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nghttpx: Write PID in temporary file then rename 

Write PID in temporary file first.  Then rename it as the real
destination.  It will avoid the issue that the external process may
read the empty PID file because of race condition.
This commit is contained in:
Tatsuhiro Tsujikawa 2016-05-23 22:39:38 +09:00
parent 65135bc319
commit c308be39de
1 changed files with 47 additions and 7 deletions
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54
src/shrpx.cc
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@ -200,18 +200,58 @@ int chown_to_running_user(const char *path) {
namespace { namespace {
void save_pid() { void save_pid() {
std::ofstream out(get_config()->pid_file.c_str(), std::ios::binary); constexpr auto SUFFIX = StringRef::from_lit(".XXXXXX");
out << get_config()->pid << "\n"; auto &pid_file = get_config()->pid_file;
out.close();
if (!out) { std::vector<char> temp_path;
LOG(ERROR) << "Could not save PID to file " << get_config()->pid_file; temp_path.reserve(get_config()->pid_file.size() + SUFFIX.size() + 1);
auto p = std::copy(std::begin(pid_file), std::end(pid_file),
std::begin(temp_path));
p = std::copy(std::begin(SUFFIX), std::end(SUFFIX), p);
*p = '\0';
auto fd = mkstemp(temp_path.data());
if (fd == -1) {
auto error = errno;
LOG(ERROR) << "Could not save PID to file " << pid_file << ": "
<< strerror(error);
exit(EXIT_FAILURE);
}
auto content = util::utos(get_config()->pid) + '\n';
if (write(fd, content.c_str(), content.size()) == -1) {
auto error = errno;
LOG(ERROR) << "Could not save PID to file " << pid_file << ": "
<< strerror(error);
exit(EXIT_FAILURE);
}
if (fsync(fd) == -1) {
auto error = errno;
LOG(ERROR) << "Could not save PID to file " << pid_file << ": "
<< strerror(error);
exit(EXIT_FAILURE);
}
close(fd);
if (rename(temp_path.data(), pid_file.c_str()) == -1) {
auto error = errno;
LOG(ERROR) << "Could not save PID to file " << pid_file << ": "
<< strerror(error);
unlink(temp_path.data());
exit(EXIT_FAILURE); exit(EXIT_FAILURE);
} }
if (get_config()->uid != 0) { if (get_config()->uid != 0) {
if (chown_to_running_user(get_config()->pid_file.c_str()) == -1) { if (chown_to_running_user(pid_file.c_str()) == -1) {
auto error = errno; auto error = errno;
LOG(WARN) << "Changing owner of pid file " << get_config()->pid_file LOG(WARN) << "Changing owner of pid file " << pid_file
<< " failed: " << strerror(error); << " failed: " << strerror(error);
} }
} }