RCRegion.h

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//-*-c++-*-
#ifdef PLATFORM_APERIOS
#  include <OPENR/RCRegion.h>
#else
#  ifndef INCLUDED_RCRegion_h_
#  define INCLUDED_RCRegion_h_

#include "Shared/ReferenceCounter.h"
#include "ProcessID.h"
#include "IPC/Thread.h"
#include <sys/types.h>
#include <cstdio>
#include <map>
#include <exception>

/* Do you want to use the SysV shared memory call interface
 * or the POSIX shared memory interface?  They have different
 * strengths/weaknesses on different platforms... :-/    */

/*! @def POSIX_SHM
 *  @brief If TEKKOTSU_SHM_STYLE is set to POSIX_SHM, POSIX style shared memory will be used (shm_open, shm_unlink, mmap, munmap, ...);
 *  This is the default shared memory interface, both portable and stable.  By default, regular open() and unlink()
 *  will be used to implement the regions using file-backed shared memory.  If you define USE_UNBACKED_SHM,
 *  RCRegion will use shm_open/shm_unlink instead.  Unbacked shared memory is nice because there's no
 *  interaction with your filesystem, but isn't quite as portable.  (Cygwin didn't seem to like it too much...) */

/*! @def SYSV_SHM
 *  @brief If TEKKOTSU_SHM_STYLE is set to SYSV_SHM, SysV style shared memory will be used (shmget, shmctl, shmat, shmdt, ...)
 *  SysV style seems to stick around following a program crash, and can't be unlinked pre-emptively while still in use.
 *  Since it appears many systems also limit the number of shared memory regions (via a sysctl configuration), leaking
 *  regions following repeated crashes during development gets annoying. */

/*! @def NO_SHM
 *  @brief If TEKKOTSU_SHM_STYLE is set to NO_SHM, all shared memory operations become straight new/delete's; this restricts the program to using threads in a single process */

/*! @def TEKKOTSU_SHM_STYLE
 *  @brief Can be set to one of POSIX_SHM, SYSV_SHM, or NO_SHM */

#ifndef POSIX_SHM
#  define POSIX_SHM 1
#endif
#ifndef SYSV_SHM
#  define SYSV_SHM 2
#endif
#ifndef NO_SHM
#  define NO_SHM 3
#endif
#ifndef TEKKOTSU_SHM_STYLE
#  define TEKKOTSU_SHM_STYLE NO_SHM
#endif

#if TEKKOTSU_SHM_STYLE!=SYSV_SHM && TEKKOTSU_SHM_STYLE!=POSIX_SHM && TEKKOTSU_SHM_STYLE!=NO_SHM
#  error Unknown TEKKOTSU_SHM_STYLE setting
#endif

#if TEKKOTSU_SHM_STYLE==POSIX_SHM
namespace plist { template<class T> class Primitive; }
#endif

//! provides compatability with the OPEN-R type of the same name
class RCRegion {
public:

  // The type of region Identifier depends on the style of shared memory being used

#if TEKKOTSU_SHM_STYLE==SYSV_SHM
  //! contains all information needed to attach this region from a different process
  struct Identifier {
    Identifier() : key(), shmid(), size(0) {}
    key_t key; //!< key_t is defined by system headers, contains system region info
    int shmid; //!< an integer key value which identifies the region
    size_t size; //!< the size of the region
  };

#elif TEKKOTSU_SHM_STYLE==POSIX_SHM || TEKKOTSU_SHM_STYLE==NO_SHM
  //! maximum guaranteed length for users' region names (might have a little leeway depending on process ID prefix or tmp path prefix)
  static const unsigned int MAX_NAME_LEN=64;

  //! contains all information needed to attach this region from a different process
  struct Identifier {
    Identifier() : size(0) {} //!< constructor
    char key[MAX_NAME_LEN]; //!< a string name for the key
    size_t size; //!< size of the region
  };

#  if TEKKOTSU_SHM_STYLE==POSIX_SHM
#    ifndef USE_UNBACKED_SHM
  static plist::Primitive<std::string> shmRoot; //!< determines location of the file backing within file system
#    endif
  static plist::Primitive<bool> useUniqueMemoryRegions; //!< if true, prefixes region names with #rootPID
  static pid_t rootPID; //!< this is the pid of the original process, used for unique names of memory regions; pid_t is from sys/types.h
#  endif
#endif


  // The constructors, offering either an Aperios-compatable version,
  // or a linux-specific version offering explicit control over the
  // key value, aids better debugging

