Support for GNU Make jobserver

build.c

@@ -31,11 +31,12 @@ struct job {
 	bool failed;
 };
 
-struct buildoptions buildopts = {.maxfail = 1};
+struct buildoptions buildopts = {.maxfail = 1, .gmakepipe = {-1, -1} };
 static struct edge *work;
 static size_t nstarted, nfinished, ntotal;
 static bool consoleused;
 static struct timespec starttime;
+static char gmaketokens[512], *gmakelatest = gmaketokens;
 
 void
 buildreset(void)
@@ -322,6 +323,15 @@ jobstart(struct job *j, struct edge *e)
 		warn("posix_spawn_file_actions_addclose:");
 		goto err3;
 	}
+	if (buildopts.gmakepipe[0] >= 0) {
+		/* do not allow children to steal GNU/tokens */
+		for (i = 0; i < 2; ++i) {
+			if ((errno = posix_spawn_file_actions_addclose(&actions, buildopts.gmakepipe[i]))) {
+				warn("posix_spawn_file_actions_addclose:");
+				goto err3;
+			}
+		}
+	}
 	if (e->pool != &consolepool) {
 		if ((errno = posix_spawn_file_actions_addopen(&actions, 0, "/dev/null", O_RDONLY, 0))) {
 			warn("posix_spawn_file_actions_addopen:");
@@ -541,24 +551,71 @@ queryload(void)
 #endif
 }
 
+/* returns remaining GNU/tokens */
+static void
+returngmake(void)
+{
+	if (buildopts.gmakepipe[1] >= 0) {
+		if (write(buildopts.gmakepipe[1], gmaketokens, gmakelatest - gmaketokens) < 0) {
+			warn("last write to jobserver:");
+		} else {
+			gmakelatest = gmaketokens;
+		}
+	}
+}
+
+static void
+termsignal(int signum)
+{
+	write(2, "samu: terminating due to signal\n", 32);
+	returngmake();
+	_exit(128 + signum);
+}
+
 void
 build(void)
 {
+	struct sigaction sact = { 0 };
 	struct job *jobs = NULL;
-	struct pollfd *fds = NULL;
+	struct pollfd *fds = NULL, tokenin = { .fd = -1, .events = POLLIN };
 	size_t i, next = 0, jobslen = 0, maxjobs = buildopts.maxjobs, numjobs = 0, numfail = 0;
+	ssize_t gmakeread;
 	struct edge *e;
 
 	if (ntotal == 0) {
 		warn("nothing to do");
 		return;
 	}
 
+	if (buildopts.gmakepipe[0] >= 0) {
+		if (atexit(returngmake) == 0) {
+			maxjobs = 1; /* will change dynamically as tokens are exchanged */
+			tokenin.fd = buildopts.gmakepipe[0];
+			sact.sa_handler = termsignal;
+			sigaction(SIGTERM, &sact, NULL);
+			sigaction(SIGINT, &sact, NULL);
+			sigaction(SIGPIPE, &sact, NULL);
+		} else {
+			warn("unable to register an atexit() function");
+		}
+	}
+
 	clock_gettime(CLOCK_MONOTONIC, &starttime);
 	formatstatus(NULL, 0);
 
 	nstarted = 0;
 	for (;;) {
+		/* see if GNU/make has authorized more jobs */
+		if (poll(&tokenin, 1, 0) > 0) {
+			gmakeread = gmakelatest - gmaketokens;
+			gmakeread = read(buildopts.gmakepipe[0], gmakelatest, 512 - (size_t)gmakeread > ntotal - nstarted ? ntotal - nstarted : 512 - gmakeread);
+			if (gmakeread < 0) {
+				warn("read from jobserver:");
+				gmakeread = 0;
+			}
+			gmakelatest += gmakeread;
+			maxjobs += gmakeread;
+		}
 		/* limit number of of jobs based on load */
 		if (buildopts.maxload)
 			maxjobs = queryload() > buildopts.maxload ? 1 : buildopts.maxjobs;
@@ -613,6 +670,13 @@ build(void)
 			next = i;
 			if (jobs[i].failed)
 				++numfail;
+			/* must return the GNU/tokens once a job is done */
+			if (buildopts.gmakepipe[1] > 0 && gmakelatest != gmaketokens) {
+				if (write(buildopts.gmakepipe[1], --gmakelatest, 1) < 0) {
+					warn("write to jobserver:");
+				}
+				--maxjobs;
+			}
 		}
 	}
 	for (i = 0; i < jobslen; ++i)

