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258 lines
8.4 KiB
C
258 lines
8.4 KiB
C
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/*
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** prshm.h -- NSPR Shared Memory
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**
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** NSPR Named Shared Memory API provides a cross-platform named
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** shared-memory interface. NSPR Named Shared Memory is modeled on
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** similar constructs in Unix and Windows operating systems. Shared
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** memory allows multiple processes to access one or more common shared
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** memory regions, using it as an inter-process communication channel.
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**
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** Notes on Platform Independence:
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** NSPR Named Shared Memory is built on the native services offered
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** by most platforms. The NSPR Named Shared Memory API tries to
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** provide a least common denominator interface so that it works
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** across all supported platforms. To ensure that it works everywhere,
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** some platform considerations must be accomodated and the protocol
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** for using NSPR Shared Memory API must be observed.
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**
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** Protocol:
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** Multiple shared memories can be created using NSPR's Shared Memory
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** feature. For each named shared memory, as defined by the name
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** given in the PR_OpenSharedMemory() call, a protocol for using the
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** shared memory API is required to ensure desired behavior. Failing
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** to follow the protocol may yield unpredictable results.
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**
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** PR_OpenSharedMemory() will create the shared memory segment, if it
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** does not already exist, or open a connection that the existing
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** shared memory segment if it already exists.
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**
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** PR_AttachSharedMemory() should be called following
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** PR_OpenSharedMemory() to map the memory segment to an address in
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** the application's address space.
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**
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** PR_AttachSharedMemory() may be called to re-map a shared memory
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** segment after detaching the same PRSharedMemory object. Be
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** sure to detach it when done.
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**
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** PR_DetachSharedMemory() should be called to un-map the shared
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** memory segment from the application's address space.
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**
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** PR_CloseSharedMemory() should be called when no further use of the
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** PRSharedMemory object is required within a process. Following a
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** call to PR_CloseSharedMemory() the PRSharedMemory object is
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** invalid and cannot be reused.
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**
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** PR_DeleteSharedMemory() should be called before process
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** termination. After calling PR_DeleteSharedMemory() any further use
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** of the shared memory associated with the name may cause
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** unpredictable results.
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**
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** Files:
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** The name passed to PR_OpenSharedMemory() should be a valid filename
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** for a unix platform. PR_OpenSharedMemory() creates file using the
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** name passed in. Some platforms may mangle the name before creating
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** the file and the shared memory.
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**
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** The unix implementation may use SysV IPC shared memory, Posix
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** shared memory, or memory mapped files; the filename may used to
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** define the namespace. On Windows, the name is significant, but
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** there is no file associated with name.
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**
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** No assumptions about the persistence of data in the named file
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** should be made. Depending on platform, the shared memory may be
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** mapped onto system paging space and be discarded at process
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** termination.
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**
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** All names provided to PR_OpenSharedMemory() should be valid
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** filename syntax or name syntax for shared memory for the target
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** platform. Referenced directories should have permissions
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** appropriate for writing.
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**
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** Limits:
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** Different platforms have limits on both the number and size of
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** shared memory resources. The default system limits on some
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** platforms may be smaller than your requirements. These limits may
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** be adjusted on some platforms either via boot-time options or by
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** setting the size of the system paging space to accomodate more
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** and/or larger shared memory segment(s).
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**
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** Security:
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** On unix platforms, depending on implementation, contents of the
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** backing store for the shared memory can be exposed via the file
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** system. Set permissions and or access controls at create and attach
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** time to ensure you get the desired security.
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**
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** On windows platforms, no special security measures are provided.
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**
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** Example:
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** The test case pr/tests/nameshm1.c provides an example of use as
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** well as testing the operation of NSPR's Named Shared Memory.
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**
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** lth. 18-Aug-1999.
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*/
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#ifndef prshm_h___
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#define prshm_h___
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#include "prtypes.h"
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#include "prio.h"
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PR_BEGIN_EXTERN_C
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/*
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** Declare opaque type PRSharedMemory.
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*/
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typedef struct PRSharedMemory PRSharedMemory;
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/*
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** FUNCTION: PR_OpenSharedMemory()
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**
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** DESCRIPTION:
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** PR_OpenSharedMemory() creates a new shared-memory segment or
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** associates a previously created memory segment with name.
