* distribute the extra work evenly */
+		if (i < workers_with_one_extra_item)
+			batch_size++;
+
+		send_batch(worker->cp.in, batch_beginning, batch_size);
+		worker->next_item_to_complete = batch_beginning;
+		worker->nr_items_to_complete = batch_size;
+
+		batch_beginning += batch_size;
+	}
+
+	return workers;
+}
+
+static void finish_workers(struct pc_worker *workers, int num_workers)
+{
+	int i;
+
+	/*
+	 * Close pipes before calling finish_command() to let the workers
+	 * exit asynchronously and avoid spending extra time on wait().
+	 */
+	for (i = 0; i < num_workers; i++) {
+		struct child_process *cp = &workers[i].cp;
+		if (cp->in >= 0)
+			close(cp->in);
+		if (cp->out >= 0)
+			close(cp->out);
+	}
+
+	for (i = 0; i < num_workers; i++) {
+		int rc = finish_command(&workers[i].cp);
+		if (rc > 128) {
+			/*
+			 * For a normal non-zero exit, the worker should have
+			 * already printed something useful to stderr. But a
+			 * death by signal should be mentioned to the user.
+			 */
+			error("checkout worker %d died of signal %d", i, rc - 128);
+		}
+	}
+
+	free(workers);
+}
+
+static inline void assert_pc_item_result_size(int got, int exp)
+{
+	if (got != exp)
+		BUG("wrong result size from checkout worker (got %dB, exp %dB)",
+		    got, exp);
+}
+
+static void parse_and_save_result(const char *buffer, int len,
+				  struct pc_worker *worker)
+{
+	struct pc_item_result *res;
+	struct parallel_checkout_item *pc_item;
+	struct stat *st = NULL;
+
+	if (len < PC_ITEM_RESULT_BASE_SIZE)
+		BUG("too short result from checkout worker (got %dB, exp >=%dB)",
+		    len, (int)PC_ITEM_RESULT_BASE_SIZE);
+
+	res = (struct pc_item_result *)buffer;
+
+	/*
+	 * Worker should send either the full result struct on success, or
+	 * just the base (i.e. no stat data), otherwise.
+	 */
+	if (res->status == PC_ITEM_WRITTEN) {
+		assert_pc_item_result_size(len, (int)sizeof(struct pc_item_result));
+		st = &res->st;
+	} else {
+		assert_pc_item_result_size(len, (int)PC_ITEM_RESULT_BASE_SIZE);
+	}
+
+	if (!worker->nr_items_to_complete)
+		BUG("received result from supposedly finished checkout worker");
+	if (res->id != worker->next_item_to_complete)
+		BUG("unexpected item id from checkout worker (got %"PRIuMAX", exp %"PRIuMAX")",
+		    (uintmax_t)res->id, (uintmax_t)worker->next_item_to_complete);
+
+	worker->next_item_to_complete++;
+	worker->nr_items_to_complete--;
+
+	pc_item = &parallel_checkout.items[res->id];
+	pc_item->status = res->status;
+	if (st)
+		pc_item->st = *st;
+
+	if (res->status != PC_ITEM_COLLIDED)
+		advance_progress_meter();
+}
+
+static void gather_results_from_workers(struct pc_worker *workers,
+					int num_workers)
+{
+	int i, active_workers = num_workers;
+	struct pollfd *pfds;
+
+	CALLOC_ARRAY(pfds, num_workers);
+	for (i = 0; i < num_workers; i++) {
+		pfds[i].fd = workers[i].cp.out;
+		pfds[i].events = POLLIN;
+	}
+
+	while (active_workers) {
+		int nr = poll(pfds, num_workers, -1);
+
+		if (nr < 0) {
+			if (errno == EINTR)
+				continue;
+			die_errno("failed to poll checkout workers");
+		}
+
+		for (i = 0; i < num_workers && nr > 0; i++) {
+			struct pc_worker *worker = &workers[i];
+			struct pollfd *pfd = &pfds[i];
+
+			if (!pfd->revents)
+				continue;
+
+			if (pfd->revents & POLLIN) {
+				int len = packet_read(pfd->fd, NULL, NULL,
+						      packet_buffer,
+						      sizeof(packet_buffer), 0);
+
+				if (len < 0) {
+					BUG("packet_read() returned negative value");
+				} else if (!len) {
+					pfd->fd = -1;
+					active_workers--;
+				} else {
+					parse_and_save_result(packet_buffer,
+							      len, worker);
+				}
+			} else if (pfd->revents & POLLHUP) {
+				pfd->fd = -1;
+				active_workers--;
+			} else if (pfd->revents & (POLLNVAL | POLLERR)) {
+				die("error polling from checkout worker");
+			}
+
+			nr--;
+		}
+	}
+
+	free(pfds);
+}
+
+static void write_items_sequentially(struct checkout *state)
+{
+	size_t i;
+
+	for (i = 0; i < parallel_checkout.nr; i++) {
+		struct parallel_checkout_item *pc_item = &parallel_checkout.items[i];
+		write_pc_item(pc_item, state);
+		if (pc_item->status != PC_ITEM_COLLIDED)
+			advance_progress_meter();
+	}
+}
+
+int run_parallel_checkout(struct checkout *state, int num_workers, int threshold,
+			  struct progress *progress, unsigned int *progress_cnt)
+{
+	int ret;
+
+	if (parallel_checkout.status != PC_ACCEPTING_ENTRIES)
+		BUG("cannot run parallel checkout: uninitialized or already running");
+
+	parallel_checkout.status = PC_RUNNING;
+	parallel_checkout.progress = progress;
+	parallel_checkout.progress_cnt = progress_cnt;
+
+	if (parallel_checkout.nr < num_workers)
+		num_workers = parallel_checkout.nr;
+
+	if (num_workers <= 1 || parallel_checkout.nr < threshold) {
+		write_items_sequentially(state);
+	} else {
+		struct pc_worker *workers = setup_workers(state, num_workers);
+		gather_results_from_workers(workers, num_workers);
+		finish_workers(workers, num_workers);
+	}
+
+	ret = handle_results(state);
+
+	finish_parallel_checkout();
+	return ret;
+}