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