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**
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** When parameter create is (PR_SHM_EXCL | PR_SHM_CREATE) and the
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** shared memory already exists, the function returns NULL with the
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** error set to PR_FILE_EXISTS_ERROR.
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**
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** When parameter create is PR_SHM_CREATE and the shared memory
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** already exists, a handle to that memory segment is returned. If
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** the segment does not exist, it is created and a pointer to the
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** related PRSharedMemory structure is returned.
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**
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** When parameter create is 0, and the shared memory exists, a
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** pointer to a PRSharedMemory is returned. If the shared memory does
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** not exist, NULL is returned with the error set to
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** PR_FILE_NOT_FOUND_ERROR.
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**
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** INPUTS:
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** name -- the name the shared-memory segment is known as.
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** size -- the size of the shared memory segment.
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** flags -- Options for creating the shared memory
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** mode -- Same as is passed to PR_Open()
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**
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** OUTPUTS:
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** The shared memory is allocated.
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**
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** RETURNS: Pointer to opaque structure PRSharedMemory or NULL.
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** NULL is returned on error. The reason for the error can be
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** retrieved via PR_GetError() and PR_GetOSError();
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**
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*/
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NSPR_API( PRSharedMemory * )
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PR_OpenSharedMemory(
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const char *name,
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PRSize size,
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PRIntn flags,
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PRIntn mode
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);
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/* Define values for PR_OpenShareMemory(...,create) */
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#define PR_SHM_CREATE 0x1 /* create if not exist */
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#define PR_SHM_EXCL 0x2 /* fail if already exists */
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/*
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** FUNCTION: PR_AttachSharedMemory()
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**
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** DESCRIPTION:
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** PR_AttachSharedMemory() maps the shared-memory described by
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** shm to the current process.
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**
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** INPUTS:
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** shm -- The handle returned from PR_OpenSharedMemory().
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** flags -- options for mapping the shared memory.
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** PR_SHM_READONLY causes the memory to be attached
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** read-only.
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**
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** OUTPUTS:
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** On success, the shared memory segment represented by shm is mapped
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** into the process' address space.
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**
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** RETURNS: Address where shared memory is mapped, or NULL.
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** NULL is returned on error. The reason for the error can be
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** retrieved via PR_GetError() and PR_GetOSError();
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**
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**
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*/
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NSPR_API( void * )
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PR_AttachSharedMemory(
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PRSharedMemory *shm,
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PRIntn flags
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);
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/* Define values for PR_AttachSharedMemory(...,flags) */
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#define PR_SHM_READONLY 0x01
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/*
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** FUNCTION: PR_DetachSharedMemory()
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**
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** DESCRIPTION:
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** PR_DetachSharedMemory() detaches the shared-memory described
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** by shm.
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**
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** INPUTS:
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** shm -- The handle returned from PR_OpenSharedMemory().
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** addr -- The address at which the memory was attached.
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**
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** OUTPUTS:
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** The shared memory mapped to an address via a previous call to
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** PR_AttachSharedMemory() is unmapped.
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**
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** RETURNS: PRStatus
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**
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*/
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NSPR_API( PRStatus )
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PR_DetachSharedMemory(
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PRSharedMemory *shm,
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void *addr
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);
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/*
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** FUNCTION: PR_CloseSharedMemory()
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**
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** DESCRIPTION:
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** PR_CloseSharedMemory() closes the shared-memory described by
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** shm.
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**
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** INPUTS:
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** shm -- The handle returned from PR_OpenSharedMemory().
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**
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** OUTPUTS:
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** the shared memory represented by shm is closed
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**
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** RETURNS: PRStatus
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**
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*/
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NSPR_API( PRStatus )
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PR_CloseSharedMemory(
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PRSharedMemory *shm
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);
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/*
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** FUNCTION: PR_DeleteSharedMemory()
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**
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** DESCRIPTION:
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** The shared memory resource represented by name is released.
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**
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** INPUTS:
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** name -- the name the shared-memory segment
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**
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** OUTPUTS:
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** depending on platform, resources may be returned to the underlying
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** operating system.
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**
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** RETURNS: PRStatus
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**
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*/
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NSPR_API( PRStatus )
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PR_DeleteSharedMemory(
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const char *name
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);
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PR_END_EXTERN_C
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#endif /* prshm_h___ */
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