pager: introduce wait_for_pager

Since f67b45f862 (Introduce trivial new pager.c helper infrastructure,
2006-02-28) we have the machinery to send our output to a pager.

That machinery, once set up, does not allow us to regain the original
stdio streams.

In the interactive commands (i.e.: add -p) we want to use the pager for
some output, while maintaining the interaction with the user.

Modify the pager machinery so that we can use `setup_pager()` and, once
we've finished sending the desired output for the pager, wait for the
pager termination using a new function `wait_for_pager()`.  Make this
function reset the pager machinery before returning.

One specific point to note is that we avoid forking the pager in
`setup_pager()` if the configured pager is an empty string [*1*] or
simply "cat" [*2*].  In these cases, `setup_pager()` does nothing and
therefore `wait_for_pager()` should not be called.

We could modify `setup_pager()` to return an indication of these
situations, so we could avoid calling `wait_for_pager()`.

However, let's avoid transferring that responsibility to the caller and
instead treat the call to `wait_for_pager()` as a no-op when we know we
haven't forked the pager.

   1.- 402461aab1 (pager: do not fork a pager if PAGER is set to empty.,
                   2006-04-16)

   2.- caef71a535 (Do not fork PAGER=cat, 2006-04-16)

Signed-off-by: Rubén Justo <rjusto@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/pager.c b/pager.c
index 251adfc2ade9f76c8b7c75a9eea772c77a8d5566..896f40fcd24c8ec4e8856496bebd5095b3e6ee64 100644 (file)
--- a/pager.c
+++ b/pager.c
@@ -14,7 +14,7 @@ int pager_use_color = 1;
 
 static struct child_process pager_process;
 static char *pager_program;
-static int close_fd2;
+static int old_fd1 = -1, old_fd2 = -1;
 
 /* Is the value coming back from term_columns() just a guess? */
 static int term_columns_guessed;
@@ -24,11 +24,11 @@ static void close_pager_fds(void)
 {
        /* signal EOF to pager */
        close(1);
-       if (close_fd2)
+       if (old_fd2 != -1)
                close(2);
 }
 
-static void wait_for_pager_atexit(void)
+static void finish_pager(void)
 {
        fflush(stdout);
        fflush(stderr);
@@ -36,8 +36,37 @@ static void wait_for_pager_atexit(void)
        finish_command(&pager_process);
 }
 
+static void wait_for_pager_atexit(void)
+{
+       if (old_fd1 == -1)
+               return;
+
+       finish_pager();
+}
+
+void wait_for_pager(void)
+{
+       if (old_fd1 == -1)
+               return;
+
+       finish_pager();
+       sigchain_pop_common();
+       unsetenv("GIT_PAGER_IN_USE");
+       dup2(old_fd1, 1);
+       close(old_fd1);
+       old_fd1 = -1;
+       if (old_fd2 != -1) {
+               dup2(old_fd2, 2);
+               close(old_fd2);
+               old_fd2 = -1;
+       }
+}
+
 static void wait_for_pager_signal(int signo)
 {
+       if (old_fd1 == -1)
+               return;
+
        close_pager_fds();
        finish_command_in_signal(&pager_process);
        sigchain_pop(signo);
@@ -113,6 +142,7 @@ void prepare_pager_args(struct child_process *pager_process, const char *pager)
 
 void setup_pager(void)
 {
+       static int once = 0;
        const char *pager = git_pager(isatty(1));
 
        if (!pager)
@@ -142,16 +172,20 @@ void setup_pager(void)
                die("unable to execute pager '%s'", pager);
 
        /* original process continues, but writes to the pipe */
+       old_fd1 = dup(1);
        dup2(pager_process.in, 1);
        if (isatty(2)) {
-               close_fd2 = 1;
+               old_fd2 = dup(2);
                dup2(pager_process.in, 2);
        }
        close(pager_process.in);
 
-       /* this makes sure that the parent terminates after the pager */
        sigchain_push_common(wait_for_pager_signal);
-       atexit(wait_for_pager_atexit);
+
+       if (!once) {
+               once++;
+               atexit(wait_for_pager_atexit);
+       }
 }
 
 int pager_in_use(void)

diff --git a/pager.h b/pager.h
index b77433026dc7a338a496db0b3b8b6ea5eac1770e..103ecac476fdd6523930d7ff8fe542eeec038438 100644 (file)
--- a/pager.h
+++ b/pager.h
@@ -5,6 +5,7 @@ struct child_process;
 
 const char *git_pager(int stdout_is_tty);
 void setup_pager(void);
+void wait_for_pager(void);
 int pager_in_use(void);
 int term_columns(void);
 void term_clear_line(void);