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#include <assert.h>
#include <cstring>
#include <iostream>
#include <mutex>
#include <string.h>
#include <sys/wait.h>
#include <thread>
#include <unistd.h>
#include <vector>
pid_t g_pid = 0;
std::mutex g_child_pids_mutex;
std::vector<pid_t> g_child_pids;
const char *g_program = nullptr;
bool g_use_vfork = true; // Use vfork by default.
bool g_call_exec = false; // Does not call exec by default.
int call_vfork(int index) {
pid_t child_pid = 0;
if (g_use_vfork) {
child_pid = vfork();
} else {
child_pid = fork();
}
if (child_pid == -1) {
// Error handling
perror("vfork");
return 1;
} else if (child_pid == 0) {
// This code is executed by the child process
g_pid = getpid();
printf("Child process: %d\n", g_pid);
if (g_call_exec) {
std::string child_exit_code = std::to_string(index + 10);
execl(g_program, g_program, "--child", child_exit_code.c_str(), NULL);
} else {
_exit(index + 10);
}
} else {
// This code is executed by the parent process
printf("[Parent] Forked process id: %d\n", child_pid);
}
return 0;
}
void wait_all_children_to_exit() {
std::lock_guard<std::mutex> Lock(g_child_pids_mutex);
for (pid_t child_pid : g_child_pids) {
int child_status = 0;
pid_t pid = waitpid(child_pid, &child_status, 0);
if (child_status != 0) {
int exit_code = WEXITSTATUS(child_status);
if (exit_code > 15 || exit_code < 10) {
printf("Error: child process exits with unexpected code %d\n",
exit_code);
_exit(1); // This will let our program know that some child processes
// didn't exist with an expected exit status.
}
}
if (pid != child_pid)
_exit(2); // This will let our program know it didn't succeed
}
}
void create_threads(int num_threads) {
std::vector<std::thread> threads;
for (int i = 0; i < num_threads; ++i) {
threads.emplace_back(std::thread(call_vfork, i));
}
printf("Created %d threads, joining...\n",
num_threads); // end_of_create_threads
for (auto &thread : threads) {
thread.join();
}
wait_all_children_to_exit();
}
// Can be called in various ways:
// 1. [program]: use vfork and not call exec
// 2. [program] --fork: use fork and not call exec
// 3. [program] --fork --exec: use fork and call exec
// 4. [program] --exec: use vfork and call exec
// 5. [program] --child [exit_code]: child process
int main(int argc, char *argv[]) {
g_pid = getpid();
g_program = argv[0];
for (int i = 1; i < argc; ++i) {
if (strcmp(argv[i], "--child") == 0) {
assert(i + 1 < argc);
int child_exit_code = std::stoi(argv[i + 1]);
printf("Child process: %d, exiting with code %d\n", g_pid,
child_exit_code);
_exit(child_exit_code);
} else if (strcmp(argv[i], "--fork") == 0)
g_use_vfork = false;
else if (strcmp(argv[i], "--exec") == 0)
g_call_exec = true;
}
int num_threads = 5; // break here
create_threads(num_threads);
return 0;
}
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