1 <!--- 2 Copyright (C) 2015 The Android Open Source Project 3 4 Licensed under the Apache License, Version 2.0 (the "License"); 5 you may not use this file except in compliance with the License. 6 You may obtain a copy of the License at 7 8 http://www.apache.org/licenses/LICENSE-2.0 9 10 Unless required by applicable law or agreed to in writing, software 11 distributed under the License is distributed on an "AS IS" BASIS, 12 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 See the License for the specific language governing permissions and 14 limitations under the License. 15 --> 16 17 makeparallel 18 ============ 19 makeparallel communicates with the [GNU make jobserver](http://make.mad-scientist.net/papers/jobserver-implementation/) 20 in order claim all available jobs, and then passes the number of jobs 21 claimed to a subprocess with `-j<jobs>`. 22 23 The number of available jobs is determined by reading tokens from the jobserver 24 until a read would block. If the makeparallel rule is the only one running the 25 number of jobs will be the total size of the jobserver pool, i.e. the value 26 passed to make with `-j`. Any jobs running in parallel with with the 27 makeparellel rule will reduce the measured value, and thus reduce the 28 parallelism available to the subprocess. 29 30 To run a multi-thread or multi-process binary inside GNU make using 31 makeparallel, add 32 ```Makefile 33 +makeparallel subprocess arguments 34 ``` 35 to a rule. For example, to wrap ninja in make, use something like: 36 ```Makefile 37 +makeparallel ninja -f build.ninja 38 ``` 39 40 To determine the size of the jobserver pool, add 41 ```Makefile 42 +makeparallel echo > make.jobs 43 ``` 44 to a rule that is guarantee to run alone (i.e. all other rules are either 45 dependencies of the makeparallel rule, or the depend on the makeparallel 46 rule. The output file will contain the `-j<num>` flag passed to the parent 47 make process, or `-j1` if no flag was found. Since GNU make will run 48 makeparallel during the execution phase, after all variables have been 49 set and evaluated, it is not possible to get the output of makeparallel 50 into a make variable. Instead, use a shell substitution to read the output 51 file directly in a recipe. For example: 52 ```Makefile 53 echo Make was started with $$(cat make.jobs) 54 ``` 55
