From: Eric Biggers Date: Sun, 18 Nov 2012 08:13:10 +0000 (-0600) Subject: main_writer_thread_proc(): Add more comments X-Git-Tag: v1.1.0~13 X-Git-Url: https://wimlib.net/git/?p=wimlib;a=commitdiff_plain;h=537248961d441c42f1d4ca63c0efcdb5ceae2193 main_writer_thread_proc(): Add more comments --- diff --git a/src/write.c b/src/write.c index 66635645..56fbab0e 100644 --- a/src/write.c +++ b/src/write.c @@ -498,7 +498,7 @@ finish_wim_resource_chunk_tab(struct chunk_table *chunk_tab, } static int prepare_resource_for_read(struct lookup_table_entry *lte - + #ifdef WITH_NTFS_3G , ntfs_inode **ni_ret #endif @@ -940,6 +940,18 @@ static int write_wim_chunks(struct message *msg, FILE *out_fp, return 0; } +/* + * This function is executed by the main thread when the resources are being + * compressed in parallel. The main thread is in change of all reading of the + * uncompressed data and writing of the compressed data. The compressor threads + * *only* do compression from/to in-memory buffers. + * + * Each unit of work given to a compressor thread is up to MAX_CHUNKS_PER_MSG + * chunks of compressed data to compress, represented in a `struct message'. + * Each message is passed from the main thread to a worker thread through the + * res_to_compress_queue, and it is passed back through the + * compressed_res_queue. + */ static int main_writer_thread_proc(struct list_head *stream_list, FILE *out_fp, int out_ctype, @@ -953,12 +965,27 @@ static int main_writer_thread_proc(struct list_head *stream_list, struct message msgs[queue_size]; ZERO_ARRAY(msgs); + // Initially, all the messages are available to use. LIST_HEAD(available_msgs); - for (size_t i = 0; i < ARRAY_LEN(msgs); i++) list_add(&msgs[i].list, &available_msgs); - + // outstanding_resources is the list of resources that currently have + // had chunks sent off for compression. + // + // The first stream in outstanding_resources is the stream that is + // currently being written (cur_lte). + // + // The last stream in outstanding_resources is the stream that is + // currently being read and chunks fed to the compressor threads + // (next_lte). + // + // Depending on the number of threads and the sizes of the resource, + // the outstanding streams list may contain streams between cur_lte and + // next_lte that have all their chunks compressed or being compressed, + // but haven't been written yet. + // + LIST_HEAD(outstanding_resources); struct list_head *next_resource = stream_list->next; struct lookup_table_entry *next_lte = container_of(next_resource, struct lookup_table_entry, @@ -967,19 +994,17 @@ static int main_writer_thread_proc(struct list_head *stream_list, u64 next_chunk = 0; u64 next_num_chunks = wim_resource_chunks(next_lte); INIT_LIST_HEAD(&next_lte->msg_list); + list_add_tail(&next_lte->staging_list, &outstanding_resources); + + // As in write_wim_resource(), each resource we read is checksummed. SHA_CTX next_sha_ctx; sha1_init(&next_sha_ctx); - u8 next_hash[SHA1_HASH_SIZE]; - // Resources owning chunks that have been sent off for compression - LIST_HEAD(outstanding_resources); - - // Resources that are going to be written by the main thread + // Resources that don't need any chunks compressed are added to this + // list and written directly by the main thread. LIST_HEAD(my_resources); - list_add_tail(&next_lte->staging_list, &outstanding_resources); - struct lookup_table_entry *cur_lte = next_lte; struct chunk_table *cur_chunk_tab = NULL; struct lookup_table_entry *lte; @@ -999,6 +1024,8 @@ static int main_writer_thread_proc(struct list_head *stream_list, "and compressed data (%zu bytes needed)", queue_size * MAX_CHUNKS_PER_MSG * WIM_CHUNK_SIZE * 2); + // Pre-allocate all the buffers that will be needed to do the chunk + // compression. for (size_t i = 0; i < ARRAY_LEN(msgs); i++) { for (size_t j = 0; j < MAX_CHUNKS_PER_MSG; j++) { msgs[i].compressed_chunks[j] = MALLOC(WIM_CHUNK_SIZE); @@ -1021,8 +1048,6 @@ static int main_writer_thread_proc(struct list_head *stream_list, // compressed. while (!list_empty(&available_msgs) && next_lte != NULL) { - wimlib_assert(next_chunk < next_num_chunks); - // Get a message from the available messages // list msg = container_of(available_msgs.next, @@ -1043,12 +1068,18 @@ static int main_writer_thread_proc(struct list_head *stream_list, unsigned size = WIM_CHUNK_SIZE; for (unsigned i = 0; i < msg->num_chunks; i++) { + + // Read