[PATCH 1/5] xfdopen(): if first attempt fails, free memory and try again

[Michael Haggerty <mhagger@alum.mit.edu>]

One likely reason for the failure of fdopen() is a lack of free
memory.

Also expose a new function, fdopen_with_retry(), which retries on
ENOMEM but doesn't die() on errors. In a moment this function will be
used elsewhere.

Suggested-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 git-compat-util.h | 11 +++++++++++
 wrapper.c         | 28 +++++++++++++++++++++++++---
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/git-compat-util.h b/git-compat-util.h
index 3455c5e..a5652a7 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -672,7 +672,18 @@ extern ssize_t xread(int fd, void *buf, size_t len);
 extern ssize_t xwrite(int fd, const void *buf, size_t len);
 extern ssize_t xpread(int fd, void *buf, size_t len, off_t offset);
 extern int xdup(int fd);
+
+/*
+ * Like fdopen(), but if the first attempt fails with ENOMEM, try to
+ * free up some memory and try again.
+ */
+extern FILE *fdopen_with_retry(int fd, const char *mode);
+
+/*
+ * Like fdopen_with_retry(), but die on errors.
+ */
 extern FILE *xfdopen(int fd, const char *mode);
+
 extern int xmkstemp(char *template);
 extern int xmkstemp_mode(char *template, int mode);
 extern int odb_mkstemp(char *template, size_t limit, const char *pattern);
diff --git a/wrapper.c b/wrapper.c
index d5a6cef..b60cc03 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -311,14 +311,36 @@ int xdup(int fd)
 	return ret;
 }
 
-FILE *xfdopen(int fd, const char *mode)
+FILE *fdopen_with_retry(int fd, const char *mode)
 {
 	FILE *stream = fdopen(fd, mode);
-	if (stream == NULL)
-		die_errno("Out of memory? fdopen failed");
+
+	if (!stream && errno == ENOMEM) {
+		/*
+		 * Try to free up some memory, then try again. We
+		 * would prefer to use sizeof(FILE) here, but that is
+		 * not guaranteed to be defined (e.g., FILE might be
+		 * an incomplete type).
+		 */
+		try_to_free_routine(1000);
+		stream = fdopen(fd, mode);
+	}
+
 	return stream;
 }
 
+FILE *xfdopen(int fd, const char *mode)
+{
+	FILE *stream = fdopen_with_retry(fd, mode);
+
+	if (stream)
+		return stream;
+	else if (errno == ENOMEM)
+		die_errno("Out of memory? fdopen failed");
+	else
+		die_errno("fdopen failed");
+}
+
 int xmkstemp(char *template)
 {
 	int fd;
-- 
2.1.4