446 lines
11 KiB
C++
446 lines
11 KiB
C++
#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <errno.h>
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#include <memory>
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#include "db.hh"
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#include "util.hh"
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#include "pathlocks.hh"
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/* Wrapper class to ensure proper destruction. */
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class DestroyDbc
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{
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Dbc * dbc;
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public:
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DestroyDbc(Dbc * _dbc) : dbc(_dbc) { }
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~DestroyDbc() { dbc->close(); /* close() frees dbc */ }
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};
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static void rethrow(DbException & e)
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{
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throw Error(e.what());
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}
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Transaction::Transaction()
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: txn(0)
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{
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}
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Transaction::Transaction(Database & db)
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: txn(0)
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{
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begin(db);
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}
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Transaction::~Transaction()
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{
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if (txn) abort();
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}
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void Transaction::begin(Database & db)
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{
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assert(txn == 0);
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db.requireEnv();
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try {
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db.env->txn_begin(0, &txn, 0);
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} catch (DbException e) { rethrow(e); }
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}
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void Transaction::commit()
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{
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if (!txn) throw Error("commit called on null transaction");
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debug(format("committing transaction %1%") % (void *) txn);
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DbTxn * txn2 = txn;
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txn = 0;
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try {
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txn2->commit(0);
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} catch (DbException e) { rethrow(e); }
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}
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void Transaction::abort()
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{
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if (!txn) throw Error("abort called on null transaction");
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debug(format("aborting transaction %1%") % (void *) txn);
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DbTxn * txn2 = txn;
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txn = 0;
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try {
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txn2->abort();
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} catch (DbException e) { rethrow(e); }
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}
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void Transaction::moveTo(Transaction & t)
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{
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if (t.txn) throw Error("target txn already exists");
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t.txn = txn;
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txn = 0;
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}
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void Database::requireEnv()
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{
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checkInterrupt();
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if (!env) throw Error("database environment is not open "
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"(maybe you don't have sufficient permission?)");
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}
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Db * Database::getDb(TableId table)
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{
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if (table == 0)
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throw Error("database table is not open "
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"(maybe you don't have sufficient permission?)");
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map<TableId, Db *>::iterator i = tables.find(table);
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if (i == tables.end())
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throw Error("unknown table id");
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return i->second;
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}
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Database::Database()
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: env(0)
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, nextId(1)
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{
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}
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Database::~Database()
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{
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close();
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}
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int getAccessorCount(int fd)
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{
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if (lseek(fd, 0, SEEK_SET) == -1)
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throw SysError("seeking accessor count");
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char buf[128];
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int len;
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if ((len = read(fd, buf, sizeof(buf) - 1)) == -1)
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throw SysError("reading accessor count");
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buf[len] = 0;
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int count;
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if (sscanf(buf, "%d", &count) != 1) {
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debug(format("accessor count is invalid: `%1%'") % buf);
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return -1;
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}
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return count;
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}
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void setAccessorCount(int fd, int n)
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{
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if (lseek(fd, 0, SEEK_SET) == -1)
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throw SysError("seeking accessor count");
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string s = (format("%1%") % n).str();
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const char * s2 = s.c_str();
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if (write(fd, s2, strlen(s2)) != (ssize_t) strlen(s2) ||
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ftruncate(fd, strlen(s2)) != 0)
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throw SysError("writing accessor count");
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}
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void openEnv(DbEnv * env, const string & path, u_int32_t flags)
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{
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env->open(path.c_str(),
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DB_INIT_LOCK | DB_INIT_LOG | DB_INIT_MPOOL | DB_INIT_TXN |
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DB_CREATE | flags,
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0666);
