Merge lp:~mapreri/libeatmydata/1556410 into lp:libeatmydata

[Mattia Rizzolo]

[Mattia Rizzolo (mapreri)]

I forgot, the author of the patch is Samuel Thibault <email address hidden>... maybe you want to credit him somewhere (I should have added it to the commit message, maybe)

[Mattia Rizzolo (mapreri)]

Forwarded again on https://github.com/stewartsmith/libeatmydata/pull/20

[Mattia Rizzolo (mapreri)]

(Please reject this, it seems as if I don't have the ability to mark the MR as "reject".)

[Stewart Smith (stewart)]

Cheers - I'll have a look on github. It turns out it's been a while since I looked at Launchpad.

Unmerged revisions

106. By Mattia Rizzolo on 2016-03-12

Use a weak reference to pthread_testcancel, so that it's called only if the program itself pulls libpthread

This avoid an hard link on pthread.

libeatmydata is linked against libpthread. This thus pulls libpthread
in all processes run under eatmydata. It happens that having
libpthread in a process makes pthread_mutex_lock() and all such basic
performance-sensitive operations much heavier (since they then have to
deal with potential multithreading). This avoids that by using a weak reference
to pthread_testcancel, so that pthread_testcancel is called only if the program
itself pulls libpthread.

LP: #1556410

=== modified file 'Makefile.am'
--- Makefile.am	2014-10-29 22:54:17 +0000
+++ Makefile.am	2016-03-12 11:42:21 +0000
@@ -80,7 +80,7 @@
   $(NO_WERROR) \
 	-DBUILDING_LIBEATMYDATA
 
-libeatmydata_la_LIBADD = $(LIBDL_LIBS) -lpthread
+libeatmydata_la_LIBADD = $(LIBDL_LIBS)
 libeatmydata_la_LDFLAGS = $(AM_LDFLAGS) -avoid-version
 
 #install-exec-hook:

=== modified file 'libeatmydata/libeatmydata.c'
--- libeatmydata/libeatmydata.c	2014-10-29 22:32:44 +0000
+++ libeatmydata/libeatmydata.c	2016-03-12 11:42:21 +0000
@@ -67,6 +67,7 @@
         libc_##name = (libc_##name##_##t)(intptr_t)dlsym(RTLD_NEXT, #name);			\
 						   dlerror();
 
+#pragma weak pthread_testcancel
 
 int LIBEATMYDATA_API msync(void *addr, size_t length, int flags);
 static int initing = 0;
@@ -113,7 +114,8 @@
 int LIBEATMYDATA_API fsync(int fd)
 {
 	if (eatmydata_is_hungry()) {
-		pthread_testcancel();
+		if (pthread_testcancel)
+			pthread_testcancel();
 		errno= 0;
 		return 0;
 	}
@@ -188,7 +190,8 @@
 int LIBEATMYDATA_API fdatasync(int fd)
 {
 	if (eatmydata_is_hungry()) {
-		pthread_testcancel();
+		if (pthread_testcancel)
+			pthread_testcancel();
 		errno= 0;
 		return 0;
 	}
@@ -199,7 +202,8 @@
 int LIBEATMYDATA_API msync(void *addr, size_t length, int flags)
 {
 	if (eatmydata_is_hungry()) {
-		pthread_testcancel();
+		if (pthread_testcancel)
+			pthread_testcancel();
 		errno= 0;
 		return 0;
 	}
@@ -211,7 +215,8 @@
 int sync_file_range(int fd, off64_t offset, off64_t nbytes, unsigned int flags)
 {
 	if (eatmydata_is_hungry()) {
-		pthread_testcancel();
+		if (pthread_testcancel)
+			pthread_testcancel();
 		errno= 0;
 		return 0;
 	}