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shm-logging: implement i3-dump-log -f (follow) 

This changes the SHM log format, it doesn’t use 0-bytes to separate
entries anymore. Instead of using lots of printf() calls in i3-dump-log,
we now do precisely one big write().

So, to be clear: i3-dump-log and i3 both need to be upgraded.
Mismatching versions will lead to garbage output (no crashes of i3, just
garbage output).

The -f flag uses an inter-process pthread_cond_t in the shared memory
header to broadcast the arrival of new messages to all i3-dump-log
processes. This internally uses futexes and thus doesn’t even mean a
kernel call in most cases. inter-process pthread_cond_ts require NPTL
(the Native Posix Thread Library, introduce in Linux 2.6).
This commit is contained in:
Michael Stapelberg 2012-08-13 00:57:57 +02:00
parent 070a18e598
commit e68a8dd86c
4 changed files with 121 additions and 36 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

97
i3-dump-log/main.c
View File

@ -2,7 +2,7 @@
* vim:ts=4:sw=4:expandtab
*
* i3 - an improved dynamic tiling window manager
* © 2009-2011 Michael Stapelberg and contributors (see also: LICENSE)
* © 2009-2012 Michael Stapelberg and contributors (see also: LICENSE)
*
* i3-dump-log/main.c: Dumps the i3 SHM log to stdout.
*
@ -28,18 +28,47 @@
#include "shmlog.h"
#include <i3/ipc.h>
static uint32_t offset_next_write,
wrap_count;
static i3_shmlog_header *header;
static char *logbuffer,
*walk;
static int check_for_wrap(void) {
if (wrap_count == header->wrap_count)
return 0;
/* The log wrapped. Print the remaining content and reset walk to the top
* of the log. */
wrap_count = header->wrap_count;
write(STDOUT_FILENO, walk, ((logbuffer + header->offset_last_wrap) - walk));
walk = logbuffer + sizeof(i3_shmlog_header);
return 1;
}
static void print_till_end(void) {
check_for_wrap();
int n = write(STDOUT_FILENO, walk, ((logbuffer + header->offset_next_write) - walk));
if (n > 0) {
walk += n;
}
}
int main(int argc, char *argv[]) {
int o, option_index = 0;
bool verbose = false;
bool verbose = false,
follow = false;
static struct option long_options[] = {
{"version", no_argument, 0, 'v'},
{"verbose", no_argument, 0, 'V'},
{"follow", no_argument, 0, 'f'},
{"help", no_argument, 0, 'h'},
{0, 0, 0, 0}
};
char *options_string = "s:vVh";
char *options_string = "s:vfVh";
while ((o = getopt_long(argc, argv, options_string, long_options, &option_index)) != -1) {
if (o == 'v') {
@ -47,9 +76,11 @@ int main(int argc, char *argv[]) {
return 0;
} else if (o == 'V') {
verbose = true;
} else if (o == 'f') {
follow = true;
} else if (o == 'h') {
printf("i3-dump-log " I3_VERSION "\n");
printf("i3-dump-log [-s <socket>]\n");
printf("i3-dump-log [-f] [-s <socket>]\n");
return 0;
}
}
@ -90,45 +121,61 @@ int main(int argc, char *argv[]) {
struct stat statbuf;
int logbuffer_shm = shm_open(shmname, O_RDONLY, 0);