#if TEKKOTSU_SHM_STYLE==SYSV_SHM
  //! constructor (OPEN-R compatability)
  explicit RCRegion(size_t sz)
    : id(), base(NULL), references(NULL)
  { init(sz,nextKey,true); }
  //! constructor, name isn't used for sysv-style shared memory (not OPEN-R compatable)
  /*! could hash the name to generate key...? */
  RCRegion(const std::string&, size_t sz)
    : id(), base(NULL), references(NULL)
  { init(sz,nextKey,true); }

#elif TEKKOTSU_SHM_STYLE==POSIX_SHM || TEKKOTSU_SHM_STYLE==NO_SHM
  //! constructor (OPEN-R compatability, name is autogenerated)
  explicit RCRegion(size_t sz)
    : id(), base(NULL), references(NULL)
  {
    char name[RCRegion::MAX_NAME_LEN];
    snprintf(name,RCRegion::MAX_NAME_LEN,"Rgn.%d.%u",ProcessID::getID(),static_cast<unsigned int>(++nextKey));
    name[RCRegion::MAX_NAME_LEN-1]='\0';
    init(sz,name,true);
  }
  //! constructor, specify your own name for better debugging accountability (not OPEN-R compatable)
  RCRegion(const std::string& name, size_t sz)
    : id(), base(NULL), references(NULL)
  { init(sz,name,true); }
#endif

  //! requests that a specified RCRegion be loaded into the current process's memory space
  static RCRegion * attach(const Identifier& rid);
  
  char * Base() const { return base; } //!< the pointer to the shared memory region
  size_t Size() const { return id.size; } //!< the size of the shared memory region
  static void setNextKey(key_t k) { nextKey=k; } //!< sets the next key to be used for automatic assignment to new regions
  static key_t getNextKey() { return nextKey+1; } //!< return the next region serial number -- doesn't actually increment it though, repeated calls will return the same value until the value is actually used
  const Identifier& ID() const { return id; } //!< returns the identifier of this region
  
  int NumberOfReference() const { return references[ProcessID::NumProcesses]; } //!< number of total references to this region, total of all processes
  int NumberOfLocalReference() const { return references[ProcessID::getID()]; } //!< number of references to the region from the current process (in the ProcessID threadgroup sense, not necessarily system-process)
  void AddReference(); //!< adds a reference from the current process
  void RemoveReference(); //!< removes a reference from the current process
  void AddSharedReference(); //!< adds a reference which is held by another shared memory region
  void RemoveSharedReference(); //!< removes a reference which is held by another shared memory region
  
  static void aboutToFork(ProcessID::ProcessID_t newID); //!< does housekeeping to mark the region as attached and the same number of references in the new process as well
  static void faultShutdown(); //!< try to unload all regions in a clean manner

#if TEKKOTSU_SHM_STYLE==SYSV_SHM
  //! a map from the shared memory key type to the actual region structure
  typedef std::map<key_t,RCRegion*> attachedRegions_t;
#elif TEKKOTSU_SHM_STYLE==POSIX_SHM || TEKKOTSU_SHM_STYLE==NO_SHM
  //! a map from the shared memory key type to the actual region structure
  typedef std::map<std::string,RCRegion*> attachedRegions_t;
#endif
  static unsigned int NumberOfAttach() { return attachedRegions.size(); } //!< returns the number of regions which are currently attached in the process
  
  //! Returns an iterator to the beginning of the attached regions mapping -- it->first is the key, it->second is the RCRegion*
  /*! If you need thread-safety (i.e. another thread may attach/detach while you are iterating), pass true, and be sure to use attachedAdvance() to increment the iterator!
   *  This doesn't prevent other threads from attaching/detaching regions, it only prevents detaching the one you're on.
   *  When you're done with a thread-safe iterator, either attachedAdvance() it off the end, or manually call RemoveReference() on the iterator's final region */
  static attachedRegions_t::const_iterator attachedBegin(bool threadSafe);
  //! Returns an iterator to the end of the attached regions -- it->first is the key, it->second is the RCRegion*
  /*! If you need thread-safety (i.e. another thread may attach/detach while you are iterating), be sure to use attachedAdvance() to decrement the iterator!
   *  This doesn't prevent other threads from attaching/detaching regions, it only prevents detaching the one you're on. */
  static attachedRegions_t::const_iterator attachedEnd();
  //! Increments the attached region iterator in a thread-safe way -- only use this if you previously passed 'true' to begin(), or are decrementing from end()
  /*! If you are using an iterator obtained without thread-safety, just increment it normally -- don't switch to this or it will screw up reference counting.
   *  If you insist on switching back and forth between thread-safe advance (this function) and normal iterator advancing, you will need to add a reference to the current iterator's region before calling this.
   *  When you're done, either advance off the end, or manually call RemoveReference() on the iterator's final region */
  static void attachedAdvance(attachedRegions_t::const_iterator& it, int x=1);
  
