Optimize shmlog writing:
Optimize shmlog writing:

If we know the record length, only hold the mutex while we reserve
the space.  Until we change the first byte, nothing bad can happen.

XXX: a memory barrier is strictly speaking necessary before we assign
the first byte.

If there are no '%' in the format string, treat as fixed length for
speed.



git-svn-id: 2c9807fa3ff65b17195bd55dc8a6c4261e10127b@895 d4fa192b-c00b-0410-8231-f00ffab90ce4

zhoualbeart/Varnish-Cache,mrhmouse/Varnish-Cache,zhoualbeart/Varnish-Cache,mrhmouse/Varnish-Cache,mrhmouse/Varnish-Cache,alarky/varnish-cache-doc-ja,gquintard/Varnish-Cache,alarky/varnish-cache-doc-ja,ambernetas/varnish-cache,feld/Varnish-Cache,gauthier-delacroix/Varnish-Cache,wikimedia/operations-debs-varnish,ssm/pkg-varnish,franciscovg/Varnish-Cache,wikimedia/operations-debs-varnish,alarky/varnish-cache-doc-ja,ambernetas/varnish-cache,drwilco/varnish-cache-drwilco,wikimedia/operations-debs-varnish,ambernetas/varnish-cache,ssm/pkg-varnish,feld/Varnish-Cache,drwilco/varnish-cache-drwilco,wikimedia/operations-debs-varnish,chrismoulton/Varnish-Cache,varnish/Varnish-Cache,mrhmouse/Varnish-Cache,chrismoulton/Varnish-Cache,drwilco/varnish-cache-drwilco,ajasty-cavium/Varnish-Cache,franciscovg/Varnish-Cache,gquintard/Varnish-Cache,franciscovg/Varnish-Cache,zhoualbeart/Varnish-Cache,drwilco/varnish-cache-old,zhoualbeart/Varnish-Cache,1HLtd/Varnish-Cache,ssm/pkg-varnish,zhoualbeart/Varnish-Cache,chrismoulton/Varnish-Cache,1HLtd/Varnish-Cache,ssm/pkg-varnish,gauthier-delacroix/Varnish-Cache,chrismoulton/Varnish-Cache,ssm/pkg-varnish,gauthier-delacroix/Varnish-Cache,ajasty-cavium/Varnish-Cache,varnish/Varnish-Cache,gquintard/Varnish-Cache,gauthier-delacroix/Varnish-Cache,varnish/Varnish-Cache,feld/Varnish-Cache,franciscovg/Varnish-Cache,ajasty-cavium/Varnish-Cache,alarky/varnish-cache-doc-ja,1HLtd/Varnish-Cache,alarky/varnish-cache-doc-ja,gauthier-delacroix/Varnish-Cache,gquintard/Varnish-Cache,franciscovg/Varnish-Cache,varnish/Varnish-Cache,drwilco/varnish-cache-old,1HLtd/Varnish-Cache,ajasty-cavium/Varnish-Cache,varnish/Varnish-Cache,chrismoulton/Varnish-Cache,drwilco/varnish-cache-old,ajasty-cavium/Varnish-Cache,mrhmouse/Varnish-Cache,feld/Varnish-Cache,wikimedia/operations-debs-varnish,feld/Varnish-Cache