parallel: Implement -l (maxload) and -i (replace {})

Add support for only starting jobs when the load average is low
enough, this is done with -l and acts similarly to how make does it.

In order to construct more complex commands, add -i which will make
parallel replace {} with the argument at an arbitrary place in the
command line.

diff --git a/parallel.c b/parallel.c
index 2333a3dc3a860613d7a01958a11cd7ae3a02de31..438bc935020b7e739c6a6dfcf98aab786e394a08 100644 (file)
--- a/parallel.c
+++ b/parallel.c
@@ -38,7 +38,7 @@ void usage()
        exit(1);
 }
 
-void exec_child(char **command, char *argument)
+void exec_child(char **command, char *argument, int replace_cb)
 {
        char **argv;
        int argc = 0;
@@ -47,12 +47,16 @@ void exec_child(char **command, char *argument)
        while (command[argc] != 0) {
                argc++;
        }
-       argc++;
+       if (replace_cb == 0)
+               argc++;
        argv = calloc(sizeof(char*), argc+1);
        for (i = 0; i < argc; i++) {
                argv[i] = command[i];
+               if (replace_cb && (strcmp(argv[i], "{}") == 0))
+                       argv[i] = argument;
        }
-       argv[i-1] = argument;
+       if (replace_cb == 0)
+               argv[i-1] = argument;
        if (fork() == 0) {
                /* Child */
                execvp(argv[0], argv);
@@ -61,11 +65,15 @@ void exec_child(char **command, char *argument)
        return;
 }
 
-int wait_for_child(void)
+int wait_for_child(int options)
 {
        id_t id_ignored = 0;
        siginfo_t infop;
-       waitid(P_ALL, id_ignored, &infop, WEXITED);
+
+       infop.si_pid = 0;
+       waitid(P_ALL, id_ignored, &infop, WEXITED | options);
+       if (infop.si_pid == 0)
+               return -1; /* Nothing to wait for */
        if (infop.si_code == CLD_EXITED)
                return infop.si_status;
        return 1;
@@ -82,12 +90,16 @@ int main(int argc, char **argv)
        int argidx = 0;
        int cidx = 0;
        int returncode = 0;
+       int replace_cb = 0;
 
-       while ((opt = getopt(argc, argv, "+hj:l:")) != -1) {
+       while ((opt = getopt(argc, argv, "+hij:l:")) != -1) {
                switch (opt) {
                case 'h':
                        usage();
                        break;
+               case 'i':
+                       replace_cb = 1;
+                       break;
                case 'j':
                        maxjobs = atoi(optarg);
                        break;
@@ -100,7 +112,7 @@ int main(int argc, char **argv)
                }
        }
 
-       if (maxjobs < 0) {
+       if (maxjobs < 0 && maxload < 0) {
                usage();
        }
 
@@ -130,19 +142,35 @@ int main(int argc, char **argv)
        }
 
        while (arguments[argidx] != 0) {
-               if (maxjobs > 0 && curjobs < maxjobs) {
-                       exec_child(command, arguments[argidx]);
+               double load;
+
+               getloadavg(&load, 1);
+
+               if ((maxjobs > 0 && curjobs < maxjobs) ||
+                   (maxload > 0 && load < maxload)) {
+                       exec_child(command, arguments[argidx], replace_cb);
                        argidx++;
                        curjobs++;
                }
 
                if (maxjobs > 0 && curjobs == maxjobs) {
-                       returncode |= wait_for_child();
+                       returncode |= wait_for_child(0);
                        curjobs--;
                }
+
+               if (maxload > 0 && load > maxload) {
+                       int r;
+                       sleep(1); /* XXX We should have a better
+                                  * heurestic than this */
+                       r = wait_for_child(WNOHANG);
+                       if (r > 0) {
+                               returncode |= r;
+                               curjobs--;
+                       }
+               }
        }
        while (curjobs > 0) {
-               returncode |= wait_for_child();
+               returncode |= wait_for_child(0);
                curjobs--;
        }