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}
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static int my_fsync(int fd)
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{
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return 0;
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}
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void Database::open(const string & path)
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{
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if (env) throw Error(format("environment already open"));
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try {
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debug(format("opening database environment"));
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/* Create the database environment object. */
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DbEnv * env = 0; /* !!! close on error */
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env = new DbEnv(0);
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/* Smaller log files. */
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env->set_lg_bsize(32 * 1024); /* default */
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env->set_lg_max(256 * 1024); /* must be > 4 * lg_bsize */
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/* Write the log, but don't sync. This protects transactions
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against application crashes, but if the system crashes,
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some transactions may be undone. An acceptable risk, I
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think. */
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env->set_flags(DB_TXN_WRITE_NOSYNC | DB_LOG_AUTOREMOVE, 1);
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/* Increase the locking limits. If you ever get `Dbc::get:
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Cannot allocate memory' or similar, especially while
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running `nix-store --verify', just increase the following
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number, then run db_recover on the database to remove the
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existing DB environment (since changes only take effect on
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new environments). */
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env->set_lk_max_locks(10000);
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env->set_lk_max_lockers(10000);
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env->set_lk_max_objects(10000);
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env->set_lk_detect(DB_LOCK_DEFAULT);
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/* Dangerous, probably, but from the docs it *seems* that BDB
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shouldn't sync when DB_TXN_WRITE_NOSYNC is used, but it
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still fsync()s sometimes. */
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db_env_set_func_fsync(my_fsync);
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/* The following code provides automatic recovery of the
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database environment. Recovery is necessary when a process
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dies while it has the database open. To detect this,
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processes atomically increment a counter when they open the
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database, and decrement it when they close it. If we see
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that counter is > 0 but no processes are accessing the
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database---determined by attempting to obtain a write lock
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on a lock file on which all accessors have a read lock---we
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must run recovery. Note that this also ensures that we
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only run recovery when there are no other accessors (which
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could cause database corruption). */
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/* !!! close fdAccessors / fdLock on exception */
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/* Open the accessor count file. */
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string accessorsPath = path + "/accessor_count";
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fdAccessors = ::open(accessorsPath.c_str(), O_RDWR | O_CREAT, 0666);
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if (fdAccessors == -1)
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if (errno == EACCES)
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throw DbNoPermission(
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format("permission denied to database in `%1%'") % accessorsPath);
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else
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throw SysError(format("opening file `%1%'") % accessorsPath);
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/* Open the lock file. */
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string lockPath = path + "/access_lock";
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fdLock = ::open(lockPath.c_str(), O_RDWR | O_CREAT, 0666);
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if (fdLock == -1)
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throw SysError(format("opening lock file `%1%'") % lockPath);
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/* Try to acquire a write lock. */
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debug(format("attempting write lock on `%1%'") % lockPath);
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if (lockFile(fdLock, ltWrite, false)) { /* don't wait */
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debug(format("write lock granted"));
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/* We have a write lock, which means that there are no
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other readers or writers. */
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int n = getAccessorCount(fdAccessors);
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if (n != 0) {
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printMsg(lvlTalkative,
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format("accessor count is %1%, running recovery") % n);
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/* Open the environment after running recovery. */
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openEnv(env, path, DB_RECOVER);
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}
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else
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/* Open the environment normally. */
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openEnv(env, path, 0);
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setAccessorCount(fdAccessors, 1);
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/* Downgrade to a read lock. */
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debug(format("downgrading to read lock on `%1%'") % lockPath);
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lockFile(fdLock, ltRead, true);
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} else {
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/* There are other accessors. */
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debug(format("write lock refused"));
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/* Acquire a read lock. */
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debug(format("acquiring read lock on `%1%'") % lockPath);
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lockFile(fdLock, ltRead, true); /* wait indefinitely */
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/* Increment the accessor count. */
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lockFile(fdAccessors, ltWrite, true);
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int n = getAccessorCount(fdAccessors) + 1;
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setAccessorCount(fdAccessors, n);
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debug(format("incremented accessor count to %1%") % n);
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lockFile(fdAccessors, ltNone, true);
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/* Open the environment normally. */
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openEnv(env, path, 0);
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}
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this->env = env;
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} catch (DbException e) { rethrow(e); }
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}
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void Database::close()
