There was a strange bug when converting SharedStringMap to use shared
memory: on Android, some tests would fail because a pref wasn't set or
there was something wrong with an expected error message. The root
cause was that mapping ashmem with MAP_PRIVATE results in all zeroes
(see bug 1525803), but that was read as a valid SharedStringMap with
length 0.
To prevent any possible future issues like that, this patch adds a
nonzero magic number to the header. It fits into padding on 64-bit and
the cost of setting and checking it should be essentially free.
Depends on D26744
Differential Revision: https://phabricator.services.mozilla.com/D26745
--HG--
extra : moz-landing-system : lando
There was a strange bug when converting SharedStringMap to use shared
memory: on Android, some tests would fail because a pref wasn't set or
there was something wrong with an expected error message. The root
cause was that mapping ashmem with MAP_PRIVATE results in all zeroes
(see bug 1525803), but that was read as a valid SharedStringMap with
length 0.
To prevent any possible future issues like that, this patch adds a
nonzero magic number to the header. It fits into padding on 64-bit and
the cost of setting and checking it should be essentially free.
Depends on D26744
Differential Revision: https://phabricator.services.mozilla.com/D26745
--HG--
extra : moz-landing-system : lando
- modify line wrap up to 80 chars; (tw=80)
- modify size of tab to 2 chars everywhere; (sts=2, sw=2)
--HG--
extra : rebase_source : 7eedce0311b340c9a5a1265dc42d3121cc0f32a0
extra : amend_source : 9cb4ffdd5005f5c4c14172390dd00b04b2066cd7
This is based on the SharedStringMap that's currently used for shared memory
string bundles.
When the parent process is ready to launch its first content process, it
creates a snapshot of the current state of the preference database, maps that
as read-only, and shares it with each content process. Look-ups in the
snapshotted map are done entirely using data in the shared memory region. It
doesn't require any additional per-process state data.
MozReview-Commit-ID: BdTUhak7dmS
--HG--
extra : intermediate-source : 434106f1b75e3ba900912f261bd22a1b7f5c931d
extra : absorb_source : 647ad37590448ad3c1eb8eb512bf671f262fa96e
extra : source : 68bb03c63b3cee1d47cbddfd3abf919f5783c04b
extra : histedit_source : 2228a9f8395929f5072a3c5ebda6ae3221e4a62d
This is based on the SharedStringMap that's currently used for shared memory
string bundles.
When the parent process is ready to launch its first content process, it
creates a snapshot of the current state of the preference database, maps that
as read-only, and shares it with each content process. Look-ups in the
snapshotted map are done entirely using data in the shared memory region. It
doesn't require any additional per-process state data.
MozReview-Commit-ID: BdTUhak7dmS
--HG--
extra : source : 68bb03c63b3cee1d47cbddfd3abf919f5783c04b
This is based on the SharedStringMap that's currently used for shared memory
string bundles.
When the parent process is ready to launch its first content process, it
creates a snapshot of the current state of the preference database, maps that
as read-only, and shares it with each content process. Look-ups in the
snapshotted map are done entirely using data in the shared memory region. It
doesn't require any additional per-process state data.
MozReview-Commit-ID: BdTUhak7dmS
--HG--
extra : rebase_source : e7cb96dd52380f2ed2fbd79b4e157e4efab65cb0
extra : absorb_source : ed95ed85388875353458eb65e41727e606ebf097
This class implements a shared memory key-value store that fits into a single
memory mapped segment. All of the runtime data for its instances are stored in
the shared memory region, which means that memory overhead for each instance
in each process is only a few bytes.
Importantly, the key and value strings returned by this class are also
pointers into the shared memory region, which means that once an instance is
created, its memory cannot be unmapped until process shutdown.
For the uses I intend to put it to, this is a reasonable constraint. If we
need to use it for shorter-lived maps in the future, we can add an option to
return non-literal dependent strings that will be copied if they need to be
kept alive long term.
MozReview-Commit-ID: 5BwAaDsb7HS
--HG--
extra : rebase_source : b472fe628018f88a2c4d6b3de4b7143aeca55e14
extra : absorb_source : 5cdeb568cfd2b4a5a767191402e699e61e653b3b
