Make iprof a transparent stdio wrapper

integration_tests/buffering_helper.c

@@ -0,0 +1,20 @@
+/*
+ * Helper for the iprof stdout/stderr streaming tests.
+ *
+ * It uses plain stdio (printf/fprintf) with NO explicit fflush, so the C
+ * library decides the buffering policy from whether the fd is a tty:
+ *   - tty       -> line-buffered  -> each line is emitted as it is printed
+ *   - pipe/file -> block-buffered -> everything is flushed only at exit
+ */
+#include <stdio.h>
+#include <unistd.h>
+
+#define SLEEP_SECONDS 4
+
+int main(void) {
+  printf("THAPI_STREAM_FIRST\n");
+  fprintf(stderr, "THAPI_STREAM_STDERR\n");
+  sleep(SLEEP_SECONDS);
+  printf("THAPI_STREAM_SECOND\n");
+  return 0;
+}

integration_tests/parallel_execution.bats

@@ -59,24 +59,38 @@ launch_mpi() {
 }
 
 @test "launch_usr_bin_streams_child_stdout" {
-  # Verify iprof streams the user binary's stdout line-by-line rather than
-  # buffering it. The child sleeps 4s between two prints, so under proper
-  # streaming the two lines reach us ~4s apart; under buffering they arrive
-  # together at child exit. We assert the gap is at least 2s.
+  # If iprof's input is not buffered, iprof should not buffer it. We use `script`
+  # to give iprof a tty (an unbuffered pipe); the helper sleeps 4s between two
+  # prints, so under streaming the two lines reach us ~4s apart. `script` runs the
+  # child under a PTY, whose line discipline appends a CR to each '\n', hence the
+  # trailing `*` in the patterns below.
+  helper="${BATS_TEST_TMPDIR}/buffering_helper"
+  gcc "${BATS_TEST_DIRNAME}/buffering_helper.c" -o "${helper}"
+
   ts_first=""
   ts_second=""
   while IFS= read -r line; do
     case "$line" in
-      THAPI_STREAM_FIRST) ts_first=$(date +%s%N) ;;
-      THAPI_STREAM_SECOND)
+      THAPI_STREAM_FIRST*) ts_first=$(date +%s%N) ;;
+      THAPI_STREAM_SECOND*)
         ts_second=$(date +%s%N)
         break
         ;;
     esac
-  done < <(iprof -- bash -c 'echo THAPI_STREAM_FIRST; sleep 4; echo THAPI_STREAM_SECOND' 2>/dev/null)
+  done < <(script -qec "iprof -- '${helper}'" /dev/null)
   [ -n "$ts_first" ]
   [ -n "$ts_second" ]
   delta_ms=$(((ts_second - ts_first) / 1000000))
   echo "delta_ms=$delta_ms"
   [ "$delta_ms" -gt 2000 ]
 }
+
+@test "launch_usr_bin_keeps_stderr_separate" {
+  # The user binary's stdout and stderr must stay on their respective streams.
+  helper="${BATS_TEST_TMPDIR}/buffering_helper"
+  gcc "${BATS_TEST_DIRNAME}/buffering_helper.c" -o "${helper}"
+
+  run --separate-stderr iprof --no-analysis -- "${helper}"
+  [[ "$output" =~ $'THAPI_STREAM_FIRST\nTHAPI_STREAM_SECOND' ]]
+  [[ "$stderr" =~ THAPI_STREAM_STDERR ]]
+}

xprof/xprof.rb.in

@@ -26,7 +26,6 @@ require 'open3'
 require 'fileutils'
 require 'etc'
 require 'optparse_thapi'
-require 'pty'
 require 'digest/md5'
 require 'socket'
 require 'io/nonblock'
@@ -98,17 +97,18 @@ end
 def launch_usr_bin(env, cmd)
   LOGGER.info { "Launch_usr_bin #{cmd}" }
 
-  # https://docs.ruby-lang.org/en/master/IO.html#method-i-sync
-  $stdout.sync = true
-  IO.popen(env, cmd) do |io|
-    io.each { |line| print line }
+  # Let the user binary inherit our own stdout/stderr directly. Iprof is a
+  # transparent wrapper.
+  begin
+    pid = spawn(env, *cmd, out: $stdout, err: $stderr)
+    _, status = Process.wait2(pid)
   rescue Interrupt
     # Just continue as usual, do not crash xprof
   rescue Errno::ENOENT
     warn("#{__FILE__}: Can't find executable #{cmd.first}")
     raise Errno::ENOENT
   end
-  XprofExitCode.update($?, cmd.join(' '))
+  XprofExitCode.update(status, cmd.join(' ')) if status
 end
 
 def exec_store_in_file(cmd, output_file: nil)