chunk @next_chunk of the stream into the + // message so that a compressor thread can + // compress it. + if (next_chunk == next_num_chunks - 1 && wim_resource_size(next_lte) % WIM_CHUNK_SIZE != 0) { size = wim_resource_size(next_lte) % WIM_CHUNK_SIZE; } + DEBUG2("Read resource (size=%u, offset=%zu)", size, next_chunk * WIM_CHUNK_SIZE); @@ -1092,13 +1123,11 @@ static int main_writer_thread_proc(struct list_head *stream_list, // Advance to the next resource. // - // If the next resource needs no compression, - // just write it with this thread (not now - // though--- we could be in the middle of - // writing another resource.) Keep doing this - // until we either get to the end of the - // resources list, or we get to a resource that - // needs compression. + // If the next resource needs no compression, just write + // it with this thread (not now though--- we could be in + // the middle of writing another resource.) Keep doing + // this until we either get to the end of the resources + // list, or we get to a resource that needs compression. while (1) { if (next_resource == stream_list) { @@ -1143,7 +1172,7 @@ static int main_writer_thread_proc(struct list_head *stream_list, } // If there are no outstanding resources, there are no more - // resources to compress. + // resources that need to be written. if (list_empty(&outstanding_resources)) { DEBUG("No outstanding resources! Done"); ret = 0; @@ -1177,16 +1206,13 @@ static int main_writer_thread_proc(struct list_head *stream_list, DEBUG2("Complete msg (begin_chunk=%"PRIu64")", msg->begin_chunk); if (msg->begin_chunk == 0) { DEBUG2("Begin chunk tab"); - // This is the first set of chunks. - // Leave space for the chunk table in - // the output file. + // This is the first set of chunks. Leave space + // for the chunk table in the output file. off_t cur_offset = ftello(out_fp); if (cur_offset == -1) { ret = WIMLIB_ERR_WRITE; goto out; } - FREE(cur_chunk_tab); - cur_chunk_tab = NULL; ret = begin_wim_resource_chunk_tab(cur_lte, out_fp, cur_offset, @@ -1194,13 +1220,20 @@ static int main_writer_thread_proc(struct list_head *stream_list, if (ret != 0) goto out; } + + // Write the compressed chunks from the message. ret = write_wim_chunks(msg, out_fp, cur_chunk_tab); if (ret != 0) goto out; list_del(&msg->list); + + // This message is available to use for different chunks + // now. list_add(&msg->list, &available_msgs); + // Was this the last chunk of the stream? If so, + // finish it. if (list_empty(&cur_lte->msg_list) && msg->begin_chunk + msg->num_chunks == cur_chunk_tab->num_chunks) { @@ -1210,7 +1243,8 @@ static int main_writer_thread_proc(struct list_head *stream_list, out_fp, &res_csize); if (ret != 0) - return ret; + goto out; + cur_lte->output_resource_entry.size = res_csize; @@ -1225,6 +1259,9 @@ static int main_writer_thread_proc(struct list_head *stream_list, cur_lte->resource_entry.flags | WIM_RESHDR_FLAG_COMPRESSED; + FREE(cur_chunk_tab); + cur_chunk_tab = NULL; + struct list_head *next = cur_lte->staging_list.next; list_del(&cur_lte->staging_list); @@ -1238,6 +1275,13 @@ static int main_writer_thread_proc(struct list_head *stream_list, staging_list); } + // Since we just finished writing a stream, + // write any streams that have been added to the + // my_resources list for direct writing by the + // main thread (e.g. resources that don't need + // to be compressed because the desired + // compression type is the same as the previous + // compression type). struct lookup_table_entry *tmp; list_for_each_entry_safe(lte, tmp, @@ -1281,7 +1325,7 @@ out: } while (num_available_msgs < ARRAY_LEN(msgs)) { - msg = shared_queue_get(compressed_res_queue); + shared_queue_get(compressed_res_queue); num_available_msgs++; } } @@ -1333,7 +1377,6 @@ static int write_stream_list_parallel(struct list_head *stream_list, if (ret != 0) goto out_destroy_res_to_compress_queue; - struct compressor_thread_params params; params.res_to_compress_queue = &res_to_compress_queue; params.compressed_res_queue = &compressed_res_queue; @@ -1412,7 +1455,7 @@ static int write_stream_list(struct list_head *stream_list, FILE *out_fp, wimlib_get_compression_type_string(out_ctype)); } - if (compression_needed && total_size >= 0) { // XXX + if (compression_needed && total_size >= 1000000) { return write_stream_list_parallel(stream_list, out_fp, out_ctype, write_flags); } else {