Re: Why sourcing a file is not faster than doing a loop with eval, zle -N

[Peter Stephenson <p.w.stephenson@ntlworld.com>]

On Mon, 19 Jun 2017 17:16:01 +0100
Stephane Chazelas <stephane.chazelas@gmail.com> wrote:
> That defeats a benefit of stdio saving read() systems calls by
> reading in chunk if we end up doing one system call per byte
> anyway.

Yes, if it's line buffered we should ideally only be unblocking
interrupts once around reading the line, which will dominate the
timing.

How about something like this?  As far as I can tell, fgets is designed
from the ground up as Gets Done Properly, so if you have it on your
system it will work correctly.  I can't think of a case where this
wouldn't do the right thing --- fgets will read at most one line and if
it does we were going to get the big STDIO overhead at that point
anyway.

pws

diff --git a/Src/input.c b/Src/input.c
index 92abaec..03d6476 100644
--- a/Src/input.c
+++ b/Src/input.c
@@ -147,6 +147,53 @@ shingetline(void)
     for (;;) {
 	winch_unblock();
 	dont_queue_signals();
+#ifdef HAVE_FGETS
+	do {
+	    errno = 0;
+	    p = fgets(buf, BUFSIZ, bshin);
+	} while (!p && errno == EINTR);
+	winch_block();
+	if (!p) {
+	    restore_queue_signals(q);
+	    return NULL;
+	}
+	c = 0;
+	while (*p) {
+	    if (imeta(STOUC(*p++)))
+		c++;
+	}
+	if (p > buf) {
+	    /* p is pointing to '\0' */
+	    ptrdiff_t nread = p - buf;
+	    queue_signals();
+	    line = zrealloc(line, ll + c + nread + 1);
+	    if (c) {
+		char *dest = line + ll;
+		char *src = buf;
+		while (src < p) {
+		    if (imeta(STOUC(*src))) {
+			*dest++ = Meta;
+			*dest++ = STOUC(*src++) ^ 32;
+		    } else
+			*dest++ = *src++;
+		}
+		*dest++ = '\0';
+	    } else {
+		/* copy null */
+		memcpy(line + ll, buf, nread + 1);
+	    }
+	    unqueue_signals();
+	    /* fgets stops at first newline but stores '\0' after */
+	    if (p[-1] == '\n') {
+		restore_queue_signals(q);
+		return line;
+	    }
+	    ll += nread;
+	} else {
+	    restore_queue_signals(q);
+	    return NULL;
+	}
+#else
 	do {
 	    errno = 0;
 	    c = fgetc(bshin);
@@ -178,6 +225,7 @@ shingetline(void)
 	    p = buf;
 	    unqueue_signals();
 	}
+#endif
     }
 }
 
diff --git a/configure.ac b/configure.ac
index 88da89e..2f19a73 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1325,7 +1325,8 @@ AC_CHECK_FUNCS(strftime strptime mktime timelocal \
 	       cygwin_conv_path \
 	       nanosleep \
 	       srand_deterministic \
-	       setutxent getutxent endutxent getutent)
+	       setutxent getutxent endutxent getutent \
+	       fgets)
 AC_FUNC_STRCOLL
 
 AH_TEMPLATE([REALPATH_ACCEPTS_NULL],