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

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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
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36
src/log.c
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@ -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);
}