feat(unstable): Deno.ppid (#6539)

6 files changed, 91 insertions, 2 deletions

diff --git a/cli/Cargo.toml b/cli/Cargo.toml
index 11665023d..64688d5d0 100644
--- a/cli/Cargo.toml
+++ b/cli/Cargo.toml
@@ -64,7 +64,7 @@ swc_ecma_visit = "0.7.0"
 
 [target.'cfg(windows)'.dependencies]
 winapi = { version = "0.3.8", features = ["knownfolders", "objbase", "shlobj",
-"winbase", "winerror"] }
+"winbase", "winerror", "tlhelp32"] }
 fwdansi = "1.1.0"
 
 [target.'cfg(unix)'.dependencies]
diff --git a/cli/js/lib.deno.unstable.d.ts b/cli/js/lib.deno.unstable.d.ts
index 20096cb28..cec4f7f46 100644
--- a/cli/js/lib.deno.unstable.d.ts
+++ b/cli/js/lib.deno.unstable.d.ts
@@ -1194,4 +1194,9 @@ declare namespace Deno {
    * ```
    */
   export function fstat(rid: number): Promise<FileInfo>;
+
+  /** **UNSTABLE**: New API, yet to be vetted.
+   * The pid of the current process's parent.
+   */
+  export const ppid: number;
 }
diff --git a/cli/js/ops/runtime.ts b/cli/js/ops/runtime.ts
index 70addf469..09208df6d 100644
--- a/cli/js/ops/runtime.ts
+++ b/cli/js/ops/runtime.ts
@@ -9,6 +9,7 @@ export interface Start {
   denoVersion: string;
   noColor: boolean;
   pid: number;
+  ppid: number;
   repl: boolean;
   target: string;
   tsVersion: string;
diff --git a/cli/js/runtime_main.ts b/cli/js/runtime_main.ts
index 25a6b0f93..0c579626b 100644
--- a/cli/js/runtime_main.ts
+++ b/cli/js/runtime_main.ts
@@ -96,10 +96,11 @@ export function bootstrapMainRuntime(): void {
     }
   });
 
-  const { args, cwd, noColor, pid, repl, unstableFlag } = runtime.start();
+  const { args, cwd, noColor, pid, ppid, repl, unstableFlag } = runtime.start();
 
   Object.defineProperties(denoNs, {
     pid: readOnly(pid),
+    ppid: readOnly(ppid),
     noColor: readOnly(noColor),
     args: readOnly(Object.freeze(args)),
   });
diff --git a/cli/ops/runtime.rs b/cli/ops/runtime.rs
index e47b40792..1e426ad8a 100644
--- a/cli/ops/runtime.rs
+++ b/cli/ops/runtime.rs
@@ -32,6 +32,7 @@ fn op_start(
     "denoVersion": version::DENO,
     "noColor": !colors::use_color(),
     "pid": std::process::id(),
+    "ppid": ppid(),
     "repl": gs.flags.subcommand == DenoSubcommand::Repl,
     "target": env!("TARGET"),
     "tsVersion": version::TYPESCRIPT,
@@ -78,3 +79,62 @@ fn op_metrics(
     "bytesReceived": m.bytes_received
   })))
 }
+
+fn ppid() -> Value {
+  #[cfg(windows)]
+  {
+    // Adopted from rustup:
+    // https://github.com/rust-lang/rustup/blob/1.21.1/src/cli/self_update.rs#L1036
+    // Copyright Diggory Blake, the Mozilla Corporation, and rustup contributors.
+    // Licensed under either of
+    // - Apache License, Version 2.0
+    // - MIT license
+    use std::mem;
+    use winapi::shared::minwindef::DWORD;
+    use winapi::um::handleapi::{CloseHandle, INVALID_HANDLE_VALUE};
+    use winapi::um::processthreadsapi::GetCurrentProcessId;
+    use winapi::um::tlhelp32::{
+      CreateToolhelp32Snapshot, Process32First, Process32Next, PROCESSENTRY32,
+      TH32CS_SNAPPROCESS,
+    };
+    unsafe {
+      // Take a snapshot of system processes, one of which is ours
+      // and contains our parent's pid
+      let snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
+      if snapshot == INVALID_HANDLE_VALUE {
+        return serde_json::to_value(-1).unwrap();
+      }
+
+      let mut entry: PROCESSENTRY32 = mem::zeroed();
+      entry.dwSize = mem::size_of::<PROCESSENTRY32>() as DWORD;
+
+      // Iterate over system processes looking for ours
+      let success = Process32First(snapshot, &mut entry);
+      if success == 0 {
+        CloseHandle(snapshot);
+        return serde_json::to_value(-1).unwrap();
+      }
+
+      let this_pid = GetCurrentProcessId();
+      while entry.th32ProcessID != this_pid {
+        let success = Process32Next(snapshot, &mut entry);
+        if success == 0 {
+          CloseHandle(snapshot);
+          return serde_json::to_value(-1).unwrap();
+        }
+      }
+      CloseHandle(snapshot);
+
+      // FIXME: Using the process ID exposes a race condition
+      // wherein the parent process already exited and the OS
+      // reassigned its ID.
+      let parent_id = entry.th32ParentProcessID;
+      serde_json::to_value(parent_id).unwrap()
+    }
+  }
+  #[cfg(not(windows))]
+  {
+    use std::os::unix::process::parent_id;
+    serde_json::to_value(parent_id()).unwrap()
+  }
+}
diff --git a/cli/tests/unit/os_test.ts b/cli/tests/unit/os_test.ts
index b737d939a..e969464e5 100644
--- a/cli/tests/unit/os_test.ts
+++ b/cli/tests/unit/os_test.ts
@@ -111,6 +111,28 @@ unitTest(function osPid(): void {
   assert(Deno.pid > 0);
 });
 
+unitTest(function osPpid(): void {
+  assert(Deno.ppid > 0);
+});
+
+unitTest(
+  { perms: { run: true, read: true } },
+  async function osPpidIsEqualToPidOfParentProcess(): Promise<void> {
+    const decoder = new TextDecoder();
+    const process = Deno.run({
+      cmd: [Deno.execPath(), "eval", "-p", "--unstable", "Deno.ppid"],
+      stdout: "piped",
+      env: { NO_COLOR: "true" },
+    });
+    const output = await process.output();
+    process.close();
+
+    const expected = Deno.pid;
+    const actual = parseInt(decoder.decode(output));
+    assertEquals(actual, expected);
+  }
+);
+
 unitTest({ perms: { read: true } }, function execPath(): void {
   assertNotEquals(Deno.execPath(), "");
 });