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{
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if (!env) return;
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/* Close the database environment. */
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debug(format("closing database environment"));
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try {
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for (map<TableId, Db *>::iterator i = tables.begin();
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i != tables.end(); i++)
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{
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Db * db = i->second;
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db->close(DB_NOSYNC);
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delete db;
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}
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/* Do a checkpoint every 128 kilobytes, or every 5 minutes. */
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env->txn_checkpoint(128, 5, 0);
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env->close(0);
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} catch (DbException e) { rethrow(e); }
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delete env;
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/* Decrement the accessor count. */
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lockFile(fdAccessors, ltWrite, true);
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int n = getAccessorCount(fdAccessors) - 1;
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setAccessorCount(fdAccessors, n);
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debug(format("decremented accessor count to %1%") % n);
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lockFile(fdAccessors, ltNone, true);
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::close(fdAccessors);
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::close(fdLock);
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}
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TableId Database::openTable(const string & tableName)
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{
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requireEnv();
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TableId table = nextId++;
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try {
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Db * db = new Db(env, 0);
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try {
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db->open(0, tableName.c_str(), 0,
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DB_HASH, DB_CREATE | DB_AUTO_COMMIT, 0666);
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} catch (...) {
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delete db;
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throw;
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}
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tables[table] = db;
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} catch (DbException e) { rethrow(e); }
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return table;
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}
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bool Database::queryString(const Transaction & txn, TableId table,
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const string & key, string & data)
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{
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checkInterrupt();
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try {
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Db * db = getDb(table);
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Dbt kt((void *) key.c_str(), key.length());
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Dbt dt;
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int err = db->get(txn.txn, &kt, &dt, 0);
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if (err) return false;
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if (!dt.get_data())
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data = "";
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else
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data = string((char *) dt.get_data(), dt.get_size());
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} catch (DbException e) { rethrow(e); }
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return true;
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}
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bool Database::queryStrings(const Transaction & txn, TableId table,
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const string & key, Strings & data)
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{
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string d;
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if (!queryString(txn, table, key, d))
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return false;
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data = unpackStrings(d);
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return true;
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}
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void Database::setString(const Transaction & txn, TableId table,
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const string & key, const string & data)
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{
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checkInterrupt();
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try {
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Db * db = getDb(table);
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Dbt kt((void *) key.c_str(), key.length());
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Dbt dt((void *) data.c_str(), data.length());
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db->put(txn.txn, &kt, &dt, 0);
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} catch (DbException e) { rethrow(e); }
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}
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void Database::setStrings(const Transaction & txn, TableId table,
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const string & key, const Strings & data, bool deleteEmpty)
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{
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if (deleteEmpty && data.size() == 0)
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delPair(txn, table, key);
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else
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setString(txn, table, key, packStrings(data));
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}
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void Database::delPair(const Transaction & txn, TableId table,
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const string & key)
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{
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checkInterrupt();
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try {
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Db * db = getDb(table);
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Dbt kt((void *) key.c_str(), key.length());
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db->del(txn.txn, &kt, 0);
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/* Non-existence of a pair with the given key is not an
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error. */
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} catch (DbException e) { rethrow(e); }
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}
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void Database::enumTable(const Transaction & txn, TableId table,
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Strings & keys)
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{
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try {
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Db * db = getDb(table);
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Dbc * dbc;
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db->cursor(txn.txn, &dbc, 0);
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DestroyDbc destroyDbc(dbc);
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Dbt kt, dt;
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while (dbc->get(&kt, &dt, DB_NEXT) != DB_NOTFOUND) {
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checkInterrupt();
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keys.push_back(
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string((char *) kt.get_data(), kt.get_size()));
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}
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} catch (DbException e) { rethrow(e); }
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}
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