1 files changed, 117 insertions, 18 deletions

diff --git a/findutils/xargs.c b/findutils/xargs.c
index b4e3db02c..77e01ef6c 100644
--- a/findutils/xargs.c
+++ b/findutils/xargs.c
@@ -59,6 +59,11 @@
 //config:       depends on XARGS
 //config:       help
 //config:       Support -I STR and -i[STR] options.
+//config:
+//config:config FEATURE_XARGS_SUPPORT_PARALLEL
+//config:       bool "Enable -P N: processes to run in parallel"
+//config:       default y
+//config:       depends on XARGS
 
 //applet:IF_XARGS(APPLET_NOEXEC(xargs, xargs, BB_DIR_USR_BIN, BB_SUID_DROP, xargs))
 
@@ -99,38 +104,121 @@ struct globals {
 #endif
         const char *eof_str;
         int idx;
+#if ENABLE_FEATURE_XARGS_SUPPORT_PARALLEL
+        int running_procs;
+        int max_procs;
+#endif
+        smalluint xargs_exitcode;
 } FIX_ALIASING;
 #define G (*(struct globals*)bb_common_bufsiz1)
 #define INIT_G() do { \
         setup_common_bufsiz(); \
         G.eof_str = NULL; /* need to clear by hand because we are NOEXEC applet */ \
         G.idx = 0; \
+        IF_FEATURE_XARGS_SUPPORT_PARALLEL(G.running_procs = 0;) \
+        IF_FEATURE_XARGS_SUPPORT_PARALLEL(G.max_procs = 1;) \
+        G.xargs_exitcode = 0; \
         IF_FEATURE_XARGS_SUPPORT_REPL_STR(G.repl_str = "{}";) \
         IF_FEATURE_XARGS_SUPPORT_REPL_STR(G.eol_ch = '\n';) \
 } while (0)
 
 
+/*
+ * Returns 0 if xargs should continue (but may set G.xargs_exitcode to 123).
+ * Else sets G.xargs_exitcode to error code and returns nonzero.
+ *
+ * If G.max_procs == 0, performs final waitpid() loop for all children.
+ */
 static int xargs_exec(void)
 {
         int status;
 
+#if !ENABLE_FEATURE_XARGS_SUPPORT_PARALLEL
         status = spawn_and_wait(G.args);
+#else
+        if (G.max_procs == 1) {
+                status = spawn_and_wait(G.args);
+        } else {
+                pid_t pid;
+                int wstat;
+ again:
+                if (G.running_procs >= G.max_procs)
+                        pid = safe_waitpid(-1, &wstat, 0);
+                else
+                        pid = wait_any_nohang(&wstat);
+                if (pid > 0) {
+                        /* We may have children we don't know about:
+                         * sh -c 'sleep 1 & exec xargs ...'
+                         * Do not make G.running_procs go negative.
+                         */
+                        if (G.running_procs != 0)
+                                G.running_procs--;
+                        status = WIFSIGNALED(wstat)
+                                ? 0x180 + WTERMSIG(wstat)
+                                : WEXITSTATUS(wstat);
+                        if (status > 0 && status < 255) {
+                                /* See below why 123 does not abort */
+                                G.xargs_exitcode = 123;
+                                status = 0;
+                        }
+                        if (status == 0)
+                                goto again; /* maybe we have more children? */
+                        /* else: "bad" status, will bail out */
+                } else if (G.max_procs != 0) {
+                        /* Not in final waitpid() loop,
+                         * and G.running_procs < G.max_procs: start more procs
+                         */
+                        status = spawn(G.args);
+                        /* here "status" actually holds pid, or -1 */
+                        if (status > 0) {
+                                G.running_procs++;
+                                status = 0;
+                        }
+                        /* else: status == -1 (failed to fork or exec) */
+                } else {
+                        /* final waitpid() loop: must be ECHILD "no more children" */
+                        status = 0;
+                }
+        }
+#endif
+        /* Manpage:
+         * """xargs exits with the following status:
+         * 0 if it succeeds
+         * 123 if any invocation of the command exited with status 1-125
+         * 124 if the command exited with status 255
+         *     ("""If any invocation of the command exits with a status of 255,
+         *     xargs will stop immediately without reading any further input.
+         *     An error message is issued on stderr when this happens.""")
+         * 125 if the command is killed by a signal
+         * 126 if the command cannot be run
+         * 127 if the command is not found
+         * 1 if some other error occurred."""
+         */
         if (status < 0) {
                 bb_simple_perror_msg(G.args[0]);
-                return errno == ENOENT ? 127 : 126;
-        }
-        if (status == 255) {
-                bb_error_msg("%s: exited with status 255; aborting", G.args[0]);
-                return 124;
+                status = (errno == ENOENT) ? 127 : 126;
         }
-        if (status >= 0x180) {
+        else if (status >= 0x180) {
                 bb_error_msg("'%s' terminated by signal %d",
                         G.args[0], status - 0x180);
-                return 125;
+                status = 125;
         }
-        if (status)
-                return 123;
-        return 0;
+        else if (status != 0) {
+                if (status == 255) {
+                        bb_error_msg("%s: exited with status 255; aborting", G.args[0]);
+                        return 124;
+                }
+                /* "123 if any invocation of the command exited with status 1-125"
+                 * This implies that nonzero exit code is remembered,
+                 * but does not cause xargs to stop: we return 0.
+                 */
+                G.xargs_exitcode = 123;
+                status = 0;
+        }
+
+        if (status != 0)
+                G.xargs_exitcode = status;
+        return status;
 }
 
