release_handler底层指令 热部署的实际执行者

下面的指令是热部署干活的指令：

%%-----------------------------------------------------------------
%% An unpurged module is a module for which there exist an old
%% version of the code.  This should only be the case if there are
%% processes running the old version of the code.
%%
%% This functions evaluates each instruction.  Note that the
%% instructions here are low-level instructions.  e.g. lelle's
%% old synchronized_change would be translated to
%%   {load_object_code, Modules},
%%   {suspend, Modules}, [{load, Module}],
%%   {resume, Modules}, {purge, Modules}
%% Or, for example, if we want to do advanced external code change
%% on two modules that depend on each other, by killing them and
%% then restaring them, we could do:
%%   {load_object_code, [Mod1, Mod2]},
%%   % delete old version
%%   {remove, {Mod1, brutal_purge}}, {remove, {Mod2, brutal_purge}},
%%   % now, some procs migth be running prev current (now old) version
%%   % kill them, and load new version
%%   {load, {Mod1, brutal_purge}}, {load, {Mod2, brutal_purge}}
%%   % now, there is one version of the code (new, current)
%%
%% NOTE: All load_object_code must be first in the script,
%%       a point_of_no_return must be present (if load_object_code
%%       is present).
%%
%% {load_object_code, {Lib, LibVsn, [Mod]}
%%    read the files as binarys. do not make code out of them
%% {load, {Module, PrePurgeMethod, PostPurgeMethod}}
%%    Module must have been load_object_code:ed.  make code out of it
%%    old procs && soft_purge => no new release
%%    old procs && brutal_purge => old procs killed
%%    The new old code will be gc:ed later on, if PostPurgeMethod =
%%    soft_purge.  If it is brutal_purge, the code is purged when
%%    the release is made permanent.
%% {remove, {Module, PrePurgeMethod, PostPurgeMethod}}
%%    make current version old.  no current left.
%%    old procs && soft_purge => no new release
%%    old procs && brutal_purge => old procs killed
%%    The new old code will be gc:ed later on, if PostPurgeMethod =
%%    soft_purge.  If it is brutal_purge, the code is purged when
%%    the release is made permanent.
%% {purge, Modules}
%%    kill all procs running old code, delete old code
%% {suspend, [Module | {Module, Timeout}]}
%%    If a process doesn't repsond - never mind.  It will be killed
%%    later on (if a purge is performed).
%%    Hmm, we must do something smart here... we should probably kill it,
%%    but we cant, because its supervisor will restart it directly!  Maybe
%%    we should keep a list of those, call supervisor:terminate_child()
%%    when all others are suspended, and call sup:restart_child() when the
%%    others are resumed.
%% {code_change, [{Module, Extra}]}
%% {code_change, Mode, [{Module, Extra}]}  Mode = up | down
%%    Send code_change only to suspended procs running this code
%% {resume, [Module]}
%%    resume all previously suspended processes
%% {stop, [Module]}
%%    stop all procs running this code
%% {start, [Module]}
%%    starts the procs that were previously stopped for this code.
%%    Note that this will start processes in exactly the same place
%%    in the suptree where there were procs previously.
%% {sync_nodes, Id, [Node]}
%% {sync_nodes, Id, {M, F, A}}
%%    Synchronizes with the Nodes (or apply(M,F,A) == Nodes).  All Nodes
%%    must also exectue the same line.  Waits for all these nodes to get
%%    to this line.
%% point_of_no_return
%% restart_new_emulator
%% {stop_application, Appl}     - Impl with apply
%% {unload_application, Appl}   - Impl with {remove..}
%% {load_application, Appl}     - Impl with {load..}
%% {start_application, Appl}    - Impl with apply
%%-----------------------------------------------------------------

见release_handler_1.erl, 指令不是很多，基本上是bif的封装。