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 #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);
  }
 }