  //! Different methods of handling regions with conflicting keys
  enum ConflictResolutionStrategy {
    RENAME,  //!< try another key until we find one that works (better for SYSV, maybe not so smart for POSIX)
    REPLACE, //!< delete the other region and try again (better for POSIX, maybe not so smart for SYSV)
    EXIT //!< go home and cry about it
  };
  
  static void setConflictResolution(ConflictResolutionStrategy crs) { conflictStrategy=crs; } //!< sets #conflictStrategy
  static ConflictResolutionStrategy getConflictResolution() { return conflictStrategy; } //!< returns #conflictStrategy
  
  static void setMultiprocess(bool mp) { multiprocess=mp; } //!< sets #multiprocess
  static bool getMultiprocess() { return multiprocess; } //!< returns #multiprocess

  
protected:
  //! this protected constructor is used for attaching regions previously created by another process (see attach())
  RCRegion(const Identifier& rid)
    : id(), base(NULL), references(NULL)
  { init(rid.size,rid.key,false); }

  ~RCRegion(); //!< prevents stack allocation -- needs to be heap allocated and reference counted

  //! the alignment multiple of the extra space at the end of the region
  static const unsigned int align=sizeof(unsigned int);
  //! the amount of space to leave at the end of the region for housekeeping (reference counts)
  static const unsigned int extra=sizeof(unsigned int)*(ProcessID::NumProcesses+1);
  //! returns the size of the region to be allocated, given the size requested by the client
  static unsigned int calcRealSize(unsigned int size);

  //! intializes and returns #staticLock
  static Thread::Lock& getStaticLock();

#if TEKKOTSU_SHM_STYLE==SYSV_SHM
  //! initializes the region's information, either creating a new shared memory region or attempting to connect to a pre-existing one
  void init(size_t sz, key_t sug_key, bool create);
#elif TEKKOTSU_SHM_STYLE==POSIX_SHM
  //! returns the qualified version of this region's key (see getQualifiedName(const std::string& key) )
  std::string getQualifiedName() const { return getQualifiedName(id.key); }
  //! wraps the region's key with a root path prefix and optionally a PID suffix (see #useUniqueMemoryRegions and #shmRoot)
  static std::string getQualifiedName(const std::string& key);
  //! opens a region either in "pure" shared memory, or in file-backed shared memory, based on whether USE_UNBACKED_SHM is defined
  int openRegion(int mode) const;
  //! unlinks a region either in "pure" shared memory, or in file-backed shared memory, based on whether USE_UNBACKED_SHM is defined
  bool unlinkRegion() const;
  //! initializes the region's information, either creating a new shared memory region or attempting to connect to a pre-existing one
  void init(size_t sz, const std::string& name, bool create);
#elif TEKKOTSU_SHM_STYLE==NO_SHM
  //! initializes the region's information, either pointing to an existing region or allocating a new one
  void init(size_t sz, const std::string& name, bool create);
#endif

  //! controls what to do about creating a region with a conflicting key (i.e. another region already exists with the same key)
  static ConflictResolutionStrategy conflictStrategy;
  //! set to true if we are shutting down because of an error, and trying to unload shared regions to avoid leaking beyond program scope
  static bool isFaultShutdown;
  //! set to false if the different "processes" are just threads (and thus the last process reference shouldn't actually trigger unlinking a region
  static bool multiprocess;
                    
  static Thread::Lock* staticLock; //!< a lock over all static RCRegion members for the current process, must be obtained before changing reference counts or attaching/detaching regions

  static key_t nextKey; //!< serial number of next key -- starts at 1024 for TEKKOTSU_SHM_STYLE==SYSV_SHM, 0 for POSIX_SHM
  static attachedRegions_t attachedRegions; //!< a mapping of key values to RCRegion pointers of the attached region
  
  Identifier id; //!< key values for the region, namely the system key type (either an integer or string depending on TEKKOTSU_SHM_STYLE) and the size of the region
  char * base; //!< pointer to the region's user data
  unsigned int * references; //!< pointer to the per-process reference counts (stored within the shared region!)

private:
  RCRegion(const RCRegion& r); //!< don't call
  RCRegion& operator=(const RCRegion& r); //!< don't call
};

/*! @file
 * @brief Describes RCRegion, which provides compatability with the OPEN-R type of the same name
 * @author ejt (Creator)
 */

#  endif
#endif