Changeset 31813 in webkit for trunk/JavaScriptCore/kjs

Timestamp:

Apr 11, 2008, 9:40:15 AM (17 years ago)

Author:

[email protected]

Message:

Reviewed by Geoff.

Make DateMath.cpp thread safe.

No measurable change on SunSpider (should be a very small speedup).

• kjs/DateMath.cpp: (KJS::mimimumYearForDST): (KJS::equivalentYearForDST): Got rid of double caching of the same precomputed value. (KJS::calculateUTCOffset): (KJS::getUTCOffset): Factored actual UTC offset calculation code out of getUTCOffset(), and notification setup into initDateMath().

(KJS::initDateMath): Added.

• kjs/DateMath.h:
• kjs/InitializeThreading.cpp: (KJS::initializeThreading): Added initDateMath().

Location:

trunk/JavaScriptCore/kjs

Files:

• DateMath.cpp (modified) (6 diffs)
• DateMath.h (modified) (1 diff)
• InitializeThreading.cpp (modified) (2 diffs)

trunk/JavaScriptCore/kjs/DateMath.cpp

@@ -318 +318 @@
 }
 
-// It is ok if the cached year is not the current year (e.g. Dec 31st)
-// so long as the rules for DST did not change between the two years, if it does
-// the app would need to be restarted.
-static int mimimumYearForDST()
+static inline int mimimumYearForDST()
 {
     // Because of the 2038 issue (see maximumYearForDST) if the current year is
@@ -327 +324 @@
     // minus 27 instead, to ensure there is a range of 28 years that all years
     // can map to.
-    static int minYear = std::min(msToYear(getCurrentUTCTime()), maximumYearForDST() - 27) ;
-    return minYear;
+    return std::min(msToYear(getCurrentUTCTime()), maximumYearForDST() - 27) ;
 }
 
@@ -343 +339 @@
 int equivalentYearForDST(int year)
 {
+    // It is ok if the cached year is not the current year as long as the rules
+    // for DST did not change between the two years; if they did the app would need
+    // to be restarted.
     static int minYear = mimimumYearForDST();
-    static int maxYear = maximumYearForDST();
+    int maxYear = maximumYearForDST();
 
     int difference;
@@ -362 +361 @@
 }
 
+static int32_t calculateUTCOffset()
+{
+    tm localt;
+    memset(&localt, 0, sizeof(localt));
+ 
+    // get the difference between this time zone and UTC on Jan 01, 2000 12:00:00 AM
+    localt.tm_mday = 1;
+    localt.tm_year = 100;
+    time_t utcOffset = 946684800 - mktime(&localt);
+
+    return static_cast<int32_t>(utcOffset * 1000);
+}
+
+#if PLATFORM(DARWIN)
+static int32_t s_cachedUTCOffset; // In milliseconds. An assumption here is that access to an int32_t variable is atomic on platforms that take this code path.
+static bool s_haveCachedUTCOffset;
+static int s_notificationToken;
+#endif
+
 /*
  * Get the difference in milliseconds between this time zone and UTC (GMT)
@@ -369 +387 @@
 {
 #if PLATFORM(DARWIN)
-    // Register for a notification whenever the time zone changes.
-    static bool triedToRegister = false;
-    static bool haveNotificationToken = false;
-    static int notificationToken;
-    if (!triedToRegister) {
-        triedToRegister = true;
-        uint32_t status = notify_register_check("com.apple.system.timezone", &notificationToken);
-        if (status == NOTIFY_STATUS_OK)
-            haveNotificationToken = true;
+    if (s_haveCachedUTCOffset) {
+        int notified;
+        uint32_t status = notify_check(s_notificationToken, &notified);
+        if (status == NOTIFY_STATUS_OK && !notified)
+            return s_cachedUTCOffset;
     }
-
-    // If we can verify that we have not received a time zone notification,
-    // then use the cached offset from the last time this function was called.
-    static bool haveCachedOffset = false;
-    static double cachedOffset;
-    if (haveNotificationToken && haveCachedOffset) {
-        int notified;
-        uint32_t status = notify_check(notificationToken, &notified);
-        if (status == NOTIFY_STATUS_OK && !notified)
-            return cachedOffset;
-    }
-#endif
-
-    tm localt;
-
-    memset(&localt, 0, sizeof(localt));
-
-    // get the difference between this time zone and UTC on Jan 01, 2000 12:00:00 AM
-    localt.tm_mday = 1;
-    localt.tm_year = 100;
-    double utcOffset = 946684800.0 - mktime(&localt);
-
-    utcOffset *= msPerSecond;
+#endif
+
+    int32_t utcOffset = calculateUTCOffset();
 
 #if PLATFORM(DARWIN)
-    haveCachedOffset = true;
-    cachedOffset = utcOffset;
+    // Theoretically, it is possible that several threads will be executing this code at once, in which case we will have a race condition,
+    // and a newer value may be overwritten. In practice, time zones don't change that often.
+    s_cachedUTCOffset = utcOffset;
 #endif
 
@@ -507 +502 @@
 }
 
+void initDateMath()
+{
+#ifndef NDEBUG
+    static bool alreadyInitialized;
+    ASSERT(!alreadyInitialized++);
+#endif
+
+    equivalentYearForDST(2000); // Need to call once to initialize a static used in this function.
+#if PLATFORM(DARWIN)
+    // Register for a notification whenever the time zone changes.
+    uint32_t status = notify_register_check("com.apple.system.timezone", &s_notificationToken);
+    if (status == NOTIFY_STATUS_OK) {
+        s_cachedUTCOffset = calculateUTCOffset();
+        s_haveCachedUTCOffset = true;
+    }
+#endif
+}
+
 } // namespace KJS

trunk/JavaScriptCore/kjs/DateMath.h

@@ -50 +50 @@
 struct GregorianDateTime;
 
+void initDateMath();
 void msToGregorianDateTime(double, bool outputIsUTC, GregorianDateTime&);
 double gregorianDateTimeToMS(const GregorianDateTime&, double, bool inputIsUTC);

trunk/JavaScriptCore/kjs/InitializeThreading.cpp

@@ -30 +30 @@
 #include "InitializeThreading.h"
 
+#include "DateMath.h"
 #include "dtoa.h"
 #include "ustring.h"
@@ -40 +41 @@
     WTF::initializeThreading();
 #if USE(MULTIPLE_THREADS)
-    if (!s_dtoaP5Mutex)
+    if (!s_dtoaP5Mutex) {
         s_dtoaP5Mutex = new Mutex;
-    UString::null();
+        UString::null();
+        initDateMath();
+    }
 #endif
 }