upload android base code part3

android/build/make/tools/makeparallel/README.md

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+<!---
+Copyright (C) 2015 The Android Open Source Project
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+-->
+
+makeparallel
+============
+makeparallel communicates with the [GNU make jobserver](http://make.mad-scientist.net/papers/jobserver-implementation/)
+in order claim all available jobs, and then passes the number of jobs
+claimed to a subprocess with `-j<jobs>`.
+
+The number of available jobs is determined by reading tokens from the jobserver
+until a read would block.  If the makeparallel rule is the only one running the
+number of jobs will be the total size of the jobserver pool, i.e. the value
+passed to make with `-j`.  Any jobs running in parallel with with the
+makeparellel rule will reduce the measured value, and thus reduce the
+parallelism available to the subprocess.
+
+To run a multi-thread or multi-process binary inside GNU make using
+makeparallel, add
+```Makefile
+	+makeparallel subprocess arguments
+```
+to a rule.  For example, to wrap ninja in make, use something like:
+```Makefile
+	+makeparallel ninja -f build.ninja
+```
+
+To determine the size of the jobserver pool, add
+```Makefile
+	+makeparallel echo > make.jobs
+```
+to a rule that is guarantee to run alone (i.e. all other rules are either
+dependencies of the makeparallel rule, or the depend on the makeparallel
+rule.  The output file will contain the `-j<num>` flag passed to the parent
+make process, or `-j1` if no flag was found.  Since GNU make will run
+makeparallel during the execution phase, after all variables have been
+set and evaluated, it is not possible to get the output of makeparallel
+into a make variable.  Instead, use a shell substitution to read the output
+file directly in a recipe.  For example:
+```Makefile
+	echo Make was started with $$(cat make.jobs)
+```