process-wrapper: Wait for all (grand)children before exiting.

This uses Linux's PR_SET_CHILD_SUBREAPER and FreeBSD's PROC_REAP_ACQUIRE features to become an init-like process for all (grand)children spawned by process-wrapper, which allows us to a) kill them reliably and then b) wait for them reliably. Before this change, we only killed the main child, waited for it, then fired off a kill -9 on the process group, without waiting for it. This led to a race condition where Bazel would try to use or delete files that were still helt open by children of the main child and thus to bugs like bazelbuild#2371.

This means we now have reliable process management on Linux, FreeBSD and Windows. Unfortunately I couldn't find any feature like this on macOS, so this is the only OS that will still have this race condition.

PiperOrigin-RevId: 153817210

src/main/tools/BUILD

@@ -1,20 +1,28 @@
 package(default_visibility = ["//src:__subpackages__"])
 
+cc_library(
+    name = "process-tools",
+    srcs = [
+        "process-tools.cc",
+        "process-tools.h",
+    ],
+)
+
 cc_binary(
     name = "process-wrapper",
     srcs = select({
         "//src:windows_msvc": ["process-wrapper-windows.cc"],
         "//conditions:default": [
-            "process-tools.c",
-            "process-tools.h",
-            "process-wrapper.c",
+            "process-wrapper.cc",
         ],
     }),
-    copts = select({
+    linkopts = ["-lm"],
+    deps = select({
         "//src:windows_msvc": [],
-        "//conditions:default": ["-std=c99"],
+        "//conditions:default": [
+            ":process-tools",
+        ],
     }),
-    linkopts = ["-lm"],
 )
 
 cc_binary(
@@ -45,6 +53,17 @@ cc_binary(
         ],
     }),
     linkopts = ["-lm"],
+    deps = select({
+        "//src:darwin": [],
+        "//src:darwin_x86_64": [],
+        "//src:freebsd": [],
+        "//src:windows": [],
+        "//src:windows_msys": [],
+        "//src:windows_msvc": [],
+        "//conditions:default": [
+            ":process-tools",
+        ],
+    }),
 )
 
 filegroup(

src/main/tools/linux-sandbox-options.cc

@@ -12,14 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#include "linux-sandbox-options.h"
-#include "linux-sandbox-utils.h"
+#include "src/main/tools/linux-sandbox-options.h"
 
 #define DIE(args...)                                     \
   {                                                      \
     fprintf(stderr, __FILE__ ":" S__LINE__ ": \"" args); \
     fprintf(stderr, "\": ");                             \
-    perror(NULL);                                        \
+    perror(nullptr);                                     \
     exit(EXIT_FAILURE);                                  \
   }
 
@@ -39,6 +38,8 @@
 #include <string>
 #include <vector>
 
+#include "src/main/tools/linux-sandbox-utils.h"
+
 using std::ifstream;
 using std::unique_ptr;
 using std::vector;
@@ -199,6 +200,7 @@ static void ParseCommandLine(unique_ptr<vector<char *>> args) {
   if (optind < static_cast<int>(args->size())) {
     if (opt.args.empty()) {
       opt.args.assign(args->begin() + optind, args->end());
+      opt.args.push_back(nullptr);
     } else {
       Usage(args->front(), "Merging commands not supported.");
     }
@@ -207,8 +209,8 @@ static void ParseCommandLine(unique_ptr<vector<char *>> args) {
 
 // Expands a single argument, expanding options @filename to read in the content
 // of the file and add it to the list of processed arguments.
-unique_ptr<vector<char *>> ExpandArgument(unique_ptr<vector<char *>> expanded,
-                                          char *arg) {
+static unique_ptr<vector<char *>> ExpandArgument(
+    unique_ptr<vector<char *>> expanded, char *arg) {
   if (arg[0] == '@') {
     const char *filename = arg + 1;  // strip off the '@'.
     ifstream f(filename);
@@ -236,7 +238,7 @@ unique_ptr<vector<char *>> ExpandArgument(unique_ptr<vector<char *>> expanded,
 // Pre-processes an argument list, expanding options @filename to read in the
 // content of the file and add it to the list of arguments. Stops expanding
 // arguments once it encounters "--".
-unique_ptr<vector<char *>> ExpandArguments(const vector<char *> &args) {
+static unique_ptr<vector<char *>> ExpandArguments(const vector<char *> &args) {
   unique_ptr<vector<char *>> expanded(new vector<char *>());
   expanded->reserve(args.size());
   for (auto arg = args.begin(); arg != args.end(); ++arg) {
@@ -260,6 +262,6 @@ void ParseOptions(int argc, char *argv[]) {
   }
 
   if (opt.working_dir.empty()) {
-    opt.working_dir = getcwd(NULL, 0);
+    opt.working_dir = getcwd(nullptr, 0);
   }
 }