--- /dev/null
+# Copyright 2015 Google Inc. All rights reserved
+#
+# 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.
+
+# Find source file location from path to this Makefile
+MAKEPARALLEL_SRC_PATH := $(patsubst %/,%,$(dir $(lastword $(MAKEFILE_LIST))))
+ifndef MAKEPARALLEL_SRC_PATH
+ MAKEPARALLEL_SRC_PATH := .
+endif
+
+# Set defaults if they weren't set by the including Makefile
+MAKEPARALLEL_CXX ?= $(CXX)
+MAKEPARALLEL_LD ?= $(CXX)
+MAKEPARALLEL_INTERMEDIATES_PATH ?= .
+MAKEPARALLEL_BIN_PATH ?= .
+
+MAKEPARALLEL_CXX_SRCS := \
+ makeparallel.cpp
+
+MAKEPARALLEL_CXXFLAGS := -Wall -Werror -MMD -MP
+
+MAKEPARALLEL_CXX_SRCS := $(addprefix $(MAKEPARALLEL_SRC_PATH)/,\
+ $(MAKEPARALLEL_CXX_SRCS))
+
+MAKEPARALLEL_CXX_OBJS := $(patsubst $(MAKEPARALLEL_SRC_PATH)/%.cpp,$(MAKEPARALLEL_INTERMEDIATES_PATH)/%.o,$(MAKEPARALLEL_CXX_SRCS))
+
+MAKEPARALLEL := $(MAKEPARALLEL_BIN_PATH)/makeparallel
+
+ifeq ($(shell uname),Linux)
+MAKEPARALLEL_LIBS := -lrt -lpthread
+endif
+
+# Rule to build makeparallel into MAKEPARALLEL_BIN_PATH
+$(MAKEPARALLEL): $(MAKEPARALLEL_CXX_OBJS)
+ @mkdir -p $(dir $@)
+ $(MAKEPARALLEL_LD) -std=c++11 $(MAKEPARALLEL_CXXFLAGS) -o $@ $^ $(MAKEPARALLEL_LIBS)
+
+# Rule to build source files into object files in MAKEPARALLEL_INTERMEDIATES_PATH
+$(MAKEPARALLEL_CXX_OBJS): $(MAKEPARALLEL_INTERMEDIATES_PATH)/%.o: $(MAKEPARALLEL_SRC_PATH)/%.cpp
+ @mkdir -p $(dir $@)
+ $(MAKEPARALLEL_CXX) -c -std=c++11 $(MAKEPARALLEL_CXXFLAGS) -o $@ $<
+
+makeparallel_clean:
+ rm -rf $(MAKEPARALLEL)
+ rm -rf $(MAKEPARALLEL_INTERMEDIATES_PATH)/*.o
+ rm -rf $(MAKEPARALLEL_INTERMEDIATES_PATH)/*.d
+
+.PHONY: makeparallel_clean
+
+-include $(MAKEPARALLEL_INTERMEDIATES_PATH)/*.d
+
+.PHONY: test
+test: $(MAKEPARALLEL)
+ MAKEFLAGS= $(MAKE) -j1234 -C $(MAKEPARALLEL_SRC_PATH) -f Makefile.test MAKEPARALLEL=$(MAKEPARALLEL) test
--- /dev/null
+<!---
+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)
+```
--- /dev/null
+// 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 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>.
+
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include <string>
+#include <vector>
+
+#ifdef __linux__
+#include <error.h>
+#endif
+
+#ifdef __APPLE__
+#include <err.h>
+#define error(code, eval, fmt, ...) errc(eval, code, fmt, ##__VA_ARGS__)
+// Darwin does not interrupt syscalls by default.
+#define TEMP_FAILURE_RETRY(exp) (exp)
+#endif
+
+// Throw an error if fd is not valid.
