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/*
* %CopyrightBegin%
*
* Copyright Ericsson AB 2012-2016. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* %CopyrightEnd%
*/
/* Description:
* This is the interface that facilitates changing the beam code
* (load,upgrade,delete) while allowing executing Erlang processes to
* access the code without any locks or other expensive memory barriers.
*
* The basic idea is to maintain several "logical copies" of the code. These
* copies are identified by a global 'code index', an integer of 0, 1 or 2.
* The code index is used as argument to code access structures like
* export, module, beam_catches, beam_ranges.
*
* The current 'active' code index is used to access the current running
* code. The 'staging' code index is used by the process that performs
* a code change operation. When a code change operation completes
* succesfully, the staging code index becomes the new active code index.
*
* The third code index is not explicitly used. It can be thought of as
* the "previous active" or the "next staging" index. It is needed to make
* sure that we do not reuse a code index for staging until we are sure
* that no executing BIFs are still referencing it.
* We could get by with only two (0 and 1), but that would require that we
* must wait for all schedulers to re-schedule before each code change
* operation can start staging.
*
* Note that the 'code index' is very loosely coupled to the concept of
* 'current' and 'old' module versions. You can almost say that they are
* orthogonal to each other. Code index is an emulator global concept while
* 'current' and 'old' is specific for each module.
*/
#ifndef __CODE_IX_H__
#define __CODE_IX_H__
#ifndef __SYS_H__
# ifdef HAVE_CONFIG_H
# include "config.h"
# endif
# include "sys.h"
#endif
struct process;
#define ERTS_NUM_CODE_IX 3
typedef unsigned ErtsCodeIndex;
/* Called once at emulator initialization.
*/
void erts_code_ix_init(void);
/* Return active code index.
* Is guaranteed to be valid until the calling BIF returns.
* To get a consistent view of the code, only one call to erts_active_code_ix()
* should be made and the returned ix reused within the same BIF call.
*/
ERTS_GLB_INLINE
ErtsCodeIndex erts_active_code_ix(void);
/* Return staging code ix.
* Only used by a process performing code loading/upgrading/deleting/purging.
* Code write permission must be seized.
*/
ERTS_GLB_INLINE
ErtsCodeIndex erts_staging_code_ix(void);
/* Try seize exclusive code write permission. Needed for code staging.
* Main process lock (only) must be held.
* System thread progress must not be blocked.
* Caller must not already hold the code write permission.
* Caller is suspended and *must* yield if 0 is returned.
*/
int erts_try_seize_code_write_permission(struct process* c_p);
/* Release code write permission.
* Will resume any suspended waiters.
*/
void erts_release_code_write_permission(void);
/* Prepare the "staging area" to be a complete copy of the active code.
* Code write permission must have been seized.
* Must be followed by calls to either "end" and "commit" or "abort" before
* code write permission can be released.
*/
void erts_start_staging_code_ix(int num_new);
/* End the staging.
* Preceded by "start" and must be followed by "commit".
*/
void erts_end_staging_code_ix(void);
/* Set staging code index as new active code index.
* Preceded by "end".
*/
void erts_commit_staging_code_ix(void);
/* Abort the staging.
* Preceded by "start".
*/
void erts_abort_staging_code_ix(void);
#ifdef ERTS_ENABLE_LOCK_CHECK
int erts_has_code_write_permission(void);
#endif
#if ERTS_GLB_INLINE_INCL_FUNC_DEF
extern erts_smp_atomic32_t the_active_code_index;
extern erts_smp_atomic32_t the_staging_code_index;
ERTS_GLB_INLINE ErtsCodeIndex erts_active_code_ix(void)
{
return erts_smp_atomic32_read_nob(&the_active_code_index);
}
ERTS_GLB_INLINE ErtsCodeIndex erts_staging_code_ix(void)
{
return erts_smp_atomic32_read_nob(&the_staging_code_index);
}
#endif /* ERTS_GLB_INLINE_INCL_FUNC_DEF */
#endif /* !__CODE_IX_H__ */
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