 /* In POSIX/C locale isspace is only these chars: "\t\n\v\f\r" and space.
@@ -436,6 +524,9 @@ static int xargs_ask_confirmation(void)
 //usage:        IF_FEATURE_XARGS_SUPPORT_REPL_STR(
 //usage:     "\n        -I STR  Replace STR within PROG ARGS with input line"
 //usage:        )
+//usage:        IF_FEATURE_XARGS_SUPPORT_PARALLEL(
+//usage:     "\n        -P N    Run up to N PROGs in parallel"
+//usage:        )
 //usage:        IF_FEATURE_XARGS_SUPPORT_TERMOPT(
 //usage:     "\n        -x      Exit if size is exceeded"
 //usage:        )
@@ -473,14 +564,14 @@ enum {
         IF_FEATURE_XARGS_SUPPORT_CONFIRMATION("p") \
         IF_FEATURE_XARGS_SUPPORT_TERMOPT(     "x") \
         IF_FEATURE_XARGS_SUPPORT_ZERO_TERM(   "0") \
-        IF_FEATURE_XARGS_SUPPORT_REPL_STR(    "I:i::")
+        IF_FEATURE_XARGS_SUPPORT_REPL_STR(    "I:i::") \
+        IF_FEATURE_XARGS_SUPPORT_PARALLEL(    "P:+")
 
 int xargs_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int xargs_main(int argc UNUSED_PARAM, char **argv)
 {
         int initial_idx;
         int i;
-        int child_error = 0;
         char *max_args;
         char *max_chars;
         char *buf;
@@ -500,8 +591,14 @@ int xargs_main(int argc UNUSED_PARAM, char **argv)
                 "no-run-if-empty\0" No_argument "r",
                 &max_args, &max_chars, &G.eof_str, &G.eof_str
                 IF_FEATURE_XARGS_SUPPORT_REPL_STR(, &G.repl_str, &G.repl_str)
+                IF_FEATURE_XARGS_SUPPORT_PARALLEL(, &G.max_procs)
         );
 
+#if ENABLE_FEATURE_XARGS_SUPPORT_PARALLEL
+        if (G.max_procs <= 0) /* -P0 means "run lots of them" */
+                G.max_procs = 100; /* let's not go crazy high */
+#endif
+
         /* -E ""? You may wonder why not just omit -E?
          * This is used for portability:
          * old xargs was using "_" as default for -E / -e */
@@ -620,11 +717,8 @@ int xargs_main(int argc UNUSED_PARAM, char **argv)
                 }
 
                 if (!(opt & OPT_INTERACTIVE) || xargs_ask_confirmation()) {
-                        child_error = xargs_exec();
-                }
-
-                if (child_error > 0 && child_error != 123) {
-                        break;
+                        if (xargs_exec() != 0)
+                                break; /* G.xargs_exitcode is set by xargs_exec() */
                 }
 
                 overlapping_strcpy(buf, rem);
@@ -635,7 +729,12 @@ int xargs_main(int argc UNUSED_PARAM, char **argv)
                 free(buf);
         }
 
-        return child_error;
+#if ENABLE_FEATURE_XARGS_SUPPORT_PARALLEL
+        G.max_procs = 0;
+        xargs_exec(); /* final waitpid() loop */
+#endif
+
+        return G.xargs_exitcode;
 }