+static void CheckFd(int fd) {
+ int ret = fcntl(fd, F_GETFD);
+ if (ret < 0) {
+ if (errno == EBADF) {
+ error(errno, 0, "no jobserver pipe, prefix recipe command with '+'");
+ } else {
+ error(errno, errno, "fnctl failed");
+ }
+ }
+}
+
+// Extract --jobserver-fds= argument from MAKEFLAGS environment variable.
+static int GetJobserver(int* in_fd, int* out_fd) {
+ const char* makeflags_env = getenv("MAKEFLAGS");
+ if (makeflags_env == nullptr) {
+ return false;
+ }
+
+ std::string makeflags = makeflags_env;
+
+ const std::string jobserver_fds_arg = "--jobserver-fds=";
+ size_t start = makeflags.find(jobserver_fds_arg);
+
+ if (start == std::string::npos) {
+ return false;
+ }
+
+ start += jobserver_fds_arg.size();
+
+ std::string::size_type end = makeflags.find(' ', start);
+
+ std::string::size_type len;
+ if (end == std::string::npos) {
+ len = std::string::npos;
+ } else {
+ len = end - start;
+ }
+
+ std::string jobserver_fds = makeflags.substr(start, len);
+
+ if (sscanf(jobserver_fds.c_str(), "%d,%d", in_fd, out_fd) != 2) {
+ return false;
+ }
+
+ CheckFd(*in_fd);
+ CheckFd(*out_fd);
+
+ return true;
+}
+
+// Read a single byte from fd, with timeout in milliseconds. Returns true if
+// a byte was read, false on timeout. Throws away the read value.
+// Non-reentrant, uses timer and signal handler global state, plus static
+// variable to communicate with signal handler.
+//
+// Uses a SIGALRM timer to fire a signal after timeout_ms that will interrupt
+// the read syscall if it hasn't yet completed. If the timer fires before the
+// read the read could block forever, so read from a dup'd fd and close it from
+// the signal handler, which will cause the read to return EBADF if it occurs
+// after the signal.
+// The dup/read/close combo is very similar to the system described to avoid
+// a deadlock between SIGCHLD and read at
+// http://make.mad-scientist.net/papers/jobserver-implementation/
+static bool ReadByteTimeout(int fd, int timeout_ms) {
+ // global variable to communicate with the signal handler
+ static int dup_fd = -1;
+
+ // dup the fd so the signal handler can close it without losing the real one
+ dup_fd = dup(fd);
+ if (dup_fd < 0) {
+ error(errno, errno, "dup failed");
+ }
+
+ // set up a signal handler that closes dup_fd on SIGALRM
+ struct sigaction action = {};
+ action.sa_flags = SA_SIGINFO,
+ action.sa_sigaction = [](int, siginfo_t*, void*) {
+ close(dup_fd);
+ };
+ struct sigaction oldaction = {};
+ int ret = sigaction(SIGALRM, &action, &oldaction);
+ if (ret < 0) {
+ error(errno, errno, "sigaction failed");
+ }
+
+ // queue a SIGALRM after timeout_ms
+ const struct itimerval timeout = {{}, {0, timeout_ms * 1000}};
+ ret = setitimer(ITIMER_REAL, &timeout, NULL);
+ if (ret < 0) {
+ error(errno, errno, "setitimer failed");
+ }
+
+ // start the blocking read
+ char buf;
+ int read_ret = read(dup_fd, &buf, 1);
+ int read_errno = errno;
+
+ // cancel the alarm in case it hasn't fired yet
+ const struct itimerval cancel = {};
+ ret = setitimer(ITIMER_REAL, &cancel, NULL);
+ if (ret < 0) {
+ error(errno, errno, "reset setitimer failed");
+ }
+
+ // remove the signal handler
