Re: [PATCH v2 06/11] commit-graph: simplify chunk writes into loop

From: René Scharfe <l.s.r@web.de>
Date: Jun 25, 2020, 07:25 UTC
Message-ID: <675f46df-c57c-bcd6-3f6a-fdd40b2f3066@web.de>
In-Reply-To: <8b959f2f374654aeb87b847560761890c2f9aa2c.1592934430.git.gitgitgadget@gmail.com>

Am 23.06.20 um 19:47 schrieb SZEDER Gábor via GitGitGadget:

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> From: =?UTF-8?q?SZEDER=20G=C3=A1bor?= <szeder.dev@gmail.com>
>
> In write_commit_graph_file() we now have one block of code filling the
> array of 'struct chunk_info' with the IDs and sizes of chunks to be
> written, and an other block of code calling the functions responsible
> for writing individual chunks.  In case of optional chunks like Extra
> Edge List an Base Graphs List there is also a condition checking
> whether that chunk is necessary/desired, and that same condition is
> repeated in both blocks of code. Other, newer chunks have similar
> optional conditions.
>
> Eliminate these repeated conditions by storing the function pointers
> responsible for writing individual chunks in the 'struct chunk_info'
> array as well, and calling them in a loop to write the commit-graph
> file.  This will open up the possibility for a bit of foolproofing in
> the following patch.

You can do that without storing function pointers by selecting the function to use based on the chunk ID -- like parse_commit_graph() does on the read side. Advantage: You don't need to press all write functions into the same mold and can keep their individual signatures.

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>
> Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> ---
>  commit-graph.c | 31 +++++++++++++++++++------------
>  1 file changed, 19 insertions(+), 12 deletions(-)
>
> diff --git a/commit-graph.c b/commit-graph.c
> index f33bfe49b3..086fc2d070 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -1555,9 +1555,13 @@ static int write_graph_chunk_base(struct hashfile *f,
>  	return 0;
>  }
>
> +typedef int (*chunk_write_fn)(struct hashfile *f,
> +			      struct write_commit_graph_context *ctx);
> +
>  struct chunk_info {
>  	uint32_t id;
>  	uint64_t size;
> +	chunk_write_fn write_fn;
>  };
>
>  static int write_commit_graph_file(struct write_commit_graph_context *ctx)
> @@ -1615,27 +1619,34 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
>
>  	chunks[0].id = GRAPH_CHUNKID_OIDFANOUT;
>  	chunks[0].size = GRAPH_FANOUT_SIZE;
> +	chunks[0].write_fn = write_graph_chunk_fanout;
>  	chunks[1].id = GRAPH_CHUNKID_OIDLOOKUP;
>  	chunks[1].size = hashsz * ctx->commits.nr;
> +	chunks[1].write_fn = write_graph_chunk_oids;
>  	chunks[2].id = GRAPH_CHUNKID_DATA;
>  	chunks[2].size = (hashsz + 16) * ctx->commits.nr;
> +	chunks[2].write_fn = write_graph_chunk_data;
>  	if (ctx->num_extra_edges) {
>  		chunks[num_chunks].id = GRAPH_CHUNKID_EXTRAEDGES;
>  		chunks[num_chunks].size = 4 * ctx->num_extra_edges;
> +		chunks[num_chunks].write_fn = write_graph_chunk_extra_edges;
>  		num_chunks++;
>  	}
>  	if (ctx->changed_paths) {
>  		chunks[num_chunks].id = GRAPH_CHUNKID_BLOOMINDEXES;
>  		chunks[num_chunks].size = sizeof(uint32_t) * ctx->commits.nr;
> +		chunks[num_chunks].write_fn = write_graph_chunk_bloom_indexes;
>  		num_chunks++;
>  		chunks[num_chunks].id = GRAPH_CHUNKID_BLOOMDATA;
>  		chunks[num_chunks].size = sizeof(uint32_t) * 3
>  					  + ctx->total_bloom_filter_data_size;
> +		chunks[num_chunks].write_fn = write_graph_chunk_bloom_data;
>  		num_chunks++;
>  	}
>  	if (ctx->num_commit_graphs_after > 1) {
>  		chunks[num_chunks].id = GRAPH_CHUNKID_BASE;
>  		chunks[num_chunks].size = hashsz * (ctx->num_commit_graphs_after - 1);
> +		chunks[num_chunks].write_fn = write_graph_chunk_base;
>  		num_chunks++;
>  	}
>
> @@ -1671,19 +1682,15 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
>  			progress_title.buf,
>  			num_chunks * ctx->commits.nr);
>  	}
> -	write_graph_chunk_fanout(f, ctx);
> -	write_graph_chunk_oids(f, ctx);
> -	write_graph_chunk_data(f, ctx);
> -	if (ctx->num_extra_edges)
> -		write_graph_chunk_extra_edges(f, ctx);
> -	if (ctx->changed_paths) {
> -		write_graph_chunk_bloom_indexes(f, ctx);
> -		write_graph_chunk_bloom_data(f, ctx);
> -	}
> -	if (ctx->num_commit_graphs_after > 1 &&
> -	    write_graph_chunk_base(f, ctx)) {
> -		return -1;
> +
> +	for (i = 0; i < num_chunks; i++) {
> +		if (chunks[i].write_fn(f, ctx)) {
> +			error(_("failed writing chunk with id %"PRIx32""),
> +			      chunks[i].id);

Of all the write functions only write_graph_chunk_base() can return non-zero and it already prints an error message in that case ("failed to write correct number of base graph ids"). Why add this one?

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> +			return -1;
> +		}
>  	}
> +
>  	stop_progress(&ctx->progress);
>  	strbuf_release(&progress_title);
>
>