[pacman-dev] [PATCH v2] cache terminal column width and handle SIGWINCH

[Simon Gomizelj]

Instead of doing ioctl each time, cache the result. Handle SIGWINCH to
we know the size of the terminal has changed (clear the cache).
---
Inspired by systemd. This is to set things up for paging, as paging
would require caching this value. Once the pager is up, there's no way
to poll for columns.

 src/pacman/pacman.c | 10 ++++++++++
 src/pacman/util.c   | 23 ++++++++++++++++++-----
 src/pacman/util.h   |  1 +
 3 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/src/pacman/pacman.c b/src/pacman/pacman.c
index df73bcf..1643a63 100644
--- a/src/pacman/pacman.c
+++ b/src/pacman/pacman.c
@@ -1044,6 +1044,16 @@ int main(int argc, char *argv[])
 		}
 	}
 
+	new_action.sa_handler = columns_reset;
+	sigemptyset(&new_action.sa_mask);
+	new_action.sa_flags = 0;
+
+	sigaction(SIGWINCH, NULL, &old_action);
+	if(old_action.sa_handler != SIG_IGN) {
+		sigaction(SIGWINCH, &new_action, NULL);
+	}
+
+
 	/* i18n init */
 #if defined(ENABLE_NLS)
 	localize();
diff --git a/src/pacman/util.c b/src/pacman/util.c
index 23eea98..1dd3235 100644
--- a/src/pacman/util.c
+++ b/src/pacman/util.c
@@ -46,6 +46,7 @@
 #include "conf.h"
 #include "callback.h"
 
+static volatile unsigned cached_columns = 0;
 
 struct table_cell_t {
 	char *label;
@@ -155,29 +156,41 @@ static int flush_term_input(int fd)
 	return 0;
 }
 
+/* intended to be used as a SIGWINCH handler */
+void columns_reset(int signum)
+{
+	cached_columns = 0;
+}
+
 /* gets the current screen column width */
 unsigned short getcols(int fd)
 {
 	const unsigned short default_tty = 80;
 	const unsigned short default_notty = 0;
-	unsigned short termwidth = 0;
+	unsigned short columns = 0;
+
+	if (cached_columns > 0)
+		return cached_columns;
 
 	if(!isatty(fd)) {
-		return default_notty;
+		cached_columns = default_notty;
+		return cached_columns;
 	}
 
 #if defined(TIOCGSIZE)
 	struct ttysize win;
 	if(ioctl(fd, TIOCGSIZE, &win) == 0) {
-		termwidth = win.ts_cols;
+		columns = win.ts_cols;
 	}
 #elif defined(TIOCGWINSZ)
 	struct winsize win;
 	if(ioctl(fd, TIOCGWINSZ, &win) == 0) {
-		termwidth = win.ws_col;
+		columns = win.ws_col;
 	}
 #endif
-	return termwidth == 0 ? default_tty : termwidth;
+
+	cached_columns = columns == 0 ? default_tty : columns;
+	return cached_columns;
 }
 
 /* does the same thing as 'rm -rf' */
diff --git a/src/pacman/util.h b/src/pacman/util.h
index e2297f8..d7f7b3c 100644
--- a/src/pacman/util.h
+++ b/src/pacman/util.h
@@ -49,6 +49,7 @@ int trans_init(alpm_transflag_t flags, int check_valid);
 int trans_release(void);
 int needs_root(void);
 int check_syncdbs(size_t need_repos, int check_valid);
+void columns_reset(int signum);
 unsigned short getcols(int fd);
 int rmrf(const char *path);
 void indentprint(const char *str, unsigned short indent, unsigned short cols);
-- 
1.8.4.2