build.h

@@ -5,6 +5,7 @@ struct buildoptions {
 	_Bool verbose, explain, keepdepfile, keeprsp, dryrun;
 	const char *statusfmt;
 	double maxload;
+	int gmakepipe[2];
 };
 
 extern struct buildoptions buildopts;

samu.c

@@ -5,6 +5,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>  /* for chdir */
+#include <poll.h>   /* for poll  */
 #include "arg.h"
 #include "build.h"
 #include "deps.h"
@@ -90,6 +91,54 @@ jobsflag(const char *flag)
 	buildopts.maxjobs = num > 0 ? num : -1;
 }
 
+static void
+jobserverflags(const char *flag)
+{
+	int read_end, write_end;
+	struct pollfd check[2];
+
+	if (!flag)
+		return;
+	if (sscanf(flag, "%d,%d", &read_end, &write_end) == 2 && read_end >= 0 && write_end >= 0) {
+		/* assert valid fds */
+		check[0].fd = read_end;
+		check[1].fd = write_end;
+		if (poll(check, 2, 0) == -1 || check[0].revents & POLLNVAL || check[1].revents & POLLNVAL) {
+			fatal("jobserver fds are not open");
+			return;
+		}
+		buildopts.gmakepipe[0] = read_end;
+		buildopts.gmakepipe[1] = write_end;
+		warn("using GNU Make jobserver");
+	} else {
+		fatal("invalid jobserver parameter");
+	}
+}
+
+static void
+parsegmakeflags(char *env) {
+	char *arg;
+
+	if (!env)
+		return;
+	env = xmemdup(env, strlen(env) + 1);
+
+	arg = strtok(env, " ");
+	/* first word might contain dry run */
+	if (arg && strchr(arg, 'n'))
+		buildopts.dryrun = true;
+	arg = strtok(NULL, " ");
+	while (arg) {
+		if (strncmp(arg, "-j", 2) == 0) {
+			/* handled by parent process */
+		} else if (strncmp(arg, "--jobserver-auth=", 17) == 0 || strncmp(arg, "--jobserver-fds=", 16) == 0) {
+			jobserverflags(strchr(arg, '=')+1);
+		}
+		arg = strtok(NULL, " ");
+	}
+	free(env);
+}
+
 static void
 parseenvargs(char *env)
 {
@@ -149,6 +198,7 @@ main(int argc, char *argv[])
 
 	argv0 = progname(argv[0], "samu");
 	parseenvargs(getenv("SAMUFLAGS"));
+	parsegmakeflags(getenv("MAKEFLAGS"));
 	ARGBEGIN {
 	case '-':
 		arg = EARGF(usage());
@@ -201,7 +251,14 @@ main(int argc, char *argv[])
 		usage();
 	} ARGEND
 argdone:
-	if (!buildopts.maxjobs) {
+	if (buildopts.gmakepipe[0] >= 0) {
+		if (buildopts.maxjobs)
+			warn("ignoring -j setting as GNU Make job client is enabled");
+		if (buildopts.maxload)
+			warn("ignoring -l setting as GNU Make job client is enabled");
+		buildopts.maxjobs = -1;
+		buildopts.maxload = 0;
+	} else if (!buildopts.maxjobs) {
 #ifdef _SC_NPROCESSORS_ONLN
 		int n = sysconf(_SC_NPROCESSORS_ONLN);
 		switch (n) {