+ ret = sigaction(SIGALRM, &oldaction, NULL);
+ if (ret < 0) {
+ error(errno, errno, "reset sigaction failed");
+ }
+
+ // clean up the dup'd fd in case the signal never fired
+ close(dup_fd);
+ dup_fd = -1;
+
+ if (read_ret == 0) {
+ error(EXIT_FAILURE, 0, "EOF on jobserver pipe");
+ } else if (read_ret > 0) {
+ return true;
+ } else if (read_errno == EINTR || read_errno == EBADF) {
+ return false;
+ } else {
+ error(read_errno, read_errno, "read failed");
+ }
+ abort();
+}
+
+// Measure the size of the jobserver pool by reading from in_fd until it blocks
+static int GetJobserverTokens(int in_fd) {
+ int tokens = 0;
+ pollfd pollfds[] = {{in_fd, POLLIN, 0}};
+ int ret;
+ while ((ret = TEMP_FAILURE_RETRY(poll(pollfds, 1, 0))) != 0) {
+ if (ret < 0) {
+ error(errno, errno, "poll failed");
+ } else if (pollfds[0].revents != POLLIN) {
+ error(EXIT_FAILURE, 0, "unexpected event %d\n", pollfds[0].revents);
+ }
+
+ // There is probably a job token in the jobserver pipe. There is a chance
+ // another process reads it first, which would cause a blocking read to
+ // block forever (or until another process put a token back in the pipe).
+ // The file descriptor can't be set to O_NONBLOCK as that would affect
+ // all users of the pipe, including the parent make process.
+ // ReadByteTimeout emulates a non-blocking read on a !O_NONBLOCK socket
+ // using a SIGALRM that fires after a short timeout.
+ bool got_token = ReadByteTimeout(in_fd, 10);
+ if (!got_token) {
+ // No more tokens
+ break;
+ } else {
+ tokens++;
+ }
+ }
+
+ // This process implicitly gets a token, so pool size is measured size + 1
+ return tokens;
+}
+
+// Return tokens to the jobserver pool.
+static void PutJobserverTokens(int out_fd, int tokens) {
+ // Return all the tokens to the pipe
+ char buf = '+';
+ for (int i = 0; i < tokens; i++) {
+ int ret = TEMP_FAILURE_RETRY(write(out_fd, &buf, 1));
+ if (ret < 0) {
+ error(errno, errno, "write failed");
+ } else if (ret == 0) {
+ error(EXIT_FAILURE, 0, "EOF on jobserver pipe");
+ }
+ }
+}
+
+int main(int argc, char* argv[]) {
+ int in_fd = -1;
+ int out_fd = -1;
+ int tokens = 0;
+
+ const char* path = argv[1];
+ std::vector<char*> args(&argv[1], &argv[argc]);
+
+ if (GetJobserver(&in_fd, &out_fd)) {
+ fcntl(in_fd, F_SETFD, FD_CLOEXEC);
+ fcntl(out_fd, F_SETFD, FD_CLOEXEC);
+
+ tokens = GetJobserverTokens(in_fd);
+ }
+
+ std::string jarg = "-j" + std::to_string(tokens + 1);
+ args.push_back(strdup(jarg.c_str()));
+ args.push_back(nullptr);
+
+ pid_t pid = fork();
+ if (pid < 0) {
+ error(errno, errno, "fork failed");
+ } else if (pid == 0) {
+ // child
+ int ret = execvp(path, args.data());
+ if (ret < 0) {
+ error(errno, errno, "exec failed");
+ }
+ abort();
+ }
+
+ // parent
+ siginfo_t status = {};
+ int exit_status = 0;
+ int ret = waitid(P_PID, pid, &status, WEXITED);
+ if (ret < 0) {
+ error(errno, errno, "waitpid failed");
+ } else if (status.si_code == CLD_EXITED) {
+ exit_status = status.si_status;
+ } else {
+ exit_status = -(status.si_status);
+ }
+
+ if (tokens > 0) {
+ PutJobserverTokens(out_fd, tokens);
+ }
+ exit(exit_status);
+}
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