std: Add an unstable method Child::id

This commits adds a method to the `std::process` module to get the process
identifier of the child as a `u32`. On Windows the underlying identifier is
already a `u32`, and on Unix the type is typically defined as `c_int` (`i32` for
almost all our supported platforms), but the actually pid is normally a small
positive number.

Eventually we may add functions to load information about a process based on its
identifier or the ability to terminate a process based on its identifier, but
for now this function should enable this sort of functionality to exist outside
the standard library.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/libstd/process.rs b/src/libstd/process.rs
index 61398e16ba0..ae9316ddd62 100644
--- a/src/libstd/process.rs
+++ b/src/libstd/process.rs
@@ -456,6 +456,12 @@ impl Child {
         unsafe { self.handle.kill() }
     }
 
+    /// Returns the OS-assigned process identifier associated with this child.
+    #[unstable(feature = "process_id", reason = "api recently added")]
+    pub fn id(&self) -> u32 {
+        self.handle.id()
+    }
+
     /// Waits for the child to exit completely, returning the status that it
     /// exited with. This function will continue to have the same return value
     /// after it has been called at least once.