/* NB: While we must never read, we need O_RDWR for the pthread condvar. */
int logbuffer_shm = shm_open(shmname, O_RDWR, 0);
if (logbuffer_shm == -1)
err(EXIT_FAILURE, "Could not shm_open SHM segment for the i3 log (%s)", shmname);
if (fstat(logbuffer_shm, &statbuf) != 0)
err(EXIT_FAILURE, "stat(%s)", shmname);
char *logbuffer = mmap(NULL, statbuf.st_size, PROT_READ, MAP_SHARED, logbuffer_shm, 0);
/* NB: While we must never read, we need O_RDWR for the pthread condvar. */
logbuffer = mmap(NULL, statbuf.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, logbuffer_shm, 0);
if (logbuffer == MAP_FAILED)
err(EXIT_FAILURE, "Could not mmap SHM segment for the i3 log");
i3_shmlog_header *header = (i3_shmlog_header*)logbuffer;
header = (i3_shmlog_header*)logbuffer;
if (verbose)
printf("next_write = %d, last_wrap = %d, logbuffer_size = %d, shmname = %s\n",
header->offset_next_write, header->offset_last_wrap, header->size, shmname);
int chars;
char *walk = logbuffer + header->offset_next_write;
/* Skip the first line, it very likely is mangled. Not a problem, though,
* the log is chatty enough to have plenty lines left. */
while (*walk != '\0')
walk++;
walk = logbuffer + header->offset_next_write;
/* Print the oldest log lines. We use printf("%s") to stop on \0. */
while (walk < (logbuffer + header->offset_last_wrap)) {
chars = printf("%s", walk);
/* Shortcut: If there are two consecutive \0 bytes, this part of the
* buffer was never touched. To not call printf() for every byte of the
* buffer, we directly exit the loop. */
if (*walk == '\0' && *(walk+1) == '\0')
break;
walk += (chars > 0 ? chars : 1);
/* We first need to print old content in case there was at least one
* wrapping already. */
if (*walk != '\0') {
/* In case there was a write to the buffer already, skip the first
* old line, it very likely is mangled. Not a problem, though, the log
* is chatty enough to have plenty lines left. */
while (*walk != '\n')
walk++;
walk++;
}
/* In case there was no wrapping, this is a no-op, otherwise it prints the
* old lines. */
wrap_count = 0;
check_for_wrap();
/* Then start from the beginning and print the newer lines */
walk = logbuffer + sizeof(i3_shmlog_header);
while (walk < (logbuffer + header->offset_next_write)) {
chars = printf("%s", walk);
walk += (chars > 0 ? chars : 1);
print_till_end();
if (follow) {
/* Since pthread_cond_wait() expects a mutex, we need to provide one.
* To not lock i3 (that’s bad, mhkay?) we just define one outside of
* the shared memory. */
pthread_mutex_t dummy_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_lock(&dummy_mutex);
while (1) {
pthread_cond_wait(&(header->condvar), &dummy_mutex);
/* If this was not a spurious wakeup, print the new lines. */
if (header->offset_next_write != offset_next_write) {
offset_next_write = header->offset_next_write;
print_till_end();
}
}
}
return 0;

