[GN] Configure a pool for copy_bundle_data and compile_xcassets tools.

build/toolchain/mac/BUILD.gn

Index: build/toolchain/mac/BUILD.gn
diff --git a/build/toolchain/mac/BUILD.gn b/build/toolchain/mac/BUILD.gn
index 82eacab28eba0fb0596b1ec649ae3dc20ee422c0..442af823f6742afc353e7fd9d4cc8fa89ec995b2 100644
--- a/build/toolchain/mac/BUILD.gn
+++ b/build/toolchain/mac/BUILD.gn
@@ -21,6 +21,15 @@ if (use_goma) {
   goma_prefix = ""
 }
 
+if (current_toolchain == default_toolchain) {
+  # Reduce the number of tasks using the copy_bundle_data and compile_xcassets
+  # tools as they can cause lots of I/O contention when invoking ninja with a
+  # large number of parallel jobs (e.g. when using distributed build like goma).
+  pool("bundle_pool") {
+    depth = 20

[Dirk Pranke, 2016/05/31 22:29:44]

Your desktop machine is probably a lot beefier than the bots, so this is
probably too high by default. It's probably better to re-use the
get_concurrent_links.py script to get default values (see, e.g.,
gcc_toolchain.gni).

You might also want this to be a declare_arg() so that we can tune this on bots
as needed.

... which made me just realize that the mac and ios toolchains aren't using
get_concurrent_links.py either, which is probably bad.

[sdefresne, 2016/06/01 08:22:29]

Done.

+  }
+}
+
 # This will copy the gyp-mac-tool to the build directory. We pass in the source
 # file of the mac tool.
 gyp_mac_tool_source =
@@ -242,6 +251,7 @@ template("mac_toolchain") {
                           root_build_dir)
       command = "python $_tool {{source}} {{output}}"
       description = "COPY_BUNDLE_DATA {{source}} {{output}}"
+      pool = ":bundle_pool($default_toolchain)"
     }
     tool("compile_xcassets") {
       if (is_ios) {
@@ -264,6 +274,7 @@ template("mac_toolchain") {
                 "env $_compile_xcassets_env ./gyp-mac-tool compile-xcassets " +
                 "{} {{inputs}}"
       description = "COMPILE_XCASSETS {{output}}"
+      pool = ":bundle_pool($default_toolchain)"
     }
 
     toolchain_args() {