libutil: give Pid proper resource semantics

copy-constructing or assigning from pid_t can easily lead to duplicate
Pid instances for the same process if a pid_t was used carelessly, and
Pid itself was copy-constructible. both could cause surprising results
such as killing processes twice (which could become very problemantic,
but luckily modern systems don't reuse PIDs all that quickly), or more
than one piece of the code believing it owns a process when neither do

Change-Id: Ifea7445f84200b34c1a1d0acc2cdffe0f01e20c6

1 files changed, 4 insertions, 4 deletions

diff --git a/src/libstore/ssh.cc b/src/libstore/ssh.cc
index 0d7bfa01d..c40eba894 100644
--- a/src/libstore/ssh.cc
+++ b/src/libstore/ssh.cc
@@ -70,7 +70,7 @@ std::unique_ptr<SSHMaster::Connection> SSHMaster::startCommand(const std::string
     }
     Finally cleanup = [&]() { logger->resume(); };
 
-    conn->sshPid = startProcess([&]() {
+    conn->sshPid = Pid{startProcess([&]() {
         restoreProcessContext();
 
         close(in.writeSide.get());
@@ -99,7 +99,7 @@ std::unique_ptr<SSHMaster::Connection> SSHMaster::startCommand(const std::string
 
         // could not exec ssh/bash
         throw SysError("unable to execute '%s'", args.front());
-    }, options);
+    }, options)};
 
 
     in.readSide.reset();
@@ -147,7 +147,7 @@ Path SSHMaster::startMaster()
     if (isMasterRunning())
         return state->socketPath;
 
-    state->sshMaster = startProcess([&]() {
+    state->sshMaster = Pid{startProcess([&]() {
         restoreProcessContext();
 
         close(out.readSide.get());
@@ -160,7 +160,7 @@ Path SSHMaster::startMaster()
         execvp(args.begin()->c_str(), stringsToCharPtrs(args).data());
 
         throw SysError("unable to execute '%s'", args.front());
-    }, options);
+    }, options)};
 
     out.writeSide.reset();