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The branch, master has been updated via 69b7dbc24b33a84912f9f6a2074f0b58c9d91e22 (commit) from eb1d8c852dfdba9b37838d2cf3fa047f6c37b76c (commit) Those revisions listed above that are new to this repository have not appeared on any other notification email; so we list those revisions in full, below. - Log ----------------------------------------------------------------- commit 69b7dbc24b33a84912f9f6a2074f0b58c9d91e22 Author: Dries Kimpe <[email protected]> Date: Thu Dec 12 16:40:11 2013 -0600 Move aesop docs to aesop repo ----------------------------------------------------------------------- Summary of changes: code/doc/Makefile.subdir | 2 - code/doc/aesop-pbranch-cancel.txt | 203 ------------------------------------- code/doc/aesop.txt | 68 ------------ 3 files changed, 0 insertions(+), 273 deletions(-) delete mode 100644 code/doc/aesop-pbranch-cancel.txt delete mode 100644 code/doc/aesop.txt Diff of changes: diff --git a/code/doc/Makefile.subdir b/code/doc/Makefile.subdir index 99535a2..2f3ca80 100644 --- a/code/doc/Makefile.subdir +++ b/code/doc/Makefile.subdir @@ -3,8 +3,6 @@ DIR := doc ASCIIDOCSRC += $(DIR)/test.txt \ $(DIR)/pipelining.txt \ $(DIR)/compiling-triton.txt \ - $(DIR)/aesop.txt \ - $(DIR)/aesop-pbranch-cancel.txt \ $(DIR)/fault-injection.txt include $(top_srcdir)/doc/security/Makefile.subdir diff --git a/code/doc/aesop-pbranch-cancel.txt b/code/doc/aesop-pbranch-cancel.txt deleted file mode 100644 index 712f5f2..0000000 --- a/code/doc/aesop-pbranch-cancel.txt +++ /dev/null @@ -1,203 +0,0 @@ -Aesop: how to cancel pbranches -============================== - -== Existing implementation: Oct. 2011 - -for some context, here is an example of how things are done currently -(this is a client doing an RPC): - -[source,c] ----- -pwait -{ - pbranch - { - ret = timer(); - /* if timer triggers, then cancel other branches */ - if(ret == SUCCESS) - aesop_cancel_branches_wait(); - } - pbranch - { - ret = recv(); - /* cancel other branches in any case except when we detect that - * another branch has already started cancelling. - */ - if(ret != CANCELLED) - aesop_cancel_branches_wait(); - } - pbranch - { - ret = send(); - /* cancel branches on send error except when we detect that another - * branch has already started cancelling. - */ - if(ret != CANCELLED && ret != SUCCESS) - aesop_cancel_branches_wait(); - } -} ----- - -The aesop_cancel_branches_wait() works by trying to cancel pbranches in -a loop (with a timer) until the pbranch count hits 1. It has to have a -loop because "signaling" the other pbranches is lossy; there is no -way to guarantee that a pbranch cancel will be honored. It might hit -a pbranch that isn't currently in a blocking call. - -Problems with the current implementation: - -* if two pbranches call cancel simultaneously, it will deadlock -* there are some race conditions re: if a pbranch will detect if it has been - cancelled or not -* the cancel implementation is kludgey and more expensive than it needs to - be because of the timer loop -* semantics are unclear, especially at the aesop resource level -* if the send happens to complete (successfully) after the recv completes, - due to network transport ordering issues, then the - aesop_cancel_branches_wait() call after the recv might be triggered too - early - -== New semantics - -=== Semantics of the aesop-level cancel: -* totally asynchronous (no longer blocks until pbranches exit) -* cancel signal to pbranch is guaranteed to be delivered exactly once -** will affect current resource operation (if present) or the next one to - be posted -** cancel status is cleared for a pbranch once it has impacted one blocking - resource call (so pbranch can issue blocking cleanup functions safely if - it needs to) -* cancel will return true if it succeeded in delivering the cancel request, - false if it detects that another pbranch *at the same scope or higher* - already issued a cancel -** it is Ok if a child pbranch already is already cancelled in its own - scope; just skip that one and return success anyway - -* caller can ignore cancel return code if it doesn't care (most codes will - not) -* illegal to call cancel from a lonely pbranch - -=== Semantics of the resource-level cancel function: -* totally asynchronous -* returns true if it delivered the cancel signal to the operation in - question (and the operation is guaranteed to return ECANCEL or - whatever is appropriate for the resource) -* returns false if it failed to cancel the operation in question -* cancel function can no longer issue op callback directly (this complicates - some possible deadlock scenarios) - -=== Aesop internal implementation details: -* serialize calls to cancel (so that only one pbranch will "win") -* set flag at the pwait level to indicate that the branches have been - cancelled (or return failure if flag already set) -* for each pbranch: -** atomically check for resource op id (and make sure no posts happen - concurrently) -*** if op id present, try resource cancel -**** if success, done -**** if fail, set flag in ctrl structure to say pbranch should cancel -*** if op id not present, set flag