22
include/shmlog.h
View File

@ -12,11 +12,33 @@
#define _I3_SHMLOG_H
#include <stdint.h>
#include <pthread.h>
/*
* Header of the shmlog file. Used by i3/src/log.c and i3/i3-dump-log/main.c.
*
*/
typedef struct i3_shmlog_header {
/* Byte offset where the next line will be written to. */
uint32_t offset_next_write;
/* Byte offset where the last wrap occured. */
uint32_t offset_last_wrap;
/* The size of the logfile in bytes. Since the size is limited to 25 MiB
* an uint32_t is sufficient. */
uint32_t size;
/* wrap counter. We need it to reliably signal to clients that we just
* wrapped (clients cannot use offset_last_wrap because that might
* coincidentally be exactly the same as previously). Overflows can happen
* and don’t matter — clients use an equality check (==). */
uint32_t wrap_count;
/* pthread condvar which will be broadcasted whenever there is a new
* message in the log. i3-dump-log uses this to implement -f (follow, like
* tail -f) in an efficient way. */
pthread_cond_t condvar;
} i3_shmlog_header;
#endif

2
src/i3.mk
View File

@ -7,7 +7,7 @@ i3_SOURCES := $(filter-out $(i3_SOURCES_GENERATED),$(wildcard src/*.c)
i3_HEADERS_CMDPARSER := $(wildcard include/GENERATED_*.h)
i3_HEADERS := $(filter-out $(i3_HEADERS_CMDPARSER),$(wildcard include/*.h))
i3_CFLAGS = $(XCB_CFLAGS) $(XCB_KBD_CFLAGS) $(XCB_WM_CFLAGS) $(X11_CFLAGS) $(XCURSOR_CFLAGS) $(YAJL_CFLAGS) $(LIBEV_CFLAGS) $(PCRE_CFLAGS) $(LIBSN_CFLAGS)
i3_LIBS = $(XCB_LIBS) $(XCB_KBD_LIBS) $(XCB_WM_LIBS) $(X11_LIBS) $(XCURSOR_LIBS) $(YAJL_LIBS) $(LIBEV_LIBS) $(PCRE_LIBS) $(LIBSN_LIBS) -lm
i3_LIBS = $(XCB_LIBS) $(XCB_KBD_LIBS) $(XCB_WM_LIBS) $(X11_LIBS) $(XCURSOR_LIBS) $(YAJL_LIBS) $(LIBEV_LIBS) $(PCRE_LIBS) $(LIBSN_LIBS) -lm -lpthread
# When using clang, we use pre-compiled headers to speed up the build. With
# gcc, this actually makes the build slower.

36
src/log.c
View File

@ -20,6 +20,7 @@
#include <sys/mman.h>
#include <sys/stat.h>
#include <errno.h>
#include <pthread.h>
#if defined(__APPLE__)
#include <sys/types.h>
#include <sys/sysctl.h>
@ -48,6 +49,8 @@ int shmlog_size = 0;
static char *logbuffer;
/* A pointer (within logbuffer) where data will be written to next. */
static char *logwalk;
/* A pointer to the shmlog header */
static i3_shmlog_header *header;
/* A pointer to the byte where we last wrapped. Necessary to not print the
* left-overs at the end of the ringbuffer. */
static char *loglastwrap;
@ -63,8 +66,6 @@ static int logbuffer_shm;
*
*/
static void store_log_markers(void) {
i3_shmlog_header *header = (i3_shmlog_header*)logbuffer;
header->offset_next_write = (logwalk - logbuffer);
header->offset_last_wrap = (loglastwrap - logbuffer);
header->size = logbuffer_size;
@ -128,6 +129,18 @@ void init_logging(void) {
logbuffer = NULL;
return;
}
/* Initialize with 0-bytes, just to be sure… */
memset(logbuffer, '\0', logbuffer_size);
header = (i3_shmlog_header*)logbuffer;
pthread_condattr_t cond_attr;
pthread_condattr_init(&cond_attr);
if (pthread_condattr_setpshared(&cond_attr, PTHREAD_PROCESS_SHARED) != 0)
ELOG("pthread_condattr_setpshared() failed, i3-dump-log -f will not work!\n");
pthread_cond_init(&(header->condvar), &cond_attr);
logwalk = logbuffer + sizeof(i3_shmlog_header);
loglastwrap = logbuffer + logbuffer_size;
store_log_markers();
@ -199,22 +212,25 @@ static void vlog(const bool print, const char *fmt, va_list args) {
fprintf(stderr, "BUG: single log message > 4k\n");
}
/* If there is no space for the current message (plus trailing
* nullbyte) in the ringbuffer, we need to wrap and write to the
* beginning again. */
if ((len+1) >= (logbuffer_size - (logwalk - logbuffer))) {
/* If there is no space for the current message in the ringbuffer, we
* need to wrap and write to the beginning again. */
if (len >= (logbuffer_size - (logwalk - logbuffer))) {
loglastwrap = logwalk;
logwalk = logbuffer + sizeof(i3_shmlog_header);
store_log_markers();
header->wrap_count++;
}
/* Copy the buffer, terminate it, move the write pointer to the byte after
* our current message. */
/* Copy the buffer, move the write pointer to the byte after our
* current message. */
strncpy(logwalk, message, len);
logwalk[len] = '\0';
logwalk += len + 1;
logwalk += len;
store_log_markers();
/* Wake up all (i3-dump-log) processes waiting for condvar. */
pthread_cond_broadcast(&(header->condvar));
if (print)
fwrite(message, len, 1, stdout);
}