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Author SHA1 Message Date
jorijnvdgraaf
22fbef4ae1 Merge pull request 'fix: line-buffer stdout when redirected so progress/readiness lines flush (#18)' (#19) from claude/issue-18 into master
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Reviewed-on: #19
 2026-06-01 16:49:59 +02:00
catbot
0ff9050eb3 fix: line-buffer stdout when redirected so progress/readiness lines flush
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When crafter-build's stdout is not a TTY (redirected to a file or pipe) the
C runtime defaults to full (block) buffering. The progress path is TTY-aware
and the in-place redraw flushes explicitly, but the non-TTY append path
(`[N/M]` lines), Finalize()'s `Built N steps` line and the `-r` server's
`listening on port :N` line all go through block-buffered stdout with no
flush. They accumulate in the buffer and only spill at ~4KB boundaries.

On a normal build this is hidden because the C runtime flushes stdout at
exit. Under `-r` the process never exits — it blocks in its serve loop — so
the trailing buffer is never flushed: a redirected log freezes mid-build (or
sits at 0 bytes) even though the build finished and the server is already
answering. Any tooling that polls the log for `Built …` / `listening …` /
`[N/N]` hangs forever. This is the real cause of the frozen log misdiagnosed
as a build deadlock in #16.

Fix: switch stdout to line buffering at the very top of main(), before any
output, only when stdout is not a terminal. Every `\n` then flushes, so the
markers reach a redirected log immediately. No behaviour change on a TTY.

Kept self-contained in main.cpp using system headers (isatty + setvbuf)
rather than a new Crafter::Progress export: the self-hosting exe build
compiles main.cpp against the installed/cached Crafter.Build module BMIs,
which shadow the freshly built local ones, so a new interface symbol would
not be visible without reinstalling crafter-build first.

Resolves #18

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
 2026-06-01 14:42:33 +00:00
1 changed files with 24 additions and 0 deletions
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implementations/main.cpp
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@ -17,9 +17,33 @@ License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/ */
#include <cstdio>
#if defined(_WIN32)
#include <io.h>
#ifndef STDOUT_FILENO
#define STDOUT_FILENO _fileno(stdout)
#endif
#define CRAFTER_MAIN_ISATTY _isatty
#else
#include <unistd.h>
#define CRAFTER_MAIN_ISATTY isatty
#endif
import std; import std;
import Crafter.Build; import Crafter.Build;
int main(int argc, char** argv) { int main(int argc, char** argv) {
// Line-buffer stdout when it is not a terminal. Must run before any stdout
// write. When stdout is a regular file or pipe the C runtime defaults to
// full (block) buffering, so the append-only progress lines ("[N/M]") and
// the trailing "Built … steps" / "listening on port …" lines would sit in
// the buffer and never reach a redirected log — fatal for tooling that
// polls the log for a readiness marker, and worst under -r where the
// process blocks in its serve loop and never returns to flush. A TTY is
// already line-buffered and its in-place redraw path flushes explicitly, so
// only adjust when redirected.
if (CRAFTER_MAIN_ISATTY(STDOUT_FILENO) == 0) {
std::setvbuf(stdout, nullptr, _IOLBF, 0);
}
return Crafter::Run(argc, argv); return Crafter::Run(argc, argv);
} }