in ctrl structure to say pbranch should - cancel -** proceed recursively, setting flag in child pbranches in the same manner - -=== Semantics of the resource-level post functions: -* will have hook to check (and clear) parent ctrl structure cancel flag -* if detect that pbranch has cancelled, the post should immediately fail - with appropriate return code for resource - -=== Misc: -* provide helper functions is_cancelled() and clear_cancelled() so a pbranch - can check and clear it's cancelled status manually if it wants to -* One possible implementation idea is to treat child pwait blocks as - resources, so that they generate op ids and have a cancel function just - like a resource call. Might make the aesop code a little cleaner in - exchange for pushing some complexity elsewhere. Need to look at code to - see if this is worth doing or not. -* A possible extension to this document, would be to name each pbranch and - add the ability to cancel specific pbranches by name. Probably not that - hard to implement, but we don't have a clear use case yet. - -Example using new semantics: - -[source,c] ----- - -while(retry) -{ - /* the send and recv are grouped into a single function - * (do_communication) to make it clearer that we want both to complete - * before cancelling the timer. - * - * The aesop_cancel_branches() call is safe against race conditions, so - * neither pbranch has to check if it has been cancelled before - * initiating an aesop_cancel_branches() of its own. - */ - pwait - { - pbranch - { - ret = timer(); - aesop_cancel_branches(); - } - - pbranch - { - comm_ret = do_communication() - aesop_cancel_branches(); - } - } -} - - -do_communication() -{ - pwait - { - pbranch - { - recv_ret = recv(); - } - pbranch - { - send_ret = send(); - if(ret != SUCCESS) - aesop_cancel_branches(); - } - } - - return(whatever); -} - ----- - -Example resource cancel semantics: - -[source,c] ----- - -triton_ret_t resource_post(void) -{ - /* don't start op if we have a pending, undelivered cancel signal */ - if(test_and_clear_cancelled_state()) - return(ECANCELLED); - - /* do whatever .... */ -} - -triton_ret_t resource_cancel(op_id) -{ - /* lock to protect against post/callback/cancel races */ - - if(queued) - /* move to cancelled queue, return success */ - - if(callback already in progress) - /* return failure */ - - if(cant find operation) - /* return failure */ - -} - ----- - diff --git a/code/doc/aesop.txt b/code/doc/aesop.txt deleted file mode 100644 index 3158c82..0000000 --- a/code/doc/aesop.txt +++ /dev/null @@ -1,68 +0,0 @@ -Aesop -===== - -[WARNING] -This document is out of date, at least as of November 2012. This should be -moved to the aesop repository and updated, especially the list of resources. - -== Source files - -Aesop source and header files are named *.ae and *.hae, respectively. They -are used exactly like c source and header files, except that they support -additional constructs, such as the __blocking qualifier for functions and -the pwait and pbranch constructs. - -In addition, Aesop remote code (ie, RPC functions) can be found in .aer and -.haer functions. These source files support an additional __remote -qualifier for functions to be invoked via RPC. - -== Compilers - -The configure process produces two compilers in the maint/ directory. aecc -is a compiler for .ae files, and aercc is a compiler for .aer files. Both -are shell scripts that combine preprocessing, source translation, and -compilation into one step. - -== Resources - -Resources are the lowest level aesop components that present Aesop -compatible intefaces for managing concurrency. The current list of -resources includes: - -* file resource -** code/src/versioned-osd/prototype/file-resource -** provides a mapping of open, close, read, write etc. functions. It uses - a thread pool by default to implement nonblocking semantics. - -* Berkeley DB resource -** code/src/versioned-osd/prototype/bdb-resource -** provides a mapping of common Berkeley DB functions. It uses a thread - pool by default to implement nonblocking semantics. - -* socket resource -** code/src/common/resources/aesocket/ -** waits for a file descriptor to be ready for read or write operations. - It does not implement actual read or write calls; it is assumed that the - caller will use this resource in conjunction with nonblocking reads and - writes. It uses libev, which in turn uses epoll() on Linux. - -* timer resource -** code/src/common/resources/timer/ -** implements timers with millisecond resolution. The underlying - implementation uses libev. - -* scheduling resource -** code/src/common/resource/scheduling/ -** Implements various synchronization primitives, for example Aesop - equivalents for condition variables. - -* branch threader resource -** code/src/common/resource/branch-threader/ -** Proof of concept that allows the developer to manually allocate a thread - for particular aesop code blocks. - -== Test programs - -A variety of tests and/or examples for Aesop functionality can be found in -the code/src/aesop/parser/tests/blocking directory. These tests use a -dummy resource to demonstrate various language features. hooks/post-receive --